Actoplus Met (pioglitazone HCl/metformin HCl)

Available as metformin hydrochloride; dosage expressed in terms of the salt.

Dosage of pioglitazone hydrochloride is expressed in terms of pioglitazone.

Metformin hydrochloride is administered orally. In patients receiving metformin hydrochloride immediate-release tablets at a dosage of 2 g or less daily, the medication can usually be given as 2 divided doses daily; however, in patients who require more than 2 g daily, the medication may be better tolerated if administered in 3 divided doses daily. Although food decreases the extent and slightly delays absorption of metformin immediate-release tablets, the manufacturer recommends that the medication be taken with meals to decrease adverse GI effects. Immediate-release metformin hydrochloride in fixed combination with alogliptin, canagliflozin, dapagliflozin, empagliflozin, ertugliflozin, linagliptin, pioglitazone, or sitagliptin is administered in divided doses daily with meals to reduce the GI effects of the metformin hydrochloride component. See the full prescribing information for additional administration instructions for the combination products.

Metformin hydrochloride oral solution is administered either once or twice daily with meals. Dosages above 2 g daily may be better tolerated if administered in 3 divided doses daily. Each dose should be measured using a metformin hydrochloride oral solution specific dosing cup.

Metformin hydrochloride extended-release tablets usually are taken with the evening meal. Extended-release metformin hydrochloride in fixed combination with canagliflozin, dapagliflozin, or empagliflozin is administered once daily with the morning meal. The fixed combination of extended-release metformin hydrochloride and linagliptin should be administered once daily with a meal. The fixed combination of extended-release metformin hydrochloride and sitagliptin should be administered once daily with a meal, preferably with the evening meal. Extended-release metformin hydrochloride in fixed combination with saxagliptin should be administered once daily with the evening meal. Extended-release metformin hydrochloride tablets and fixed-combination preparations containing the extended-release form of the medication must be swallowed whole and not chewed, cut, or crushed; inactive ingredients occasionally may be eliminated in feces as a soft mass that may resemble the original tablet. See the full prescribing information for additional administration instructions for the combination products.

Store metformin hydrochloride immediate- and extended-release tablets at 20--25degreesC in light-resistant containers; excursions permitted to 15--30degreesC. Store metformin hydrochloride oral solution at 15--30degreesC.

Pioglitazone hydrochloride is administered orally once daily and can be taken without regard to meals. The fixed combination of pioglitazone and immediate-release metformin hydrochloride should be administered orally with meals to reduce the GI effects of the metformin component. The fixed combination of pioglitazone and glimepiride is administered once daily with the first main meal. See full prescribing for additional administration instructions for these fixed-combination products.

If a dose of pioglitazone is missed on one day, the dose should not be doubled the following day.

Store pioglitazone tablets at 25oC; excursions permitted to 15--30oC. Keep container closed and protect from light, moisture, and humidity.

Pioglitazone is metabolized principally by cytochrome P-450 (CYP) 2C8, and to a lesser degree, by CYP3A4, with additional contributions from a variety of isoforms including the mainly extrahepatic CYP1A1.

Pioglitazone is a weak inducer of CYP3A4.

Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

Cyp3a4 Inducers/Lumateperone

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Lumateperone is a substrate of CYP3A4. Inducers of CYP3A4 may induce the metabolism of lumateperone.(1)

CLINICAL EFFECTS: The concurrent administration of a CYP3A4 inducer may decrease the exposure to lumateperone.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: The manufacturer of lumateperone states that concurrent use with CYP3A4 inducers should be avoided.(1)

DISCUSSION: Coadministration of lumateperone with rifampin, a strong CYP3A4 inducer, resulted in a 98% reduction in area-under-curve (AUC) and a 90% reduction in concentration maximum (Cmax).(1) Strong inducers of CYP3A4 include: apalutamide, barbiturates, carbamazepine, encorafenib, enzalutamide, fosphenytoin, ivosidenib, lumacaftor, mitotane, phenobarbital, phenytoin, primidone, rifampin, rifapentine, and St. John's wort.(2,3) Moderate inducers of CYP3A4 include: belzutifan, bosentan, cenobamate, dabrafenib, efavirenz, elagolix, etravirine, fexinidazole, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, repotrectinib, rifabutin, telotristat, thioridazine, and tovorafenib.(2,3) Weak inducers of CYP3A4 include: amprenavir, armodafinil, aumolertinib, bexarotene, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, eslicarbazepine, garlic, genistein, gingko, ginseng, glycyrrhizin, nevirapine, omaveloxolone, oxcarbazepine, pioglitazone, quercetin, rufinamide, sotorasib, sulfinpyrazone, sunvozertinib, tecovirimat, terbinafine, ticlopidine, troglitazone, vemurafenib, and vinblastine.(2,3)

Cyp3a4 Inducers/Zuranolone

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Inducers of CYP3A4 may induce the metabolism of zuranolone.(1)

CLINICAL EFFECTS: Concurrent use of a CYP3A4 inducer may result in a loss of zuranolone efficacy.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: Avoid the concurrent use of zuranolone with CYP3A4 inducers.(1)

DISCUSSION: Coadministration of zuranolone with rifampin decreased the maximum concentration (Cmax) by 0.31-fold and area-under-curve (AUC) by 0.15-fold.(1) Strong CYP3A4 inducers linked to this monograph include: apalutamide, barbiturates, carbamazepine, encorafenib, enzalutamide, fosphenytoin, ivosidenib, lumacaftor, mitotane, phenobarbital, phenytoin, primidone, rifampin, rifapentine, and St. John's wort. Moderate CYP3A4 inducers linked to this monograph include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, fexinidazole, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, rifabutin, sotorasib, telotristat ethyl, thioridazine, and tovorafenib. Weak CYP3A4 inducers linked to this monograph include: armodafinil, aumolertinib, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, eslicarbazepine, flucloxacillin, garlic, genistein, ginseng, glycyrrhizin, methylprednisolone, mobocertinib, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(2,3)

Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

Antidiabetic Agents/Gatifloxacin

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: The exact mechanism is unknown.

CLINICAL EFFECTS: Concurrent use of gatifloxacin may result in hypoglycemia and/or hyperglycemia.(1-4) Hypoglycemia is more common during the first three days of concurrent therapy. Hyperglycemia is more common after the first three days of concurrent therapy.(2)

PREDISPOSING FACTORS: Elderly patients, especially those with decreased renal function may be predisposed to this interaction.(2)

PATIENT MANAGEMENT: Patients receiving concurrent gatifloxacin should be closely monitored for hypoglycemia during the first three days of concurrent therapy and for hyperglycemia after the first three days of concurrent therapy. Patients should be instructed to discontinue gatifloxacin if hypoglycemia or hyperglycemia occur.(2)

DISCUSSION: Hypoglycemia has been reported with gatifloxacin and glyburide(1,5,6) or glimepiride.(7) In a study in patients with type 2 diabetes mellitus, concurrent gatifloxacin (400 mg daily for 10 days) had no effect on the pharmacokinetics of glyburide (steady state daily regimen); however, pharmacodynamic interactions have been reported.(2) Health Canada has received 19 reports of hypoglycemia in patients taking gatifloxacin. Seventeen of these involved concurrent hypoglycemic agents. Health Canada has received 2 reports of hyperglycemia in patients taking gatifloxacin and hypoglycemic agents. Health Canada has received 2 reports of patients experiencing hypoglycemia and hyperglycemia during concurrent gatifloxacin and hypoglycemic agents.(3) In a study, 13 reports of dysglycemia were reported in patients taking gatifloxacin. Ten of these patients had diabetes mellitus and were on concurrent hypoglycemic agents. Of these ten patients, nine patients experienced hypoglycemia, while one patient experienced hyperglycemia.(8)

Cyp3a4 Inducers/Erlotinib

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Inducers of CYP3A4 may induce the metabolism of erlotinib.(1)

CLINICAL EFFECTS: Concurrent or recent use of a CYP3A4 inducer may result in decreased levels and effectiveness of erlotinib.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: Avoid the concurrent use of CYP3A4 inducers in patients receiving therapy with erlotinib. Consider the use of alternative agents with less enzyme induction potential.(1) Consider increasing the dosage of erlotinib by 50 mg increments as tolerated at two week intervals (to a maximum of 450 mg) while closely monitoring the patient. The highest dosage studied with concurrent rifampin is 450 mg. If the dosage of erlotinib is increased, it will need to be decreased when the inducer is discontinued.(1)

DISCUSSION: Pretreatment and concurrent therapy with rifampin increased erlotinib clearance by 3-fold and decreased the erlotinib area-under-curve (AUC) by 66% to 80%. This is equivalent to a dose of about 30 mg to 50 mg in NSCLC.(1) In a study, pretreatment with rifampin for 11 days decreased the AUC of a single 450 mg dose of erlotinib to 57.6% of the AUC observed with a single 150 mg dose of erlotinib.(1) In a case report, coadministration of phenytoin (180mg daily) and erlotinib (150mg daily) increased the phenytoin concentration from 8.2mcg/ml to 24.2mcg/ml and decreased the erlotinib concentration 12-fold (from 1.77mcg/ml to 0.15mcg/ml) and increased the erlotinib clearance by 10-fold (from 3.53 L/h to 41.7 L/h).(2) In a study, concurrent use of sorafenib (400 mg twice daily) and erlotinib (150 mg daily) decreased the concentration minimum (Cmin), concentration maximum (Cmax), and AUC of erlotinib.(3) In an animal study, concurrent use of dexamethasone and erlotinib decreased the AUC of erlotinib by 0.6-fold.(4) Strong inducers of CYP3A4 include: barbiturates, encorafenib, enzalutamide, fosphenytoin, ivosidenib, mitotane, phenobarbital, phenytoin, primidone, rifampin, and rifapentine.(5,6) Moderate inducers of CYP3A4 include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, fexinidazole, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, sotorasib, telotristat, thioridazine, and tovorafenib.(5,6) Weak inducers of CYP3A4 include: amprenavir, armodafinil, aumolertinib, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dicloxacillin, echinacea, eslicarbazepine, flucloxacillin, garlic, genistein, ginkgo, ginseng, glycyrrhizin, mobocertinib, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(5,6)

Metformin/Iodinated Contrast Materials

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Use of iodinated contrast materials may result in acute changes in renal function, resulting in a decrease in metformin clearance.(1-3)

CLINICAL EFFECTS: Use of iodinated contrast materials may increase levels of metformin, which may result in lactic acidosis.(1-3)

PREDISPOSING FACTORS: Pre-existing renal dysfunction may contribute to decreased clearance of metformin. Other factors which may increase the risk for lactic acidosis include age greater than 65 years, dehydration, metabolic acidosis, sepsis, a history of hepatic impairment, alcoholism, or heart failure.(1-4)

PATIENT MANAGEMENT: Evaluate renal function prior to contrast procedure. According to manufacturer recommendations, discontinue metformin at the time of, or prior to, the contrast imaging procedure in patients with a history of liver disease, alcoholism, heart failure, or if contrast is to be administered intra-arterially. When contrast is to be administered by other routes, discontinue metformin at the time of, or prior to, the procedure for patients with an estimated glomerular filtration rate (eGFR) of 30 to 60 mL/min/1.73 m2. Re-evaluate eGFR 48 hours after the imaging procedure and restart metformin if renal function is stable. Discontinuation of metformin is not required if eGFR is > 60 mL/min/1.73 m2.(4) According to American College of Radiology guidelines, discontinue metformin at the time of, or prior to, the contrast imaging procedure in patients with acute kidney injury or chronic kidney disease (Stage IV or V or eGFR < 30 mL/min/1.73 m2), or who are undergoing arterial catheter studies that might result in emboli (atheromatous or other) to the renal arteries. Re-evaluate eGFR 48 hours after the imaging procedure and restart metformin if renal function is normal. Discontinuation of metformin is not required in patients with no evidence of acute kidney injury and with eGFR >= 30 mL/min/m2.(5)

DISCUSSION: An FDA review of the medical literature showed that metformin may be safely used in patients with mild or moderate renal impairment, resulting in modifications of prescribing recommendations and method for evaluation of renal function.(4) A clinical review of 33 patients on metformin who had received contrast media showed elevations in serum creatinine of the four patients with baseline elevations. The 29 patients with normal baseline renal function showed no elevations after administration of contrast media. The authors recommend that a baseline serum creatinine is obtained for all patients and that metformin should only be discontinued in patients with baseline elevations.(6) A retrospective study of ninety-seven patients currently taking metformin underwent a radiologic procedure with contrast media. Of these patients, 4 developed contrast material associated nephropathy and eight patients had an increased risk of lactic acidosis, with a baseline serum creatinine <1.5mg/dl.(7) A prospective clinical trial with 50 diabetic patients on metformin with baseline serum creatinine <1.47mg/dl showed no statistical difference in renal function before and 48 hours after administration of contrast media. The authors recommend a baseline serum creatinine for all patients and suggest that temporary discontinuation of metformin may not be necessary when baseline renal function is <1.47mg/dl.(8) A systematic review of the literature reveals that 17 of 18 case reports of metformin-induced lactic acidosis involved patients with renal dysfunction prior to administration of contrast media. The authors recommend a baseline serum creatinine in all patients and if renal dysfunction is present, metformin should be discontinued for 48 hours before and after administration of contrast media. The authors recommend follow-up creatinine measurement in patients with prior renal impairment or known comorbidities affecting lactate levels.(9)

Metformin/Tafenoquine

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Metformin renal clearance is mediated by OCT2 and MATE1 transporters.(1) Tafenoquine inhibits elimination by these pathways.(2)

CLINICAL EFFECTS: Use of tafenoquine may increase levels of metformin, which may result in lactic acidosis.

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment, sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population.

PATIENT MANAGEMENT: The US labeling for metformin recommends the dose of metformin be adjusted as needed.(1) The manufacturer of tafenoquine states the concurrent administration of tafenoquine with OCT2 and MATE1 substrates, such as metformin, should be avoided. If coadministration cannot be avoided, monitor for drug-related toxicities.(2) Evaluate patient's renal function and consider discontinuation in patients with renal impairment. Monitor for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, respiratory distress, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: elevated blood lactate levels (greater than 5 mmol/L), low pH, an increased anion gap, and increased lactate to pyruvate ratio.

DISCUSSION: Metformin renal clearance is mediated by OCT2 and MATE1 transporters.(1) Tafenoquine is believed to inhibit the OCT2 and MATE1 pathways.(2)

Pioglitazone (<=15Mg); Rosiglitazone/Strong Cyp2c8 Inhibitor

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Strong CYP2C8 inhibitors may inhibit the metabolism of pioglitazone(1-5) and rosiglitazone.(6)

CLINICAL EFFECTS: Concurrent use of strong CYP2C8 inhibitors may result in elevated levels of and clinical effects, including severe hypoglycemia, from pioglitazone(1-5) or rosiglitazone.(6,7)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Consider avoiding strong inhibitors of CYP2C8 in patients maintained on pioglitazone or rosiglitazone. The maximum recommended dosage of pioglitazone is 15 mg daily when used concurrently with gemfibrozil or other strong CYP2C8 inhibitors.(2) The dosage of pioglitazone(2) or rosiglitazone(7) may need to be adjusted if gemfibrozil is initiated or discontinued. If concurrent therapy is warranted, patients should be closely monitored for increased response to pioglitazone or rosiglitazone.

DISCUSSION: In a randomized, cross-over study in 10 healthy subjects, pretreatment with gemfibrozil (600 mg daily for 3 days) increased the the area-under-curve (AUC) of a single dose of pioglitazone (30 mg) by 3.4-fold. The AUC of the ratios of the M-III metabolite/pioglitazone and M-IV metabolite/pioglitazone were reduced by 71% and by 65%, respectively. (1,2) In a randomized, double-blind, cross-over study in 12 healthy subjects, pretreatment with gemfibrozil (600 mg daily for 3 days) increased the AUC and half-life (T1/2) of a single dose of pioglitazone (15 mg) by 3.2-fold (range 2.3-fold to 6.5-fold) and by 1.7-fold, respectively. There was no significant effect on pioglitazone maximum concentration (Cmax). The 0-48 hour AUC of the M-III and M-IV metabolites were decreased by 42% and by 45%, respectively; however, there was no significant effect on their 0-infinity AUC.(3) In a randomized, cross-over study, gemfibrozil (600 mg twice daily for 4 days) increased the AUC of a single dose of pioglitazone (15 mg) by 4.3-fold. The increase was variable between CYP2C8 genotypes. Individuals who were CYP2C8*3 carriers had a 5.2-fold increase in pioglitazone, while CYP2C8*1 homozygotes had a 3.3-fold increase in pioglitazone.(5) In a randomized crossover study in 10 subjects, gemfibrozil (600 mg twice daily) increased the rosiglitazone (4 mg single dose) AUC by 2.3-fold and increased rosiglitazone T1/2 from 3.6 hours to 7.6 hours. Rosiglitazone Cmax increased 1.2-fold. At 24 hours post dose, the rosiglitazone concentration was 9.8-fold greater when it was taken with gemfibrozil. Gemfibrozil increased the time to Cmax (Tmax) of N-desmethylrosiglitazone from 7 hours to 12 hours and decreased its AUC by 38%.(6) Concurrent use of gemfibrozil (600 mg twice daily) with rosiglitazone (4 mg daily) increased rosiglitazone AUC by 127%.(7) Strong inhibitors of CYP2C8 include: gemfibrozil.(8,9)

Pioglitazone; Repaglinide/Abiraterone

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: The mechanism of interaction is not fully understood but may at least partially involve CYP2C8 inhibition by abiraterone, resulting in decreased metabolism of pioglitazone and repaglinide.(1,2)

CLINICAL EFFECTS: Concurrent use of pioglitazone or repaglinide with abiraterone may result in elevated levels and clinical effects of the anti-diabetic agents, including severe hypoglycemia.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Monitor blood glucose in patients with diabetes during and after discontinuation of treatment with abiraterone. Consider dosage adjustment of pioglitazone or repaglinide to minimize the risk of hypoglycemia.(1)

DISCUSSION: Severe hypoglycemia has been reported in diabetic patients receiving pioglitazone or repaglinide concurrently with abiraterone. A review of the FDA Adverse Events Reporting database found 2 reports of hypoglycemia in patients receiving concurrent abiraterone and repaglinide. One patient was hospitalized with life-threatening outcomes, and the other died, though he also had sepsis and cardiac failure. In a study of 16 healthy volunteers, single-dose abiraterone 1,000 mg increased the maximum concentration (Cmax) and area-under-curve (AUC) of single-dose pioglitazone 15 mg by 23% and 46%.(3)

Moderate Interaction: Assess the risk to the patient and take action as needed.

Antidiabetic Agents/Gymnema

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Gymnema has been shown to increase the number of insulin-secreting beta cells in animals. It has also been shown to increase the activity of enzymes responsible for glucose uptake and utilization and inhibit peripheral utilization of glucose.(1)

CLINICAL EFFECTS: Use of gymnema may result in decreased requirements of antidiabetic agents.(2-4)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Diabetic patients should be carefully monitored if gymnema is initiated or discontinued from concurrent therapy. The dosage of the patient's antidiabetic agent(s) may need to be adjusted.(2)

DISCUSSION: In a study in 22 non-insulin-dependent patients, patients had decreased blood glucose, glycosylated hemoglobin, and glycosylated plasma proteins during gymnema therapy. Patients were able to decrease the dosage of their conventional antidiabetic therapy and five patients were able to discontinue their conventional antidiabetic therapy.(3) In a study in 27 insulin-dependent patients, patients had decreased insulin requirements, fasting blood glucose, glycosylated hemoglobin, and glycosylated plasma protein levels.(4)

Metformin/Bictegravir

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Metformin renal clearance is mediated by OCT2 and MATE1 transport. Bictegravir inhibits elimination by these pathways.(1,2)

CLINICAL EFFECTS: Use of bictegravir may increase levels of metformin, which may result in lactic acidosis.

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment,sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population.

PATIENT MANAGEMENT: The US labeling for metformin recommends the dose of metformin be adjusted as needed.(1) Evaluate patient's renal function and consider discontinuation of one or both agents in patients with renal impairment. Monitor for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: elevated blood lactate levels (greater than 5 mmol/L), low pH, an increased anion gap, and increased lactate to pyruvate ratio.

DISCUSSION: Bictegravir is an inhibitor of OCT2 and MATE1.(2) Trimethoprim, an inhibitor of OCT2 and MATE1, was found to cause significant inhibition of net transcellular chloroquine transport in canine kidney-OCT2-MATE1 cells. Chloroquine is eliminated by renal tubular secretion involving multidrug and toxin extrusion protein 1 (MATE1). Trimethoprim caused concentration-dependent inhibition of net metformin intake in HEK293-MATE1 cells (human embryonic kidney).(3) A randomized, open-label, two-phase crossover study found that trimethoprim inhibited OCT2, MATE1, and MATE2-K-dependent transport of metformin. Trimethoprim increased metformin area-under-curve (AUC) by 29.4% and decreased metformin renal clearance by 26.4%.(4) In a study in 24 healthy volunteers received metformin 500 mg three times daily for ten days and trimethoprim 200 mg twice daily from days 5-10. Trimethoprim significantly reduced the apparent systemic metformin clearance (CL/F) from 74 to 54 l/h and renal metformin clearance from 31 to 21 l/h. Metformin half-life was prolonged from 2.7 to 3.6h. The metformin plasma concentration (Cmax) increased 38% and the AUC by 37%. Trimethoprim was also associated with a decrease in creatinine clearance and an increase in plasma lactate. (5)

Metformin/Carbonic Anhydrase Inhibitors

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Carbonic anhydrase inhibitors increase bicarbonate excretion which may cause metabolic acidosis.(1) High systemic concentrations of metformin may result in lactic acidosis.(2,3) Topiramate, a mild carbonic anhydrase inhibitor, may also increase systemic exposure to metformin.(1)

CLINICAL EFFECTS: Carbonic anhydrase inhibitors may increase the risk for metformin associated lactic acidosis.(1-3) Untreated lactic acidosis may be fatal. Symptoms of lactic acidosis include malaise, myalgias, respiratory distress, low blood pH, increased anion gap and elevated blood lactate.(2) Carbonic anhydrase inhibitors linked to this monograph are acetazolamide, dichlorphenamide, methazolamide, sulthiame, topiramate, and zonisamide.

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment,sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population. The risk for metabolic acidosis is higher with increased doses of either agent.

PATIENT MANAGEMENT: For patients receiving concurrent therapy, monitor renal function and assure that patient does not have risk factors for metformin associated lactic acidosis. Discontinue metformin when risk factors are present. If both drugs are given, monitor renal function and for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, respiratory distress, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: low pH, an increased anion gap, and increased lactate to pyruvate ratio. Manufacturer recommendations: the manufacturer of metformin recommends caution with concomitant use of carbonic anhydrase inhibitors due to an increased risk for metformin associated lactic acidosis.(2) The manufacturer of topiramate notes that topiramate can frequently cause metabolic acidosis and that metformin should not be used in patients with metabolic acidosis.(1)

DISCUSSION: A literature search for lactic acidosis due solely to the combination of metformin and carbonic anhydrase inhibitors or topiramate did not reveal any case reports of symptomatic metabolic acidosis due to this combination. Never-the-less, since carbonic anhydrase inhibitors act by inhibiting the reabsorption of bicarbonate in the renal tubule, some lowering of systemic bicarbonate and pH is common and supports the plausibility of this interaction. In addition, a pharmacokinetic interaction has been described with topiramate. A study in healthy volunteers evaluated the effect of topiramate 100 mg every 12 hours on the kinetics of metformin 500 mg every 12 hours. Mean metformin exposure (area-under-curve or AUC) was increased 25%.(1)

Metformin/Cephalexin

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Cephalexin may inhibit the renal tubular secretion of metformin.(1,2)

CLINICAL EFFECTS: Concurrent use of cephalexin may result in increased levels and clinical effects of metformin,(1,2) as well as an increased risk of lactic acidosis.

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment, sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population.

PATIENT MANAGEMENT: Patients maintained on metformin should be closely monitored when cephalexin is initiated and discontinued. The dosage of metformin may need to be adjusted.(1)

DISCUSSION: In a randomized, cross-over study in 12 healthy subjects, concurrent metformin (500 mg) and cephalexin (500 mg) increased the maximum concentration (Cmax) and area-under-curve (AUC) of metformin by 34% and 24%, respectively. Metformin renal clearance decreased by 14%.(1,2)

Metformin/Dolutegravir

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Dolutegravir may inhibit the renal organic cation transporter, OCT2, responsible for the elimination of metformin.(1)

CLINICAL EFFECTS: Concurrent use may result in increased plasma levels of metformin and toxicity such as lactic acidosis. Untreated lactic acidosis may be fatal. Symptoms of lactic acidosis include malaise, myalgias, respiratory distress, low pH, increased anion gap and elevated blood lactate.

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment,sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population.

PATIENT MANAGEMENT: With concomitant use, assess the benefit and risk of metformin in patients on dolutegravir. When starting or stopping dolutegravir, the metformin dose may require an adjustment. Monitor blood glucose when initiating concomitant use and after stopping dolutegravir.(1) Monitor patient's renal function and for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, respiratory distress, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: low pH, an increased anion gap, and increased lactate to pyruvate ratio.(1)

DISCUSSION: Dolutegravir has been shown to inhibit OCT2 in vitro and in vivo and is expected to inhibit the excretion of metformin.(1) In a study in 15 subjects, concomitant metformin (500 mg twice daily) with dolutegravir (50 mg daily) increased the concentration maximum (Cmax) and area-under-curve (AUC) of metformin by 66% and 79%, respectively. In a study in 15 subjects, concomitant metformin (500 mg twice daily) with dolutegravir (50 mg twice daily) increased the Cmax and AUC of metformin by 111% and 145%, respectively.(1)

Metformin/Mate Inhibitors

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Inhibitors of the Multidrug and Toxin Extrusion (MATE) protein transporters in the kidneys may interfere with the renal tubular secretion of metformin.(1)

CLINICAL EFFECTS: Concurrent use may result in increased plasma levels of metformin and toxicity such as lactic acidosis. Untreated lactic acidosis may be fatal. Symptoms of lactic acidosis include malaise, myalgias, respiratory distress, low pH, increased anion gap and elevated blood lactate.

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment,sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population. The risk for metabolic acidosis is higher with increased doses of either agent.

PATIENT MANAGEMENT: Use an alternative agent if possible. If both drugs are given, monitor patient's renal function and for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, respiratory distress, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: low pH, an increased anion gap, and increased lactate to pyruvate ratio. Dosage of either agent may need to be adjusted.(1)

DISCUSSION: In a study of normal healthy volunteers, concurrent metformin and oral cimetidine increased metformin maximum concentration (Cmax) in plasma and whole blood by 60% and increased metformin area-under-curve (AUC) levels in plasma and whole blood by 40%.(1) In a study in 7 subjects, concurrent metformin (250 mg daily) with cimetidine (400 mg twice daily) increased metformin AUC by 50%. Metformin renal clearance over 24 hours was reduced by 27%.(2) MATE inhibitors include: brepocitinib, cimetidine, pyrimethamine, and risdiplam.(3)

Metformin/Oct2 Inhibitors

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Agents that inhibit the organic cation transporter 2 (OCT2) may inhibit the excretion of metformin by OCT2 in the kidneys.(1)

CLINICAL EFFECTS: Concurrent use of OCT2 renal transport inhibitors may result in increased levels of and toxicity from metformin.(1)

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment, sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels higher than 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population.

PATIENT MANAGEMENT: Consider the potential benefits against the risks of concurrent use of metformin with OCT2 renal transport inhibitors. If concurrent use is appropriate, monitor for toxicities of metformin and consider dosage reduction of metformin.(1)

DISCUSSION: In a study, givinostat increased the levels of creatinine (OCT2 substrate) by 4.76 umol/L from baseline.(1) OCT2 inhibitors linked to this monograph include: arimoclomol, givinostat, trilaciclib, and vimseltinib.(2)

Metformin/Patiromer

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Patiromer may bind to metformin.(1)

CLINICAL EFFECTS: Concurrent use may result in decreased gastrointestinal absorption and loss of efficacy of metformin.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturer of patiromer recommends that you administer patiromer at least 3 hours before or 3 hours after metformin.(1)

DISCUSSION: A study in healthy volunteers showed that patiromer decreased the systemic exposure of coadministered metformin. No interaction was seen when these drugs were taken 3 hours apart.(1)

Metformin/Ranolazine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Ranolazine may decrease renal elimination of metformin by inhibiting OCT-2.(1)

CLINICAL EFFECTS: Concurrent ranolazine may result in elevated levels of and toxicity from metformin.(1)

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment, sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population.

PATIENT MANAGEMENT: Monitor patients receiving concurrent therapy with metformin and ranolazine. In patients receiving 1000 mg ranolazine twice daily, limit the dose of metformin to 1700 mg daily.(1)

DISCUSSION: In healthy subjects, ranolazine (1000 mg twice daily) increased exposure of metformin by 80%. Ranolazine (500 mg BID) increased metformin exposure by 40%.(1)

Metformin/Trimethoprim

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Metformin renal clearance is mediated by OCT2 and MATE1 transport. Trimethoprim inhibits elimination by these pathways.

CLINICAL EFFECTS: Use of trimethoprim may increase levels of metformin, which may result in lactic acidosis.

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment,sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population.

PATIENT MANAGEMENT: The US labeling for metformin recommends the dose of metformin and/or trimethoprim be adjusted as needed. Consider the benefits and risks of concomitant use.(1) Evaluate patient's renal function and consider discontinuation of one or both agents in patients with renal impairment. Monitor for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, respiratory distress, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: elevated blood lactate levels (greater than 5 mmol/L), low pH, an increased anion gap, and increased lactate to pyruvate ratio.

DISCUSSION: Trimethoprim was found to cause significant inhibition of net transcellular chloroquine transport in canine kidney-OCT2-MATE1 cells. Chloroquine is eliminated by renal tubular secretion involving multidrug and toxin extrusion protein 1 (MATE1). Trimethoprim caused concentration-dependent inhibition of net metformin intake in HEK293-MATE1 cells (human embryonic kidney). (2) A randomized, open-label, two-phase crossover study found that trimethoprim inhibited OCT2, MATE1, and MATE2-K-dependent transport of metformin. Trimethoprim increased metformin area under the curve (AUC) by 29.4% and decreased metformin renal clearance by 26.4%. (3) 24 healthy volunteers received metformin 500 mg three times daily for ten days and trimethoprim 200 mg twice daily from days 5-10. Trimethoprim significantly reduced the apparent systemic metformin clearance (CL/F) from 74 to 54 l/h and renal metformin clearance from 31 to 21 l/h. Metformin half-life was prolonged from 2.7 to 3.6h. The metformin plasma concentration (Cmax) increased 38% and the AUC by 37%. Trimethoprim was also associated with a decrease in creatinine clearance and an increase in plasma lactate. (4)

Metformin/Vandetanib

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Renal tubular secretion of metformin is mediated by organic cation transporter 2 (OCT2) and the multidrug and toxin extrusion protein (MATE) transporter. Vandetanib inhibits elimination by the OCT2 and MATE pathways.(1)

CLINICAL EFFECTS: Use of vandetanib may increase levels of metformin. Concurrent use may result in increased plasma levels of metformin and toxicity such as lactic acidosis. Untreated lactic acidosis may be fatal. Symptoms of lactic acidosis include malaise, myalgias, respiratory distress, low pH, increased anion gap and elevated blood lactate.(1)

PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment, sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population. The risk for metabolic acidosis is higher with increased doses of either agent.

PATIENT MANAGEMENT: Use an alternative agent if possible. The US labeling for vandetanib recommends caution with concomitant use of metformin and close monitoring for metformin toxicity.(1) Evaluate patient's renal function and consider discontinuation of one or both agents in patients with renal impairment. Monitor for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, respiratory distress, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: elevated blood lactate levels (greater than 5 mmol/L), low pH, an increased anion gap, and increased lactate to pyruvate ratio.

DISCUSSION: A study in 13 healthy subjects receiving a single 1,000 mg dose of metformin 3 hours after a single 800 mg dose of vandetanib resulted in increases in metformin area-under-curve (AUC) of 74% and maximum concentration (Cmax) of 50% with coadministration compared to metformin alone.(1) In a study of normal healthy volunteers, concurrent metformin and oral cimetidine (MATE inhibitor) increased metformin maximum concentration (Cmax) in plasma and whole blood by 60% and increased metformin area-under-curve (AUC) levels in plasma and whole blood by 40%.(1) In a study in 7 subjects, concurrent metformin (250 mg daily) with cimetidine (400 mg twice daily) increased metformin AUC by 50%. Metformin renal clearance over 24 hours was reduced by 27%.(2)

Moderate And Weak Cyp3a4 Inducers/Tacrolimus

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Moderate or weak CYP3A4 inducers may accelerate the metabolism of tacrolimus.(1)

CLINICAL EFFECTS: Concurrent use of a moderate or weak CYP3A4 inducer may result in decreased levels and effectiveness of tacrolimus.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: The manufacturer of tacrolimus recommends monitoring tacrolimus whole blood trough concentrations and adjusting tacrolimus dose if needed. Monitor clinical response closely.(1)

DISCUSSION: A 13-year-old cystic fibrosis patient with a history of liver transplant on stable doses of tacrolimus underwent 2 separate courses of nafcillin therapy (a moderate CYP3A4 inducer). During the 1st course of nafcillin, his tacrolimus levels started to fall 3 days after starting nafcillin, became undetectable at day 8, and recovered to therapeutic levels without a change in tacrolimus dose 5 days after discontinuation of nafcillin. During the 2nd course of nafcillin, tacrolimus level became undetectable 4 days after starting nafcillin and recovered 3 days after stopping nafcillin.(2) Moderate inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 50-80% and include: belzutifan, bosentan, cenobamate, dabrafenib, elagolix, etravirine, lesinurad, lorlatinib, mavacamten, modafinil, nafcillin, repotrectinib, telotristat, and tovorafenib.(3,4) Weak inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 20-50% and include: armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, elafibranor, enasidenib, eslicarbazepine, floxacillin, garlic, genistein, ginseng, glycyrrhizin, meropenem-vaborbactam, nevirapine, oritavancin, omaveloxolone, oxcarbazepine, pioglitazone, relugolix, rufinamide, sulfinpyrazone, sunvozertinib, suzetrigine, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vinblastine, and zanubrutinib.(3,4)

Moderate And Weak Cyp3a4 Inducers/Ubrogepant

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Moderate or weak CYP3A4 inducers may induce the metabolism of ubrogepant.(1)

CLINICAL EFFECTS: Concurrent use of a moderate or weak CYP3A4 inducer may result in decreased levels and effectiveness of ubrogepant.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: The manufacturer recommends a dosage adjustment of ubrogepant when coadministered with moderate or weak CYP3A4 inducers. Initial dose of ubrogepant should be 100 mg. If a second dose is needed, the dose of ubrogepant should be 100 mg.(1)

DISCUSSION: Coadministration of ubrogepant with rifampin, a strong CYP3A4 inducer, resulted in an 80% reduction in ubrogepant exposure. No dedicated drug interaction studies were conducted to assess concomitant use with moderate or weak CYP3A4 inducers. Dose adjustment for concomitant use of ubrogepant with moderate or weak CYP3A4 inducers is recommended based on a conservative prediction of 50% reduction in exposure of ubrogepant.(1) Moderate inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 50-80% and include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, fexinidazole, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pexidartinib, rifabutin, telotristat, thioridazine, and tovorafenib.(2,3) Weak inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 20-50% and include: armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, dexamethasone, dicloxacillin, echinacea, elafibranor, eslicarbazepine, floxacillin, garlic, genistein, ginseng, glycyrrhizin, meropenem-vaborbactam, methylprednisolone, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, relugolix, repotrectinib, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, suzetrigine, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(2,3)

Pioglitazone/Insulin

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: The exact mechanism is unknown, but may be the result of additive fluid retention.(1,2)

CLINICAL EFFECTS: The concurrent use of pioglitazone with insulin may increase the risk of edema and heart failure.(1,2)

PREDISPOSING FACTORS: Specific risk factors for heart failure could not be determined. Patients with ongoing edema are more likely to have edema-associated adverse effects with combination therapy.(1)

PATIENT MANAGEMENT: Patients receiving concurrent therapy should be monitored for cardiovascular adverse events. If signs and symptoms of congestive heart failure develop, patients should be treated according to current standards of care. Consideration should be given to lowering the dosage of or discontinuing pioglitazone.(1,2)

DISCUSSION: In a clinical trial, two of 191 (1.1%) of patients receiving pioglitazone (15 mg) and insulin and two of 188 (1.1%) of patients receiving pioglitazone (30 mg) and insulin developed congestive heart failure. None of the patients receiving insulin alone developed congestive heart failure.(1)

Pioglitazone; Repaglinide; Rosiglitazone/Trimethoprim

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Trimethoprim, a weak CYP2C8 inhibitor, may inhibit the metabolism of pioglitazone,(1,2) repaglinide,(3) and rosiglitazone.(4,5)

CLINICAL EFFECTS: Concurrent use of trimethoprim may result in increased levels of and effects from pioglitazone,(1,2) repaglinide,(3) and rosiglitazone.(4,5)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients receiving concurrent trimethoprim and pioglitazone, repaglinide, or rosiglitazone should be monitored for signs and symptoms of hypoglycemia. The dosage of the antidiabetic agent may need to be adjusted during and following trimethoprim therapy.

DISCUSSION: In a randomized, cross-over study in 16 healthy subjects, trimethoprim (160 mg twice daily for 6 days) increased the area-under-curve (AUC) of a single dose of pioglitazone (15 mg) by 42%.(1) Trimethoprim was shown to inhibit pioglitazone metabolism in vitro in human liver microsomes.(1,2) In a randomized, double-blind, cross-over study in 9 healthy subjects, trimethoprim (160 mg twice daily for 3 days) increased the AUC and maximum concentration (Cmax) of a single dose of repaglinide (0.25 mg) by 61% and 41%, respectively. Trimethoprim also inhibited repaglinide metabolism in vitro in a concentration-dependent manner.(3) In a randomized, cross-over study in 8 healthy subjects, trimethoprim (200 mg twice daily for 5 days) increased the AUC of a single dose of rosiglitazone (8 mg) by 31%. An in vitro study in human liver microsomes showed that trimethoprim inhibited troglitazone metabolism.(4) In a randomized, cross-over study in 10 healthy subjects, trimethoprim (160 mg twice daily for 4 days) increased the AUC of a single dose of troglitazone (4 mg) by 37%.(5)

Selected Antidiabetic Agents/Chloroquine; Hydroxychloroquine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: The exact mechanism is unknown. Chloroquine and hydroxychloroquine may increase insulin sensitivity by inhibiting insulin metabolism and inflammation and increasing cellular uptake of glucose and glycogen synthesis.(1,2) These effects may result in additive hypoglycemia with anti-diabetic agents.

CLINICAL EFFECTS: Concurrent use of chloroquine or hydroxychloroquine and antidiabetic agents may result in severe hypoglycemia.(3) Hypoglycemia can lead to coma.

PREDISPOSING FACTORS: Elderly patients, especially those with decreased renal function may be predisposed to this interaction.

PATIENT MANAGEMENT: Patients maintained on antidiabetic agents who require concurrent therapy with chloroquine or hydroxychloroquine should be closely monitored for hypoglycemia. A decrease in the dose of insulin or other anti-diabetic medications may be required. Patients should be advised of the risk and symptoms of hypoglycemia and to contact their doctor if hypoglycemia occurs.(3) Signs of hypoglycemia may include confusion, dizziness, feeling shaky, unusual hunger, headaches, irritability, pounding heart or very fast pulse, pale skin, sweating, trembling, weakness, or unusual anxiety.

DISCUSSION: Hydroxychloroquine has been shown to cause severe hypoglycemia including loss of consciousness that could be life threatening.(3) Concomitant hypoglycemic agents may increase the risk and/or severity of this effect. A 77 year old man who was stable on twice daily insulin suffered two episodes of hypoglycemic coma 2 weeks after starting prednisone 5 mg daily and hydroxychloroquine 400 mg daily for rheumatoid arthritis. His insulin dosage required a decrease of 37%.(4) Many studies have investigated the glucose-lowering effect of hydroxychloroquine. In a clinical trial of type II diabetics on maximal doses of sulfonylureas, addition of hydroxychloroquine lowered hemoglobin A1C (HbA1C) up to 1% more than placebo.(5) Another clinical trial of type II diabetics on metformin and glimepiride or gliclazide found that hydroxychloroquine 400 mg daily reduced fasting blood glucose (FBG), post-prandial glucose (PPG), and HbA1C to a similar degree as pioglitazone 15 mg daily at 24 weeks.(6) In a prospective observational study, 250 uncontrolled type II diabetics on metformin, glimepiride, pioglitazone, sitagliptin, and a SGLT-2 inhibitor received hydroxychloroquine 400 mg daily for 48 weeks. HbA1C decreased from 8.83% to 6.44%, FBG decreased by 40.78%, and PPG decreased by 58.95%. The doses of metformin were reduced by 50%, glimepiride and sitagliptin by 75%, and SGLT-2 inhibitors were discontinued in most patients.(7)

Selected Antidiabetic Agents/Selected Quinolones

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: The exact mechanism is unknown.

CLINICAL EFFECTS: Concurrent use of quinolones and antidiabetic agents may result in severe hypoglycemia.(1-7) Hypoglycemia can lead to coma.

PREDISPOSING FACTORS: Elderly patients, especially those with decreased renal function may be predisposed to this interaction.(5)

PATIENT MANAGEMENT: Patients maintained on antidiabetic agents who require concurrent therapy with a quinolone should be closely monitored for hypoglycemia.(1-4) Patients should be instructed to discontinue quinolone use and contact their doctor if hypoglycemia occurs.(2,4) Signs of hypoglycemia may include confusion, dizziness, feeling shaky, unusual hunger, headaches, irritability, pounding heart or very fast pulse, pale skin, sweating, trembling, weakness, or unusual anxiety.

DISCUSSION: Hypoglycemia has been reported with concurrent ciprofloxacin and glyburide,(1,8,9) levofloxacin and glyburide,(2,10,11) norfloxacin and glyburide,(3) levofloxacin and glipizide (12) as well as levofloxacin and metformin-glibenclamide.(14) There has been one report of fatal hypoglycemia with concurrent levofloxacin and glyburide(9) and one of the above reports of hypoglycemia with concurrent levofloxacin and glyburide resulted in hypoxic brain injury.(11) A review of postmarketing adverse event data for the fluoroquinolones and hypoglycemic coma identified 56 reports in FAERS search from October 1987- April 2017 and 11 additional cases in the medical literature. Most patients had risk factors for hypoglycemia. 41 patients were taking one or more hypoglycemic drugs. 13 deaths occurred (some of these patients had renal insufficiency). 9 patients did not fully recover and had resultant disability.(13)

Selected Cyp2c8 Substrates/Leflunomide; Teriflunomide

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Teriflunomide may inhibit the metabolism of agents metabolized by CYP2C8. Leflunomide is metabolized to teriflunomide and recommended dosages of both products produce similar levels of teriflunomide.(1)

CLINICAL EFFECTS: Concurrent use of leflunomide or teriflunomide may result in elevated levels of and toxicity from agents metabolized by CYP2C8, such as pioglitazone, repaglinide, or rosiglitazone.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients receiving concurrent therapy with leflunomide or teriflunomide and an agent metabolized by CYP2C8 should be closely monitored. The dosage of the CYP2C8 substrate may need to be adjusted if leflunomide or teriflunomide are initiated.(1) Because of teriflunomide's slow elimination, the effects of teriflunomide on these CYP2C8 substrates may persist for some time without the use of cholestyramine or activated charcoal to increase teriflunomide elimination.(1)

DISCUSSION: Concurrent teriflunomide increased the maximum concentration (Cmax) and area-under-curve (AUC) of repaglinide (0.25 mg single dose) by 1.7-fold and 2.4-fold, respectively.(1) Leflunomide is metabolized to teriflunomide and recommended dosages of both products produce similar levels of teriflunomide.(1) CYP2C8 substrates include pioglitazone, repaglinide, or rosiglitazone.(1,2)

Selected Moderate-Weak Cyp3a4 Inducers/Exemestane

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: CYP3A4 inducers may induce the metabolism of exemestane.(1)

CLINICAL EFFECTS: Concurrent use of a CYP3A4 inducer may result in decreased levels and effectiveness of exemestane.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: The US manufacturer of exemestane recommends that patients receiving concurrent therapy with a strong CYP3A4 inducer receive 50 mg of exemestane daily after a meal.(1) It may be prudent to consider a dosage increase for patients receiving weaker CYP3A4 inducers.

DISCUSSION: In a study in 10 healthy postmenopausal subjects, pretreatment with rifampin (a strong CYP3A4 inducer, 600 mg daily for 14 days) decreased the area-under-curve (AUC) and maximum concentration (Cmax) of a single dose of exemestane (25 mg) by 54% and 41%, respectively.(1) Strong inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 80% or more and include: carbamazepine, enzalutamide, mitotane, phenobarbital, phenytoin, rifabutin, rifampin, and St. John's wort.(1-3) Moderate inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 50-80% and include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, fexinidazole, lesinurad, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, rifabutin, sotorasib, telotristat ethyl, thioridazine, and tovorafenib.(2,3) Weak inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 20-50% and include: armodafinil, aumolertinib, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, elafibranor, enasidenib, eslicarbazepine, floxacillin, garlic, gingko, ginseng, glycyrrhizin, lorlatinib, meropenem-vaborbactam, methylprednisolone, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, suzetrigine, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(2,3)

Thiazolidinedione Antidiabetics/Pregabalin

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Both pregabalin and thiazolidinedione antidiabetics may cause weight gain and/or fluid retention.(1)

CLINICAL EFFECTS: Concurrent use of pregabalin and thiazolidinedione antidiabetics may result in weight gain and/or fluid retention, which may increase the risk of heart failure in patients with preexisting cardiac conditions.(1)

PREDISPOSING FACTORS: Preexisting cardiac conditions may increase the risk of heart failure.(1)

PATIENT MANAGEMENT: Patients should be monitored for weight gain and/or fluid retention when taking pregabalin with the thiazolidinedione antidiabetics agents together. Congestive heart failure or worsening of existing congestive heart failure may occur.

DISCUSSION: In clinical trials, the incidence of peripheral edema was 3% of patients receiving a thiazolidinedione antidiabetic alone, 8% of patients receiving pregabalin alone, and 19% of patients on combination therapy. The incidence of weight gain was 0% of patients receiving a thiazolidinedione antidiabetic alone, 4% of patients receiving pregabalin alone, and 7.5% of patients on combination therapy.(1)

Weak Cyp3a4 Inducers/Atogepant

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Weak CYP3A4 inducers may increase the metabolism of atogepant by CYP3A4.(1)

CLINICAL EFFECTS: The concurrent use of weak CYP3A4 inducers with atogepant may result in decreased levels and clinical effectiveness of atogepant.(1)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: The manufacturer of atogepant recommends that patients on concomitant weak CYP3A4 inducers receive atogepant 30 mg or 60 mg once daily for prevention of episodic migraines and receive atogepant 60 mg once daily for prevention of chronic migraines.(1) Patients receiving concurrent therapy with CYP3A4 inducers and atogepant should be observed for decreased clinical effectiveness.

DISCUSSION: In a study of healthy subjects, rifampin, a strong CYP3A4 inducer, decreased the area-under-curve (AUC) and maximum concentration (Cmax) of atogepant by 60% and 30%, respectively. Topiramate, a weak CYP3A4 inducer, decreased atogepant AUC and Cmax by 25% and 24%, respectively.(1) Weak CYP3A4 inducers linked to this monograph include: armodafinil, aumolertinib, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, eslicarbazepine, floxacillin, garlic, genistein, ginseng, glycyrrhizin, methylprednisolone, mobocertinib, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(1,2)

*Acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma.

*Severe renal impairment (estimated glomerular filtration rate (eGFR) <30 mL/minute per 1.73 m2).

*Known hypersensitivity to metformin hydrochloride.

*Initiation in patients with established New York Heart Association (NYHA) class III or IV heart failure (HF).

*Known serious hypersensitivity reaction to pioglitazone or any ingredient in the formulation.

• Acute decompensated heart failure
• Alcohol intoxication
• Alcohol use disorder
• Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
• Chronic kidney disease stage 5 (failure) GFr<15 ml/min
• Dehydration
• Malignant tumor of urinary bladder
• Metabolic acidosis
• Mitochondrial disease
• Sepsis
• Shock

• Acute decompensated heart failure
• Acute myocardial infarction
• Chronic heart failure
• Chronic kidney disease stage 3B (moderate) GFR 30-44 ml/min
• Disease of liver
• Hematuria
• Hypoglycemic disorder
• Kidney disease with likely reduction in glomerular filtration rate (GFr)
• Severe diarrhea
• Severe hypoxemia
• Severe vomiting

• Debilitation
• Disease of liver
• Edema
• Fever
• Fracture
• Hypothyroidism
• Infection
• Macular retinal edema
• Vitamin b12 deficiency

The most common adverse effects of immediate-release metformin hydrochloride tablets (>5%) are diarrhea, nausea/vomiting, flatulence, asthenia, indigestion, abdominal discomfort, and headache.

The most common adverse effects of metformin hydrochloride oral solution are diarrhea, nausea/vomiting, flatulence, asthenia, indigestion, abdominal discomfort, and headache.

The most common adverse effects of extended-release metformin hydrochloride tablets (>5%) are diarrhea, nausea/vomiting, flatulence, asthenia, indigestion, abdominal discomfort, and headache.

The most common adverse effects of pioglitazone (>=5% of patients) reported in clinical trials were upper respiratory tract infection, headache, sinusitis, myalgia, and pharyngitis.

Less Frequent

• Body fluid retention
• Dyspnea
• Edema
• Weight gain

Rare or Very Rare

• Abnormal hepatic function tests
• Abnormal hepatic function tests
• Acute respiratory distress syndrome
• Autoimmune hemolytic anemia
• Autoimmune hepatitis
• Cholestatic hepatitis
• Fracture
• Heart failure
• Hepatic failure
• Hepatitis
• Hepatocellular damage
• Hypoglycemic disorder
• Lactic acidosis
• Macular retinal edema
• Malignant tumor of urinary bladder
• Megaloblastic anemia
• Ovulation stimulation
• Pancreatitis
• Worsening of chronic heart failure

More Frequent

• Abdominal distension
• Diarrhea
• Dizziness
• Dysgeusia
• Flatulence
• Flatulence
• Headache disorder
• Headache disorder
• Myalgia
• Nausea
• Pharyngitis
• Sinusitis
• Upper respiratory infection
• Upper respiratory infection
• Urinary tract infection
• Vitamin b12 deficiency
• Vomiting
• Weight loss

Less Frequent

• Acute abdominal pain
• Chills
• Constipation
• Diarrhea
• Dizziness
• Dyspepsia
• Flu-like symptoms
• Flushing
• General weakness
• Hyperhidrosis
• Hypoglycemic disorder
• Myalgia
• Nail disorders
• Palpitations
• Rhinitis

Rare or Very Rare

• Anticholinergic toxicity
• Drowsy
• Pruritus of skin
• Skin rash
• Urticaria

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Safety and effectiveness of immediate-release metformin hydrochloride tablets and oral solution have been established in pediatric patients 10--16 years of age. Safety and effectiveness of immediate-release metformin hydrochloride tablets and oral solution have not been established in pediatric patients <10 years of age. Use of immediate-release metformin hydrochloride tablets and oral solution is supported by evidence from adequate and well-controlled studies in adults with additional data from a controlled clinical study in pediatric patients 10--16 years of age with type 2 diabetes mellitus, which demonstrated a similar response in glycemic control to that seen in adults. In this study, adverse effects were similar to those described in adults. A maximum daily dosage of 2 g of immediate-release metformin hydrochloride tablets or oral solution is recommended.

Safety and effectiveness of extended-release metformin hydrochloride tablets in pediatric patients have not been established.

Safety and efficacy of pioglitazone have not been established in children or adolescents younger than 18 years of age; use in this age group currently is not recommended by the manufacturer because of adverse effects observed in adults (e.g., fluid retention and HF, fractures, urinary bladder tumors).

Limited data with metformin hydrochloride in pregnant females are not sufficient to determine a medication-associated risk for major birth defects or miscarriage. Available studies have not reported a clear association with metformin and major birth defects, miscarriage, or adverse maternal or fetal outcomes. Limited data from uncontrolled or retrospective studies are conflicting with regard to the effects of long-term maternal therapy with metformin hydrochloride (1.5-3 g daily) on neonatal morbidity (e.g., congenital malformations) and mortality.

Reproduction studies in rats and rabbits given metformin hydrochloride dosages of 600 mg/kg daily (about twice the maximum recommended human daily dosage based on body surface area or about 3 and 6 times the maximum recommended human daily dosage of extended-release tablets (2 g) based on body surface area comparisons with rats and rabbits, respectively) have not revealed evidence of harm (e.g., teratogenicity) to the fetus. Determination of fetal concentrations of metformin suggest that a partial placental barrier to the medication exists.

Poorly controlled diabetes mellitus in pregnancy increases the maternal risk for diabetic ketoacidosis, pre-eclampsia, spontaneous abortions, preterm delivery, and delivery complications. Poorly controlled diabetes mellitus increases the fetal risk for major birth defects, stillbirth, and macrosomia-related morbidity. Since abnormal maternal blood glucose concentrations during pregnancy may be associated with a higher incidence of congenital abnormalities, most experts recommend that insulin be used during pregnancy to maintain optimum control of blood glucose concentration.

There is insufficient evidence with pioglitazone in pregnant women to evaluate a drug-associated risk for major birth defects or miscarriage. In reproduction studies in rats and rabbits, pioglitazone administered during organogenesis at exposures up to 5 and 35 times the maximum recommended human dose, respectively, was not associated with adverse developmental effects. However, delayed parturition and reduced embryofetal viability were observed with pioglitazone dosages at least 9 times the maximum recommended human dose. Offspring of pregnant rats who were administered pioglitazone at dosages at least 2 times the maximum recommended human dose during late gestation and lactation had delayed postnatal development attributed to decreased body weight.

Poorly controlled diabetes during pregnancy increases the risk for diabetic ketoacidosis, pre-eclampsia, spontaneous abortions, preterm delivery, still birth, delivery complications, major birth defects, and macrosomia related morbidity.

Metformin is distributed into milk in lactating rats. Limited data indicate that metformin is distributed into breast milk in humans. However, there is insufficient information to determine the effects of metformin on the breast-fed infant and no available information on the effects of metformin on milk production.

Published clinical lactation studies report that metformin present in human milk resulted in infant doses approximately 0.11--1% of the maternal weight-adjusted dosage and a milk/plasma ratio ranging between 0.13 and 1. However, these studies were not designed to establish the risk of metformin use during lactation; limited adverse event data were collected in infants. In a study in 7 nursing females who received metformin hydrochloride (median dosage 1500 mg daily), the mean milk-to-plasma ratio for metformin was 0.35 and the overall average concentration in milk over the dosing interval was 0.27 mg/L. Metformin was present in low or undetectable amounts in the plasma of 4 breast-fed infants, and no adverse effects were noted in 6 infants that were evaluated. In another study, mean peak and trough metformin concentrations in 4 nursing women receiving metformin hydrochloride 500 mg twice daily were 1.06 and 0.42 mcg/mL, respectively, in serum and 0.42 and 0.39 mcg/mL, respectively, in breast milk. The mean milk-to-serum ratio was 0.63 and the mean estimated infant dose as a percentage of the mother's weight-adjusted dose was 0.65%. Blood glucose concentrations obtained in 3 infants 4 hours after breastfeeding were within normal limits (47-77 mg/dL).

The developmental and health benefits of breastfeeding should be considered along with mother's clinical need for the medication and potential adverse effects on the breast-fed child (e.g., hypoglycemia). Breast-fed infants should be monitored for signs of hypoglycemia (e.g., jitters, cyanosis, apnea, hypothermia, excessive sleepiness, poor feeding, seizures).

There are no data on the presence of pioglitazone in human milk, the effects on the breast-fed infant, or the effects on milk production. Pioglitazone is distributed into milk in rats. The benefits of breast-feeding should be weighed against the potential risk of adverse effects on the breast-fed infant from pioglitazone.

Metformin should be used with caution in geriatric patients since aging is associated with a greater frequency of reduced renal, hepatic, and cardiac function, and of concomitant disease or other therapy, resulting in a higher risk of lactic acidosis. Initial dosages of metformin hydrochloride in geriatric patients should be conservative (initiated at the low end of the dosage range) and should be titrated carefully; limited data suggest reducing dosage by approximately 33% in geriatric patients. In addition, renal function should be monitored more frequently in geriatric patients to determine the appropriate dosage of metformin hydrochloride. Any dosage adjustment in geriatric patients should be based on a careful assessment of renal function.

Controlled clinical trials evaluating metformin hydrochloride immediate-release and extended-release tablets did not include sufficient numbers of geriatric patients to determine whether geriatric patients respond differently to metformin than younger patients, although other reported clinical experience has not identified any differences in response between geriatric and younger patients.

In general, dosage selection for a geriatric patient should be cautious, usually starting at the low end of the dosage range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other medication therapy and the higher risk of lactic acidosis. In addition, renal function should be monitored more frequently in geriatric patients and care should be taken in dosage selection; such patients generally should not receive the maximum recommended dosage of metformin hydrochloride.

Pharmacokinetic, efficacy, and adverse effect profiles in geriatric patients are similar to those in younger adults, although small sample sizes in studies of patients 75 years or older limit conclusions. While pioglitazone AUC is about 21% higher in healthy geriatric individuals than in younger individuals and mean terminal half-life is also prolonged (10 versus 7 hours, respectively), these changes are not considered clinically relevant.