Allergy Relief (cetirizine HCl)

The manufacturer states that patients 12 years of age or older who have impaired renal function (e.g., creatinine clearance of 11-31 mL/minute) or hepatic impairment or who are undergoing hemodialysis (creatinine clearance of less than 7 mL/minute), should receive a cetirizine hydrochloride dosage of 5 mg daily. The manufacturer also states that children 6-11 years of age with impaired renal or hepatic function should use the lower recommended dosage (5 mg once daily). The manufacturer states that use of cetirizine hydrochloride in children younger than 6 years of age with impaired renal or hepatic function is not recommended because administration of doses smaller than 2.5 mg is difficult and not reliable, and pharmacokinetic data are lacking in this patient population.

When extended-release tablets of cetirizine hydrochloride in fixed combination with pseudoephedrine hydrochloride are used in patients 12 years of age or older who have impaired renal function (i.e., creatinine clearance of 11-31 mL/minute) or hepatic impairment or who are undergoing hemodialysis (creatinine clearance of less than 7 mL/minute), the recommended cetirizine hydrochloride dosage is 5 mg once daily.

Cetirizine is administered orally. Cetirizine oral solution (syrup) should be administered using the measuring device (i.e., cup) provided by the manufacturer. Cetirizine chewable tablets may be administered with or without water. Tablets containing cetirizine hydrochloride in fixed combination with pseudoephedrine hydrochloride should be swallowed intact and patients should be instructed not to break or chew such tablets.

The manufacturer states that the time of administration of cetirizine may be adjusted for individual patient requirements. Although food may decrease peak plasma concentrations of cetirizine and lengthen the time to achievement of peak plasma concentrations, the manufacturer states that cetirizine may be administered without regard to food because food does not affect the extent of absorption of the drug when administered as conventional or chewable tablets.

The oral bioavailability of cetirizine hydrochloride conventional tablets is comparable to that of the oral solution and to that of the chewable tablets (administered with or without water).

Because cetirizine is metabolized only minimally in the liver and is excreted mainly unchanged in urine, the drug may have a low potential for adverse drug interactions associated with metabolic enzyme systems.

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

Selected Antihistamines/Selected Maois

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: MAOIs prolong and intensify the effects of antihistamines.(1-6)

CLINICAL EFFECTS: Concurrent use of antihistamines and a MAOI may result in severe hypotension.(1-6)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of antihistamines and a MAOI is contraindicated.(1-6)

DISCUSSION: MAOIs may prolong and intensify the effects of antihistamines, resulting in severe hypotension.(1-6) A case report describes a patient having cyproheptadine added to their phenelzine therapy in an attempt to relieve the patients anorgasmia. The patient began to suddenly experience visual hallucination after taking the cyproheptadine for two months. Once the medication was terminated, the hallucinations stopped occurring within 48 hours.(7) Methylene blue, when administered intravenously, has been shown to reach sufficient concentrations to be a potent inhibitor of MAO-A.(8,9)

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

Agents That Affect Iodide/Radioactive Iodide

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

MECHANISM OF ACTION: Many compounds can affect iodide protein binding and alter iodide pharmacokinetics and pharmacodynamics.(1)

CLINICAL EFFECTS: Compounds that affect iodide pharmacokinetics and pharmacodynamics may impact the effectiveness of radioactive iodide.(1)

PREDISPOSING FACTORS: Compounds that affect iodide pharmacokinetics and pharmacodynamics are expected to have the most impact during therapy using radioactive iodide. Diagnostic procedures would be expected to be impacted less.

PATIENT MANAGEMENT: Discuss the use of agents that affect iodide pharmacokinetics and pharmacodynamics with the patient's oncologist.(1) Because indocyanine green contains sodium iodide, the iodine-binding capacity of thyroid tissue may be reduced for at least one week following administration. Do not perform radioactive iodine uptake studies for at least one week following administration of indocyanine green.(2) The manufacturer of iopamidol states administration may interfere with thyroid uptake of radioactive iodine and decrease therapeutic and diagnostic efficacy. Avoid thyroid therapy or testing for up to 6 weeks post administration of iopamidol.(3)

DISCUSSION: Many agents interact with radioactive iodine. The average duration of effect is: anticoagulants - 1 week antihistamines - 1 week anti-thyroid drugs, e.g: carbimazole, methimazole, propylthiouracil - 3-5 days corticosteroids - 1 week iodide-containing medications, e.g: amiodarone - 1-6 months expectorants - 2 weeks Lugol solution - 3 weeks saturated solution of potassium iodine - 3 weeks vitamins - 10-14 days iodide-containing X-ray contrast agents - up to 1 year lithium - 4 weeks phenylbutazone - 1-2 weeks sulfonamides - 1 week thyroid hormones (natural or synthetic), e.g.: thyroxine - 4 weeks tri-iodothyronine - 2 weeks tolbutamide - 1 week topical iodide - 1-9 months (1)

Agents That Affect Iodide/Sodium Iodide I 131

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

MECHANISM OF ACTION: Many compounds can affect iodide protein binding and alter iodide pharmacokinetics and pharmacodynamics.(1,2)

CLINICAL EFFECTS: Compounds that affect iodide pharmacokinetics and pharmacodynamics may impact the effectiveness of radioactive iodide.(1,2)

PREDISPOSING FACTORS: Compounds that affect iodide pharmacokinetics and pharmacodynamics are expected to have the most impact during therapy using radioactive iodide. Diagnostic procedures would be expected to be impacted less.

PATIENT MANAGEMENT: Discuss the use of agents that affect iodide pharmacokinetics and pharmacodynamics with the patient's oncologist.(1,2) Because indocyanine green contains sodium iodide, the iodine-binding capacity of thyroid tissue may be reduced for at least one week following administration. Do not perform radioactive iodine uptake studies for at least one week following administration of indocyanine green.(3) The manufacturer of iopamidol states administration may interfere with thyroid uptake of radioactive iodine and decrease therapeutic and diagnostic efficacy. Avoid thyroid therapy or testing for up to 6 weeks post administration of iopamidol.(4)

DISCUSSION: Many agents interact with radioactive iodine. The average duration of effect is: anticoagulants - 1 week antihistamines - 1 week anti-thyroid drugs, e.g: carbimazole, methimazole, propylthiouracil - 3-5 days corticosteroids - 1 week iodide-containing medications, e.g: amiodarone - 1-6 months expectorants - 2 weeks Lugol solution - 3 weeks saturated solution of potassium iodine - 3 weeks vitamins - 10-14 days iodide-containing X-ray contrast agents - up to 1 year lithium - 4 weeks phenylbutazone - 1-2 weeks sulfonamides - 1 week thyroid hormones (natural or synthetic), e.g.: thyroxine - 4 weeks tri-iodothyronine - 2 weeks tolbutamide - 1 week topical iodide - 1-9 months (1,2)

Anticholinergics/Clozapine

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

MECHANISM OF ACTION: Clozapine has potent anticholinergic properties and inhibits serotonin receptors, including 5-HT3.(1-4) Both of these properties may cause inhibition of gastrointestinal (GI) smooth muscle contraction, resulting in decreased peristalsis.(3,4) These effects may be compounded by concurrent use of anticholinergic agents.(1-6)

CLINICAL EFFECTS: Concurrent use of clozapine with other anticholinergic agents may increase the risk of constipation (common) and serious bowel complications (uncommon), including complete bowel obstruction, fecal impaction, paralytic ileus and intestinal ischemia or infarction.(1-6)

PREDISPOSING FACTORS: The risk for serious bowel complications is higher with increasing age, higher frequency of constipation, and in patients on higher doses of clozapine or multiple anticholinergic agents.(1,5)

PATIENT MANAGEMENT: Avoid the use of other anticholinergic agents with clozapine.(1-6) If concurrent use is necessary, evaluate the patient's bowel function regularly. Monitor for symptoms of constipation and GI hypomotility, including having bowel movements less than three times weekly or less than usual, difficulty having a bowel movement or passing gas, nausea, vomiting, and abdominal pain or distention.(2) Consider a prophylactic laxative in those with a history of constipation or bowel obstruction.(2) Review patient medication list for other anticholinergic agents. When possible, decrease the dosage or number of prescribed anticholinergic agents, particularly in the elderly. Counsel the patient about the importance of maintaining adequate hydration. Encourage regular exercise and eating a high-fiber diet.(2)

DISCUSSION: In a prospective cohort study of 26,720 schizophrenic patients in the Danish Central Psychiatric Research Registry, the odds ratio (OR) for ileus was 1.99 with clozapine and 1.48 with anticholinergics. The OR for fatal ileus was 6.73 with clozapine and 5.88 with anticholinergics. Use of anticholinergics with 1st generation antipsychotics (FGA) increased the risk of ileus compare to FGA alone, but this analysis was not done with clozapine.(5) A retrospective cohort study of 24,970 schizophrenic patients from the Taiwanese National Health Insurance Research Database found that the hazard ratio (HR) for clozapine-induced constipation increased from 1.64 when clozapine is used alone, to 2.15 when used concomitantly with anticholinergics. However, there was no significant difference in the HR for ileus when clozapine is used with and without anticholinergics (1.95 and 2.02, respectively).(6) In the French Pharmacovigilance Database, 7 of 38 cases of antipsychotic-associated ischemic colitis or intestinal necrosis involved clozapine, and 5 of these cases involved use of concomitant anticholinergic agents. Three patients died, one of whom was on concomitant anticholinergics.(3) In a case series, 4 of 9 cases of fatal clozapine-associated GI dysfunction involved concurrent anticholinergic agents.(4)

Anticholinergics/Glucagon (Diagnostic)

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

MECHANISM OF ACTION: Glucagon and anticholinergic agents may have additive effects on inhibition of gastrointestinal motility.(1)

CLINICAL EFFECTS: Concurrent use of glucagon with anticholinergic agents may increase the risk of gastrointestinal hypomotility, including constipation and bowel complications.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of glucagon as a diagnotic aid is not recommended with the use of anticholinergic agents.(1) If concurrent use is necessary, evaluate the patient's bowel function. Monitor for symptoms of constipation and gastrointestinal hypomotility.

DISCUSSION: Both glucagon and anticholinergic agents may have additive effects on inhibition of gastrointestinal motility and increase the risk of gastrointestinal adverse effects.(1)

Anticholinergics/Solid Oral Potassium Capsules

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

MECHANISM OF ACTION: Concentrated potassium may damage the lining of the GI tract. Anticholinergics delay gastric emptying, resulting in the potassium product remaining in the gastrointestinal tract for a longer period of time.(1-16))

CLINICAL EFFECTS: Use of solid oral dosage forms of potassium in patients treated with anticholinergics may result in gastrointestinal erosions, ulcers, stenosis and bleeding.(1-16)

PREDISPOSING FACTORS: Diseases or conditions which may increase risk for GI damage include: preexisting dysphagia, strictures, cardiomegaly, diabetic gastroparesis, elderly status, or insufficient oral intake to allow dilution of potassium.(1-10,21) Other drugs which may add to risk for GI damage include: nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates, or tetracyclines.(21)

PATIENT MANAGEMENT: Regulatory agency and manufacturer recommendations regarding this interaction: - In the US, all solid oral dosage forms (including tablets and extended release capsules) of potassium are contraindicated in patients receiving anticholinergics at sufficient dosages to result in systemic effects.(2-8) Patients receiving such anticholinergic therapy should use a liquid form of potassium chloride.(2) - In Canada, solid oral potassium is contraindicated in any patient with a cause for arrest or delay in tablet/capsule passage through the gastrointestinal tract and the manufacturers recommend caution with concurrent anticholinergic medications.(1,9-10) Evaluate each patient for predisposing factors which may increase risk for GI damage. In patients with multiple risk factors for harm, consider use of liquid potassium supplements, if tolerated. For patients receiving concomitant therapy, assure any potassium dose form is taken after meals with a large glass of water or other fluid. To decrease potassium concentration in the GI tract, limit each dose to 20 meq; if more than 20 meq daily is required, give in divided doses.(2) If concurrent therapy is warranted, monitor patients receiving concurrent therapy for signs of blood loss, including decreased hemoglobin, hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. Patients should be instructed to immediately report any difficulty swallowing, abdominal pain, distention, severe vomiting, or gastrointestinal bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling.

DISCUSSION: In clinical trials, there was a higher incidence of gastric and duodenal lesions in patients receiving a high dose of a wax-matrix controlled-release formulation with a concurrent anticholinergic agent. The lesions were asymptomatic and not accompanied by bleeding, as shown by a lack of positive Hemoccult tests.(1-17) Several studies suggest that the incidence of gastric and duodenal lesions may be less with the microencapsulated formulation of potassium chloride.(14-17)

Anticholinergics/Solid Oral Potassium Tablets

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

MECHANISM OF ACTION: Concentrated potassium may damage the lining of the GI tract. Anticholinergics delay gastric emptying, resulting in the potassium product remaining in the gastrointestinal tract for a longer period of time.(1-16)

CLINICAL EFFECTS: Use of solid oral dosage forms of potassium in patients treated with anticholinergics may result in gastrointestinal erosions, ulcers, stenosis and bleeding.(1-16)

PREDISPOSING FACTORS: Diseases or conditions which may increase risk for GI damage include: preexisting dysphagia, strictures, cardiomegaly, diabetic gastroparesis, elderly status, or insufficient oral intake to allow dilution of potassium.(1-10,21) Other drugs which may add to risk for GI damage include: nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates, or tetracyclines.(21)

PATIENT MANAGEMENT: Regulatory agency and manufacturer recommendations regarding this interaction: - In the US, all solid oral dosage forms (including tablets and extended release capsules) of potassium are contraindicated in patients receiving anticholinergics at sufficient dosages to result in systemic effects.(2-8) Patients receiving such anticholinergic therapy should use a liquid form of potassium chloride.(2) - In Canada, solid oral potassium is contraindicated in any patient with a cause for arrest or delay in tablet/capsule passage through the gastrointestinal tract and the manufacturers recommend caution with concurrent anticholinergic medications.(1,9-10) Evaluate each patient for predisposing factors which may increase risk for GI damage. In patients with multiple risk factors for harm, consider use of liquid potassium supplements, if tolerated. For patients receiving concomitant therapy, assure any potassium dose form is taken after meals with a large glass of water or other fluid. To decrease potassium concentration in the GI tract, limit each dose to 20 meq; if more than 20 meq daily is required, give in divided doses.(2) If concurrent therapy is warranted, monitor patients receiving concurrent therapy for signs of blood loss, including decreased hemoglobin, hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. Patients should be instructed to immediately report any difficulty swallowing, abdominal pain, distention, severe vomiting, or gastrointestinal bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling.

DISCUSSION: In clinical trials, there was a higher incidence of gastric and duodenal lesions in patients receiving a high dose of a wax-matrix controlled-release formulation with a concurrent anticholinergic agent. Some lesions were asymptomatic and not accompanied by bleeding, as shown by a lack of positive Hemoccult tests.(1-17) Several studies suggest that the incidence of gastric and duodenal lesions may be less with the microencapsulated formulation of potassium chloride.(14-17)

Anticholinergics; Opioids/Eluxadoline

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

MECHANISM OF ACTION: Eluxadoline is a mixed mu-opioid and kappa-opioid agonist and delta-opioid antagonist and may alter or slow down gastrointestinal transit.(1)

CLINICAL EFFECTS: Constipation related adverse events that sometimes required hospitalization have been reported, including the development of intestinal obstruction, intestinal perforation, and fecal impaction.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid use with other drugs that may cause constipation. If concurrent use is necessary, evaluate the patient's bowel function regularly. Monitor for symptoms of constipation and GI hypomotility, including having bowel movements less than three times weekly or less than usual, difficulty having a bowel movement or passing gas, nausea, vomiting, and abdominal pain or distention.(1) Instruct patients to stop eluxadoline and immediately contact their healthcare provider if they experience severe constipation. Loperamide may be used occasionally for acute management of severe diarrhea, but must be discontinued if constipation develops.(1)

DISCUSSION: In phase 3 clinical trials, constipation was the most commonly reported adverse reaction (8%). Approximately 50% of constipation events occurred within the first 2 weeks of treatment while the majority occurred within the first 3 months of therapy. Rates of severe constipation were less than 1% in patients receiving eluxadoline doses of 75 mg and 100 mg.(1)

Selected Steroids/Antiretroviral Cyp3a4 Inhibitors

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

MECHANISM OF ACTION: Antiretroviral CYP3A4 inhibitors may inhibit the metabolism of corticosteroids metabolized by CYP3A4. Dexamethasone may induce metabolism of agents that are substrates of CYP3A4.(1-13,50)

CLINICAL EFFECTS: Concurrent use of antiretroviral CYP3A4 inhibitors may result in increased systemic exposure to and effects from corticosteroids metabolized by CYP3A4, including Cushing's syndrome and adrenal suppression. Concurrent dexamethasone may result in decreased levels and effectiveness of CYP3A4 substrates.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: If possible, avoid concurrent therapy of corticosteroids metabolized by CYP3A4 with antiretroviral CYP3A4 inhibitors. Alternative corticosteroids that are less affected by CYP3A4 inhibitors should be considered, like beclomethasone, prednisone, and prednisolone. If concurrent therapy is warranted, patients should be closely monitored for systemic effects. The corticosteroid may need to be discontinued. Patients receiving concurrent therapy with dexamethasone and substrates of CYP3A4 should also be monitored for decreased effectiveness of the CYP3A4 substrate. The manufacturers of nasal fluticasone(14-16) and fluticasone for inhalation(17) state that concurrent use of fluticasone and atazanavir, indinavir, nelfinavir, ritonavir or saquinavir is not recommended. The US manufacturers of atazanavir,(1) fosamprenavir,(5) indinavir(6) and nelfinavir(8) recommend caution with concurrent use of inhaled or nasal fluticasone. Consider alternatives to fluticasone if long-term use is required.

DISCUSSION: In a study, boceprevir (800 mg TID for 7 days) increased the area-under-curve (AUC) of a single dose of prednisone (40 mg) by 22%. The maximum concentration (Cmax) and AUC of prednisolone increased by 16% and 37%, respectively.(2) A study of 14 healthy adults found that concurrent use of ketoconazole with ciclesonide increased the AUC of ciclesonide's active metabolite, des-ciclesonide, by approximately 3.6-fold at steady state, while levels of ciclesonide remained unchanged. However, the study concluded that no dosage adjustments were required because ciclesonide has a very low potential to cause side effects.(18) A study in 18 healthy subjects examined the effects of ritonavir (100 mg twice daily) on fluticasone nasal spray (200 mcg daily). In most subjects, fluticasone was undetectable (<10 pg/ml) when administered alone. In subjects in whom fluticasone was detectable when given alone, Cmax and area-under-curve AUC averaged 11.9 pg/ml and 8.43 pg x hr/ml, respectively. With concurrent ritonavir, fluticasone Cmax and AUC increased to 318 pg/ml and 3102.6 pg x hr/ml, respectively.(7,11,14) This reflects increases in Cmax and AUC by 25-fold and 350-fold, respectively.(3) The cortisol AUC decreased by 86%.(6,14-16) In a study in 10 healthy subjects, ritonavir (200 mg twice daily for 4 and 14 days) increased the AUC of a single dose of prednisolone by 1.41-fold and 1.30-fold, respectively, after 4 days and 14 days of ritonavir.(19) There have been several case reports of Cushing's syndrome in patients treated concurrently with ritonavir and inhaled budesonide,(19-20) dexamethasone,(22) injectable triamcinolone,(23-26) nasal fluticasone.(28-46) Hepatitis has also been reported with concurrent budesonide and ritonavir.(47) In a study in 9 healthy subjects, mibefradil (50 mg once daily for 3 days) increased the AUC, Cmax, and elimination half-life of methylprednisolone by 3.8-fold, 1.8-fold, and 2.7-fold, respectively.(48) In a study in 8 healthy subjects, following nefazodone administration the following changes were seen with methylprednisolone: mean (+/-SD) area under the concentration-time curve was significantly higher (1393 +/- 343 vs. 2966 +/- 928 ug*h/L; P < 0.005), apparent clearance was lower (28.7 +/- 7.2 vs. 14.6 +/- 7.8 L/h; P < 0.02) and the terminal elimination half-life was longer (2.28 +/- 0.49 vs. 3.32 +/- 0.95 hours; P < 0.02).(49) Selected steroids metabolized by CYP3A4 are linked to this monograph.(50) Selected CYP3A4 inhibitors and substrates linked to this monograph include: atazanavir, cobicistat, darunavir, fosamprenavir, indinavir, lenacapavir, lopinavir, nelfinavir, saquinavir, and tipranavir.(50)

Selected Steroids/Selected Strong Cyp3a4 Inhibitors

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

MECHANISM OF ACTION: Strong CYP3A4 inhibitors may inhibit the metabolism of corticosteroids metabolized by CYP3A4.

CLINICAL EFFECTS: Concurrent use of strong CYP3A4 inhibitors may result in increased systemic exposure to and effects from corticosteroids metabolized by CYP3A4, including Cushing's syndrome and adrenal suppression.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: If possible, avoid concurrent therapy between corticosteroids metabolized by CYP3A4 and strong CYP3A4 inhibitors. Alternative corticosteroids that are less affected by CYP3A4 inhibitors should be considered, like beclomethasone, prednisone, and prednisolone. If concurrent therapy is warranted, patients should be closely monitored for systemic effects. The corticosteroid may need to be discontinued.

DISCUSSION: In a study, boceprevir (800 mg TID for 7 days) increased the area-under-curve (AUC) of a single dose of prednisone (40 mg) by 22%. The maximum concentration (Cmax) and AUC of prednisolone increased by 16% and 37%, respectively.(3) A study of 14 healthy adults found that concurrent use of ketoconazole with ciclesonide increased the AUC of ciclesonide's active metabolite, des-ciclesonide, by approximately 3.6-fold at steady state, while levels of ciclesonide remained unchanged. However, the study concluded that no dosage adjustments were required because ciclesonide has a very low potential to cause side effects.(4) A study in 18 healthy subjects examined the effects of ritonavir (100 mg twice daily) on fluticasone nasal spray (200 mcg daily). In most subjects, fluticasone was undetectable (<10 pg/ml) when administered alone. In subjects in whom fluticasone was detectable when given alone, Cmax and area-under-curve AUC averaged 11.9 pg/ml and 8.43 pg x hr/ml, respectively. With concurrent ritonavir, fluticasone Cmax and AUC increased to 318 pg/ml and 3102.6 pg x hr/ml, respectively.(6-8) This reflects increases in Cmax and AUC by 25-fold and 350-fold, respectively.(6) The cortisol AUC decreased by 86%.(10-13) In a study in 10 healthy subjects, ritonavir (200 mg twice daily for 4 and 14 days) increased the AUC of a single dose of prednisolone by 1.41-fold and 1.30-fold, respectively, after 4 days and 14 days of ritonavir.(14) There have been several case reports of Cushing's syndrome in patients treated concurrently with ritonavir and inhaled budesonide,(15-16) dexamethasone,(17) injectable triamcinolone,(18-21) nasal fluticasone.(23-41) Hepatitis has also been reported with concurrent budesonide and ritonavir.(42) In a study in 9 healthy subjects, mibefradil (50 mg once daily for 3 days) increased the AUC, Cmax, and elimination half-life of methylprednisolone by 3.8-fold, 1.8-fold, and 2.7-fold, respectively.(43) In a study in 8 healthy subjects, following nefazodone administration the following changes were seen with methylprednisolone: mean (+/-SD) area under the concentration-time curve was significantly higher (1393 +/- 343 vs. 2966 +/- 928 ug*h/L; P < 0.005), apparent clearance was lower (28.7 +/- 7.2 vs. 14.6 +/- 7.8 L/h; P < 0.02) and the terminal elimination half-life was longer (2.28 +/- 0.49 vs. 3.32 +/- 0.95 hours; P < 0.02).(44) Selected steroids metabolized by CYP3A4 are linked to this monograph.(45) Selected CYP3A4 inhibitors linked to this monograph include: adagrasib, boceprevir, ceritinib, clarithromycin, erythromycin, itraconazole, josamycin, ketoconazole, lonafarnib, mibefradil, nefazodone, paritaprevir, posaconazole, ribociclib, telaprevir, telithromycin, troleandomycin, tucatinib, and voriconazole.(1-2,45)

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

Anticholinergics/Topiramate

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

MECHANISM OF ACTION: Topiramate can cause decreased sweating and elevated body temperature. Agents with anticholinergic activity can predispose patients to heat-related disorders.(1-2)

CLINICAL EFFECTS: Concurrent use of topiramate with agents with anticholinergic activity may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death.

PREDISPOSING FACTORS: Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1)

PATIENT MANAGEMENT: The manufacturer of topiramate states that caution should be used when topiramate is prescribed with other medicinal products that predispose to heat-related disorders, such as agents with anticholinergic activity (e.g. clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine, and oxybutynin) concurrently with zonisamide.(1) Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of dehydration, oligohidrosis, or elevated body temperature occur, discontinuation of zonisamide should be considered.

DISCUSSION: Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment.(1) A 64-year old woman developed non-exertional hyperthemia while taking multiple psychiatric medications with topiramate.(2)

Anticholinergics/Zonisamide

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

MECHANISM OF ACTION: Zonisamide can cause decreased sweating and elevated body temperature. Agents with anticholinergic activity can predispose patients to heat-related disorders.(1-2)

CLINICAL EFFECTS: Concurrent use of zonisamide with agents with anticholinergic activity may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death.

PREDISPOSING FACTORS: Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1)

PATIENT MANAGEMENT: The UK and US manufacturers of zonisamide state that caution should be used in adults when zonisamide is prescribed with other medicinal products that predispose to heat-related disorders, such as agents with anticholinergic activity.(1-2) Pediatric and adolescent patients must not take anticholinergic agents (e.g. clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine, and oxybutynin) concurrently with zonisamide.(1) Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of dehydration, oligohidrosis, or elevated body temperature occur, discontinuation of zonisamide should be considered.

DISCUSSION: Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment and resulted in death.(1)

Selected Corticosteroids/Levoketoconazole

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

MECHANISM OF ACTION: Levoketoconazole may inhibit the CYP3A4 mediated metabolism of some corticosteroids, resulting in increased systemic exposure. Levoketoconazole may also suppress endogenous cortisol output. Levoketoconazole is the enantiomer of ketoconazole.

CLINICAL EFFECTS: Concurrent use of levoketoconazole may result in elevated levels of and effects from the corticosteroid, including Cushing syndrome. These effects have been seen with systemic as well as inhaled corticosteroids.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients should be carefully monitored with concurrent administration of these agents, or when levoketoconazole is added to corticosteroid therapy. The dose of the corticosteroid may need to be adjusted or alternative therapy considered.

DISCUSSION: The concurrent use of ketoconazole has been shown to increase budesonide area-under-curve (AUC) by eight-fold. In a study in eight healthy subjects, the simultaneous administration of ketoconazole increased budesonide AUC by 6.5-fold. Administering the two agents 12 hours apart increased budesonide AUC by 3.8-fold. In a study in 6 healthy subjects, pretreatment with ketoconazole (200 mg daily) increased the AUC of a single intravenous dose of methylprednisolone (20 mg) by 135% and decreased its clearance by 60%. Concurrent ketoconazole also increased the reduction in 24-hour cortisol AUC and suppressed morning cortisol concentrations. In a study in 8 healthy subjects, ketoconazole decreased the clearance of methylprednisolone by 46% and increased mean residence time by 37%. In a randomized, cross-over study in 6 healthy subjects, pretreatment with ketoconazole (200 mg daily for 6 days) had no effect on the pharmacokinetics of a single intravenous dose of prednisolone (14.8 mg). In a study, concurrent oral ketoconazole increased the AUC of des-ciclesonide from orally inhaled ciclesonide by 3.6-fold. There were no changes in ciclesonide levels. In a study in 24 healthy subjects, subjects were randomized to receive either ketoconazole (200 mg BID) or placebo on Days 4-9 of a a 9 day course of mometasone (400 mcg BID). No subject had mometasone levels greater than 150 pcg/ml on Day 3. Four of 12 subjects who received ketoconazole had mometasone Cmax levels greater than 200 mcg/ml on Day 9. Plasma cortisol levels appeared to decrease as well. In a cross-over study in 15 healthy subjects, subjects were randomized to receive fluticasone furoate and vilanterol on days 5-11 with either ketoconazole (200mg once daily) or placebo for days 1-11 with a washout period of 7-14 days. Fluticasone furoate AUC was increased by 36%, Cmax was increased by 33%, and decreased systemic cortisol levels by 27%. There were no effects on heart rate and blood potassium levels. There was a small increase in QTc which was 7.6ms greater when compared to placebo; however, ketoconazole has been reported to increase QTc by 5-6ms. Vilanterol AUC was increased by 65% and Cmax was increased by 22%. There were no effects on heart rate and blood potassium levels. No serious adverse events occurred and no subjects withdrew from the study due to adverse events. The most common adverse event reported was headache. Coadministration of orally inhaled fluticasone (1000 mcg) and ketoconazole (200 mg once daily) resulted in a 1.9-fold increase in plasma fluticasone exposure and a 45% decrease in plasma cortisol AUC.

Selected Cyp2d6 Inhibitors/Metoprolol

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

MECHANISM OF ACTION: CYP2D6 inhibitors may inhibit the metabolism of metoprolol.(1,2)

CLINICAL EFFECTS: Concurrent use of CYP2D6 inhibitors may result in elevated levels of and toxicity from metoprolol.(1,2)

PREDISPOSING FACTORS: The interaction may be more severe in patients who are ultrarapid metabolizers of CYP2D6,(1,2) elderly,(3) and on higher doses of beta-blockers.(3)

PATIENT MANAGEMENT: Monitor patients receiving concurrent therapy with metoprolol and inhibitors of CYP2D6. The dosage of metoprolol may need to be adjusted.(1,2) The effects of rolapitant, a moderate CYP2D6 inhibitor, on CYP2D6 are expected to last at least 28 days after administration.(4)

DISCUSSION: In a case report, a patient maintained on metoprolol developed bradycardia following the addition of bupropion.(5) In a study in 20 healthy females, diphenhydramine increased the AUC of metoprolol by 21%. Heart rate reduction increased 29%.(6) In a randomized study in 16 healthy subjects, diphenhydramine decreased metoprolol oral and nonrenal clearance by 2-fold in extensive 2D6 metabolizers. In extensive 2D6 metabolizers, metoprolol-induced effects on heart rate, systolic blood pressure, and aortic blood flow peak velocity were all increased. There were no effects of diphenhydramine in poor metabolizers.(7) Fluoxetine has been shown to inhibit metoprolol metabolism in vitro.(8) There is a case report of severe bradycardia following the addition of fluoxetine to metoprolol.(9) In a 3-way, randomized, cross-over study in healthy subjects, paroxetine (20 mg daily) increased the area-under-curve (AUC) of both S- and R-metoprolol by 3-fold, and 4-fold, respectively, regardless of whether the formulation of metoprolol was immediate release or extended release. Concurrent paroxetine also significantly decreased heart rate and blood pressure when compared to metoprolol alone.(10) In an open-label, randomized, cross-over study in 10 healthy subjects, paroxetine increased the AUC of S-metoprolol and R-metoprolol from an immediate release formulation (50 mg)by 4-fold and 5-fold, respectively. Paroxetine increased the AUC of S-metoprolol and R-metoprolol from an extended release formulation (100 mg) by 3-fold and 4-fold, respectively.(11) In a study in patients with acute myocardial infarction and depression, paroxetine (20 mg daily) increased the AUC of metoprolol 3-fold. Mean heart rate was significantly lower following the addition of paroxetine to metoprolol. Two patients experienced bradycardia and severe orthostatic hypotension.(12) In an open trial in 8 healthy males, paroxetine (20 mg daily) increased the AUC of S-metoprolol and R-metoprolol by 4-fold and 7-fold, respectively.(13) There are case reports of complete atrioventricular block(14) and bradycardia(15) with concurrent metoprolol and paroxetine. A systematic review and meta-analysis of CYP2D6 interactions between metoprolol and either paroxetine or fluoxetine reviewed 9 articles including 4 primary and 2 observational studies as well as 3 case reports. Experimental studies noted paroxetine increased the AUC of metoprolol 3-fold to 5-fold and significantly decreased blood pressure and heart rate. Paroxetine and fluoxetine have shown equipotent inhibitor capacity on CYP2D6. The metabolite, norfluoxetine, is also an inhibitor of CYP2D6.(16) A retrospective cohort study evaluated morbidity in patients on a beta-blocker primarily metabolized by CYP2D6 (e.g., nebivolol, metoprolol, carvedilol, propranolol, labetalol) and started on a strong or moderate CYP2D6-inhibiting antidepressant (e.g., fluoxetine, paroxetine, bupropion, duloxetine). Use of such an antidepressant with a beta-blocker was associated with an increased risk of hospitalization or ED visit due to an adverse hemodynamic event (HR 1.53, 95% CI 1.03-2.81, p=0.04).(3) CYP2D6 inhibitors include: abiraterone, bupropion, celecoxib, cinacalcet, citalopram, dacomitinib, dimenhydrinate, diphenhydramine, duloxetine, escitalopram, fedratinib, fluoxetine, hydroxychloroquine, imatinib, lorcaserin, osilodrostat, paroxetine, ranitidine, ranolazine, rolapitant, and sertraline. One or more of the drug pairs linked to this monograph have been included in a list of interactions that could be considered for classification as "non-interruptive" in EHR systems. This DDI subset was vetted by an expert panel commissioned by the U.S. Office of the National Coordinator (ONC) for Health Information Technology.

Selected Cyp2d6 Inhibitors/Propranolol

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

MECHANISM OF ACTION: CYP2D6 inhibitors may inhibit the metabolism of propranolol.(1)

CLINICAL EFFECTS: Concurrent use of CYP2D6 inhibitors may result in elevated levels of and toxicity from propranolol, including hypotension and bradycardia.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Monitor patients receiving concurrent therapy with propranolol and CYP2D6 inhibitors. The dosage of propranolol may need to be adjusted.(1)

DISCUSSION: In a pharmacokinetic study in 16 healthy volunteers, concurrent use of quinidine 200 mg (a CYP2D6 inhibitor) increased the area-under-curve (AUC) of propranolol by 2.29-fold.(2) In a pharmacokinetic study in 6 healthy subjects, concurrent use of quinidine increased propranolol AUC 2-fold.(3) A retrospective review of concurrent use of propranolol and antidepressants evaluated the risk of hospitalization or emergency room visit within 30 days of concurrent prescription. In patients receiving antidepressants with moderate to strong CYP2D6 inhibitory effects, patient were an increased risk compared to patients receiving no antidepressants (Hazard Ratio (HR) = 1.53; 95% CI 1.03-2.81 vs. HR = 1.24; 95% CI 0.82-1.88).(4) Case reports of bradycardia and cardiac adverse effects have been reported with concurrent use of propranolol and the antidepressants fluoxetine and paroxetine (strong CYP2D6 inhibitors).(5) Strong CYP2D6 inhibitors include: bupropion, dacomitinib, fluoxetine, mavorixafor, and paroxetine. Moderate CYP2D6 inhibitors include: abiraterone, asunaprevir, berotralstat, capivasertib, cinacalcet, duloxetine, eliglustat, escitalopram, levomepromazine, lorcaserin, mirabegron, moclobemide, quinine, ranolazine, and rolapitant. Weak CYP2D6 inhibitors include: desvenlafaxine, diphenhydramine, dimenhydrinate, dronabinol, fedratinib, hydroxychloroquine, imatinib, osilodrostat, ranitidine, and sertraline.(6)

Selected Steroids/Ensitrelvir; Nirmatrelvir-Ritonavir

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

MECHANISM OF ACTION: Ensitrelvir and nirmatrelvir/ritonavir may inhibit the metabolism of corticosteroids metabolized by CYP3A4.(1,2)

CLINICAL EFFECTS: Ensitrelvir and nirmatrelvir/ritonavir may result in increased systemic exposure to and effects from corticosteroids metabolized by CYP3A4.(1,2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Coadministration with corticosteroids of all routes of administration of which exposures are significantly increased by strong CYP3A4 inhibitors can increase the risk of Cushing's syndrome and adrenal suppression. However, the risk of Cushing's syndrome and adrenal suppression associated with short-term use of a strong CYP3A4 inhibitor is low.(1) The manufacturer of nirmatrelvir/ritonavir recommends considering alternative corticosteroids including beclomethasone, prednisone, and prednisolone.(1)

DISCUSSION: Concurrent use of a single dose of midazolam 2 mg, a CYP3A4 substrate, with nirmatrelvir-ritonavir (300 mg/100 mg twice daily for nine doses) increased the maximum concentration (Cmax) and area-under-curve (AUC) of midazolam by 37% and 143%, respectively.(1) A study in 18 healthy subjects examined the effects of ritonavir (100 mg twice daily) on fluticasone nasal spray (200 mcg daily). In most subjects, fluticasone was undetectable (<10 pg/ml) when administered alone. In subjects in whom fluticasone was detectable when given alone, Cmax and area-under-curve AUC averaged 11.9 pg/ml and 8.43 pg x hr/ml, respectively. With concurrent ritonavir, fluticasone Cmax and AUC increased to 318 pg/ml and 3102.6 pg x hr/ml, respectively.(7,11,13) This reflects increases in Cmax and AUC by 25-fold and 350-fold, respectively.(3) The cortisol AUC decreased by 86%.(4-7) In a study in 10 healthy subjects, ritonavir (200 mg twice daily for 4 and 14 days) increased the AUC of a single dose of prednisolone by 1.41-fold and 1.30-fold, respectively, after 4 days and 14 days of ritonavir.(8) In a clinical study, ensitrelvir (750 mg on day 1 and 250 mg on days 2-5) increased the Cmax and AUC of dexamethasone 1 mg single dose by 1.47-fold and 3.47-fold, respectively.(2) Selected steroids linked to this monograph include: budesonide, ciclesonide, dexamethasone, fluticasone, methylprednisolone, and triamcinolone.(9)

Selected Weak Cyp2d6 Inhibitors/Tamoxifen

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

MECHANISM OF ACTION: Inhibitors of CYP2D6 may inhibit the conversion of tamoxifen to endoxifen (an active metabolite of tamoxifen).(1-2) The role of endoxifen in tamoxifen's efficacy has been debated and may involve a minimum concentration level.(3-5)

CLINICAL EFFECTS: Concurrent use of inhibitors of CYP2D6 may decrease the effectiveness of tamoxifen in preventing breast cancer recurrence.

PREDISPOSING FACTORS: Concurrent use of weak CYP2D6 inhibitors in patients who are CYP2D6 intermediate metabolizers should be avoided. Patients who are CYP2D6 poor metabolizers lack CYP2D6 function and are not affected by CYP2D6 inhibition.

PATIENT MANAGEMENT: Although data on this interaction are conflicting, it may be prudent to use alternatives to CYP2D6 inhibitors when possible in patients taking tamoxifen. The US manufacturer of tamoxifen states that the impact on the efficacy of tamoxifen by strong CYP2D6 inhibitors is uncertain and makes no recommendation regarding coadministration with inhibitors of CYP2D6.(12) The manufacturer of paroxetine (a strong CYP2D6 inhibitor) states that alternative agents with little or no CYP2D6 inhibition should be considered.(13) The National Comprehensive Cancer Network's breast cancer guidelines advises caution when coadministering strong CYP2D6 inhibitors with tamoxifen.(14) NCCN states when prescribing a selective serotonin reuptake inhibitor (SSRI), it is reasonable to avoid SSRIs that are strong and moderate CYP2D6 inhibitors, particularly fluoxetine and paroxetine, if an appropriate alternative exists.(14) Cancer Care Ontario breast cancer guidelines state concurrent use of weak CYP2D6 inhibitors should be closely monitored.(15) The European Society of Medical Oncology (ESMO) clinical practice guidelines for early breast cancer states patients on tamoxifen should be advised to avoid concurrent use of strong and moderate CYP2D6 inhibitors. Consider alternatives to tamoxifen if CYP2D6 inhibitors cannot be replaced with alternative agents.(16) If concurrent therapy is warranted, the risks versus benefits should be discussed with the patient.

DISCUSSION: Some studies have suggested that administration of fluoxetine, paroxetine, and quinidine with tamoxifen or a CYP2D6 poor metabolizer phenotype may result in a decrease in the formation of endoxifen (an active metabolite of tamoxifen) and a shorter time to breast cancer recurrence.(1-2,9) A retrospective study of 630 breast cancer patients found an increasing risk of breast cancer mortality with increasing durations of coadministration of tamoxifen and paroxetine. In the adjusted analysis, absolute increases of 25%, 50%, and 75% in the proportion of time of overlapping use of tamoxifen with paroxetine was associated with 24%, 54%, and 91% increase in the risk of death from breast cancer, respectively.(18) The CYP2D6 genotype of the patient may have a role in the effects of this interaction. Patients with wild-type CYP2D6 genotype may be affected to a greater extent by this interaction. Patients with a variant CYP2D6 genotype may have lower baseline levels of endoxifen and may be affected to a lesser extent by this interaction.(6-10) In a retrospective review, 1,325 patients treated with tamoxifen for breast cancer were classified as being poor 2D6 metabolizers (lacking functional CYP2D6 enzymes), intermediate metabolizers (heterozygous alleles), or extensive metabolizers (possessing 2 functional alleles). After a mean follow-up period of 6.3 years, the recurrence rates were 14.9%, 20.9%, and 29.0%, in extensive metabolizers, intermediate metabolizers, and poor metabolizers, respectively.(11) In October of 2006, the Advisory Committee Pharmaceutical Science, Clinical Pharmacology Subcommittee of the US Food and Drug Administration recommended that the US tamoxifen labeling be updated to include information about the increased risk of breast cancer recurrence in poor CYP2D6 metabolizers (either by genotype or drug interaction).(19-20) The labeling changes were never made due to ongoing uncertainty about the effects of CYP2D6 genotypes on tamoxifen efficacy. In contrast to the above information, two studies have shown no relationship between CYP2D6 genotype and breast cancer outcome.(21-23) As well, a number of studies found no association between use of CYP2D6 inhibitors and/or antidepressants in patients on tamoxifen and breast cancer recurrence,(24-28) though the studies were limited by problematic selection of CYP2D6 inhibitors and short follow-up. Weak inhibitors of CYP2D6 include: alogliptin, artesunate, celecoxib, chloroquine, cimetidine, clobazam, clomipramine, cobicistat, delavirdine, diltiazem, dimenhydrinate, diphenhydramine, dronabinol, dupilumab, echinacea, enasidenib, fedratinib, felodipine, fluvoxamine, gefitinib, hydralazine, imatinib, labetalol, lorcaserin, nicardipine, osilodrostat, ranitidine, ritonavir, sarpogrelate, sertraline, verapamil and viloxazine.(29)

Weak Cyp2d6 Inhibitors/Eliglustat

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

MECHANISM OF ACTION: Weak inhibitors of CYP2D6 may inhibit the metabolism of eliglustat. If the patient is also taking an inhibitor of CYP3A4, eliglustat metabolism can be further inhibited.(1)

CLINICAL EFFECTS: Concurrent use of an agent that is a weak inhibitor of CYP2D6 may result in elevated levels of and clinical effects of eliglustat, including prolongation of the PR, QTc, and/or QRS intervals, which may result in life-threatening cardiac arrhythmias.(1)

PREDISPOSING FACTORS: If the patient is also taking an inhibitor of CYP3A4 and/or has hepatic impairment, eliglustat metabolism can be further inhibited.(1) The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(2) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(2)

PATIENT MANAGEMENT: The dosage of eliglustat with weak inhibitors of CYP2D6 in poor CYP2D6 metabolizers should be limited to 84 mg daily.(1) The dosage of eliglustat with weak inhibitors of CYP2D6 in extensive CYP2D6 metabolizers with mild (Child-Pugh Class A) hepatic impairment should be limited to 84 mg daily.(1) If concurrent therapy is warranted, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting.

DISCUSSION: Paroxetine (30 mg daily), a strong inhibitor of CYP2D6, increased eliglustat (84 mg BID) maximum concentration (Cmax) and area-under-curve (AUC) by 7-fold and 8.4-fold, respectively, in extensive metabolizers. Physiologically-based pharmacokinetic (PKPB) models suggested paroxetine would increase eliglustat Cmax and AUC by 2.1-fold and 2.3-fold, respectively, in intermediate metabolizers. PKPB models suggested ketoconazole may increase the Cmax and AUC of eliglustat (84 mg daily) by 4.3-fold and 6.2-fold, respectively, in poor metabolizers.(1) PKPB models suggested terbinafine, a moderate inhibitor of CYP2D6, would increase eliglustat Cmax and AUC by 3.8-fold and 4.5-fold, respectively, in extensive metabolizers and by 1.6-fold and 1.6-fold, respectively in intermediate metabolizers. PKPB models suggest that concurrent eliglustat (84 mg BID), paroxetine (a strong inhibitor of CYP2D6), and ketoconazole would increase eliglustat Cmax and AUC by 16.7-fold and 24.2-fold, respectively, in extensive metabolizers. In intermediate metabolizers, eliglustat Cmax and AUC would be expected to increase 7.5-fold and 9.8-fold, respectively.(1) PKPB models suggest that concurrent eliglustat (84 mg BID), terbinafine (a moderate inhibitor of CYP2D6), and ketoconazole would increase eliglustat Cmax and AUC by 10.2-fold and 13.6-fold, respectively, in extensive metabolizers. In intermediate metabolizers, eliglustat Cmax and AUC would be expected to increase 4.2-fold and 5-fold, respectively.(1) A single dose of rolapitant increased dextromethorphan, a CYP2D6 substrate, about 3-fold on days 8 and day 22 following administration. Dextromethorphan levels remained elevated by 2.3-fold on day 28 after single dose rolapitant. The inhibitory effects of rolapitant on CYP2D6 are expected to persist beyond 28 days.(5) Weak inhibitors of CYP2D6 include: alogliptin, artesunate, celecoxib, chloroquine, chlorpromazine, clobazam, clomipramine, desvenlafaxine, dimenhydrinate, diphenhydramine, dronabinol, dupilumab, echinacea, enasidenib, felodipine, gefitinib, hydralazine, hydroxychloroquine, lorcaserin, methadone, panobinostat, propafenone, sarpogrelate, sertraline, vemurafenib, and venlafaxine.(3,4)

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There are no contraindication contraindications for this drug.

• Angle-closure glaucoma
• Benign prostatic hyperplasia
• Bladder outflow obstruction
• Chronic idiopathic constipation
• Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
• Chronic kidney disease stage 5 (failure) GFr<15 ml/min
• Disease of liver
• Gastrointestinal obstruction
• Nasal septal perforation
• Nasal septal ulcers
• Nasal trauma
• Ocular herpes simplex
• Ocular hypertension
• Open angle glaucoma
• Operation on nose
• Severe infection
• Stenosing peptic ulcer
• Urinary retention

• Adrenocortical insufficiency
• Cataracts
• Chronic obstructive pulmonary disease
• Coronary artery disease
• Epistaxis
• Hypertension
• Hyperthyroidism
• Inactive tuberculosis
• Kidney disease with reduction in glomerular filtration rate (GFr)
• Ocular hypertension
• Parasitic infection
• Pyloroduodenal obstruction
• Seizure disorder

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Less Frequent

• Bronchitis
• Lesion of nasal mucosa
• Urticaria

Rare or Very Rare

• Abnormal hepatic function tests
• Acute bacterial otitis media
• Acute generalized exanthematous pustulosis
• Adrenocortical insufficiency
• Anaphylaxis
• Anaphylaxis
• Anaphylaxis
• Anaphylaxis
• Angioedema
• Blood dyscrasias
• Bronchospastic pulmonary disease
• Cardiac arrhythmia
• Cataracts
• Cholestasis
• Contact dermatitis
• Dehydration
• Edema
• Extrasystoles
• Glaucoma
• Glomerulonephritis
• Hallucinations
• Hearing loss
• Hemolytic anemia
• Hemolytic anemia
• Hepatitis
• Hypercortisolism
• Hypersensitivity drug reaction
• Hypersensitivity drug reaction
• Hypotension
• Immunosuppression
• Impaired wound healing
• Nasal candidiasis
• Nasal septal perforation
• Palpitations
• Pharyngeal candidiasis
• Seizure disorder
• Seizure disorder
• Skin rash
• Thrombocytopenic disorder
• Tongue swelling
• Tonic clonic seizure
• Upper respiratory infection
• Urticaria

More Frequent

• Anticholinergic toxicity
• Dizziness
• Drowsy
• Drowsy
• Dry nose
• Dry nose
• Dry throat
• Epistaxis
• Headache disorder
• Nasal passage irritation
• Pharyngitis
• Thick bronchial secretions
• Xerostomia

Less Frequent

• Acute abdominal pain
• Acute abdominal pain
• Back pain
• Cough
• Crusted nasal mucosa
• Diarrhea
• Dizziness
• Dizziness
• Drowsy
• Dysgeusia
• Dysmenorrhea
• Dyspepsia
• Epistaxis
• Erythema of nasal mucosa
• Fatigue
• Fatigue
• Fever
• Headache disorder
• Insomnia
• Muscle weakness
• Myalgia
• Nasal congestion
• Nasal pain
• Nausea
• Nausea
• Pain in oropharynx
• Pharyngitis
• Pharyngitis
• Rhinorrhea
• Sedation
• Sinusitis
• Sinusitis
• Skin rash
• Sore throat
• Viral infection
• Vomiting
• Xerostomia
• Xerostomia

Rare or Very Rare

• Abdominal distension
• Abdominal pain with cramps
• Accidental fall
• Acne vulgaris
• Acute abdominal pain
• Acute cognitive impairment
• Acute cognitive impairment
• Aggressive behavior
• Agitation
• Agitation
• Alopecia
• Anorexia
• Anorexia
• Anticholinergic toxicity
• Ataxia
• Blurred vision
• Blurred vision
• Blurred vision
• Chest discomfort
• Chills
• Constipation
• Constipation
• Cough
• Cramps in legs
• Diarrhea
• Diplopia
• Dizziness
• Dry nose
• Dry throat
• Dysgeusia
• Dyskinesia
• Dyspepsia
• Dyspnea
• Dysuria
• Dysuria
• Earache
• Eructation
• Euphoria
• Euphoria
• Excitement
• Excitement
• Fatigue
• Fever
• Flatulence
• Flu-like symptoms
• Gastritis
• Hallucinations
• Headache disorder
• Headache disorder
• Hemorrhoids
• Hyperhidrosis
• Hyperhidrosis
• Increased appetite
• Insomnia
• Insomnia
• Irritability
• Maculopapular rash
• Malaise
• Memory impairment
• Migraine
• Nausea
• Nervousness
• Nervousness
• Nervousness
• Nightmares
• Nightmares
• Nightmares
• Pain
• Palpitations
• Paresthesia
• Parosmia
• Pruritus of skin
• Pruritus of skin
• Pruritus of skin
• Skin photosensitivity
• Skin photosensitivity
• Skin rash
• Skin rash
• Stomatitis
• Symptoms of anxiety
• Syncope
• Tachycardia
• Tachycardia
• Tinnitus
• Tinnitus
• Tongue discoloration
• Toothache
• Tremor
• Tremor
• Unsteady gait
• Urinary retention
• Urinary retention
• Urticaria
• Vertigo
• Visual changes
• Visual changes
• Voice change
• Vomiting
• Vomiting
• Weight gain
• Wheezing
• Xerostomia

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Reproduction studies in mice, rats, and rabbits using oral cetirizine hydrochloride dosages up to 96, 225, and 135 mg/kg daily, respectively (approximately 40, 180, and 220 times, respectively, the maximum recommended daily oral dosage in adults on a mg/m2 basis), have not revealed evidence of teratogenicity. Because there are no adequate and controlled studies to date using cetirizine in pregnant women and animal studies are not always predictive of human response, cetirizine hydrochloride should be used during pregnancy only when clearly needed.

Cetirizine hydrochloride in combination with pseudoephedrine has been shown to increase the number of fetal skeletal malformations (rib distortions) and variants (unossified sternebrae) in rats when given orally in a fixed-combination ratio at a dosage of 6/154 mg/kg (approximately 5 times the maximum recommended adult dosage on a mg/m2 basis). These effects were not observed at a dosage of 1.6/38 mg/kg (approximately the maximum recommended adult dosage on a mg/m2 basis). Reproduction studies in rabbits using cetirizine hydrochloride and pseudoephedrine hydrochloride in a fixed-combination ratio at a dosage of up to 6/154 mg/kg (approximately 10 times the maximum recommended adult dosage on a mg/m2 basis) have not revealed evidence of harm to the fetus. There are no adequate and controlled studies to date using cetirizine hydrochloride and pseudoephedrine hydrochloride in pregnant women, and the fixed combination should be used during pregnancy only when the potential benefits justify the possible risks to the fetus.

In lactating beagles, about 3% of a cetirizine dose was distributed in milk. In mice, cetirizine caused retarded pup weight gain during lactation when dams were receiving a cetirizine hydrochloride dosage of 96 mg/kg daily (about 40 times the maximum recommended daily dosage in adults on a mg/m2 basis). In rats, cetirizine hydrochloride and pseudoephedrine hydrochloride caused retarded pup weight gain and decreased viability during lactation when administered orally to dams in fixed combination at a dosage of 6/154 mg/kg (approximately 5 times the maximum recommended adult dosage on a mg/m2 basis) but not when administered at a dosage of 1.6/38 mg/kg (approximately the maximum recommended adult dosage on a mg/m2 basis). Cetirizine is distributed into human milk. Pseudoephedrine also distributes into human milk. Therefore, use of cetirizine hydrochloride alone or in combination with pseudoephedrine hydrochloride in nursing women is not recommended.

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