Cafergot (ergotamine tartrate/caffeine)

Some clinicians suggest that when used as a mild CNS stimulant to overcome fatigue, oral doses of 100-200 mg of anhydrous caffeine are required. The manufacturers state that adults and children 12 years of age or older may receive a dosage of 100-200 mg no more frequently than every 3-4 hours.

For the treatment of apnea of prematurity, commercially available caffeine citrate injection in a loading dose of 20 mg/kg (10 mg/kg when expressed in terms of anhydrous caffeine) is administered by slow IV infusion (i.e., over 30 minutes) using a syringe infusion pump. Beginning 24 hours after the loading dose, maintenance doses of caffeine citrate of 5 mg/kg (2.5 mg/kg when expressed as anhydrous caffeine) may be administered every 24 hours, either orally or via slow IV infusion (i.e., over 10 minutes) using a syringe infusion pump. The manufacturer states that the safety and efficacy of dosing periods exceeding 10-12 days have not been established. Other dosing regimens+ for the treatment of apnea of prematurity have used caffeine doses (in terms of anhydrous caffeine) of 5-10 mg/kg, given IV, IM, or orally as a loading dose, and followed by 2.5-5 mg/kg, given IV, IM, or orally once daily. Maintenance dosage has been adjusted according to the patient's response and tolerance and plasma caffeine concentrations.

When caffeine citrate is used for the treatment of apnea of prematurity in infants with hepatic or renal impairment, serum concentrations of caffeine should be monitored and dosage adjusted to avoid toxicity.

Analeptic use of caffeine is strongly discouraged by most clinicians. However, the manufacturers of caffeine and sodium benzoate injection recommend IM, or in emergency respiratory failure, IV injection of 500 mg of the drug (about 250 mg of anhydrous caffeine) or a maximum single dose of 1 g (about 500 mg of anhydrous caffeine) for the treatment of respiratory depression associated with overdosage of CNS depressants, including opiate analgesics and alcohol, and with electric shock.

Some clinicians recommend that when caffeine and sodium benzoate injection is used in children for CNS stimulation+, an IM, IV, or subcutaneous dose of 8 mg/kg (about 4 mg of anhydrous caffeine per kg) (not to exceed 500 mg) or 250 mg/m2 (about 125 mg of anhydrous caffeine per m2) be given up to every 4 hours if necessary.

Ergotamine tartrate is given sublingually. A combination of ergotamine tartrate and caffeine may be administered orally, or rectally as a suppository. If the suppositories become softened, they should be chilled in ice-cold water to solidify before removing the foil wrapper.

To be most effective, ergotamine tartrate should be administered as soon as possible after the first symptoms of a vascular headache (i.e., during the prodromal phase if there is one or at the beginning of an attack). The amount of drug required and the speed and degree of relief are thought to be directly related to the promptness with which the drug is started. After the initial dose is administered, the patient should lie down and relax in a quiet, darkened room. Ergotamine should not be administered within 24 hours of a selective serotonin agonist (e.g., sumatriptan). (See Drug Interactions: Selective Serotonin Agonists.)

Caffeine may be administered orally. Caffeine citrate is administered orally or by slow IV infusion using a syringe infusion pump. Caffeine and sodium benzoate injection may be administered by IM or slow IV injection; the drug has also been administered subcutaneously.

The preservative-free commercially available injection is for single use only, and any unused portion should be discarded. It is important that such oral solution be measured accurately (e.g., using a 1-mL or other appropriate syringe).

There is no enhanced messaging for this drug.

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

Cyp1a2 Inhibitors/Fezolinetant

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: Inhibitors of CYP1A2 may inhibit the metabolism of fezolinetant.(1-4)

CLINICAL EFFECTS: Concurrent use of a CYP1A2 inhibitor may increase levels of and adverse effects from fezolinetant.(1-4)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Recommendations for concurrent use of fezolinetant with CYP1A2 inhibitors differ in different regions. The US manufacturer of fezolinetant states that concurrent use with strong, moderate, and weak CYP1A2 inhibitors is contraindicated.(1) The Australian, Canadian, and UK manufacturers of fezolinetant state that concurrent use with strong and moderate CYP1A2 inhibitors is contraindicated, while weak CYP1A2 inhibitors are not predicted to cause clinically relevant changes in fezolinetant exposure.(2-4)

DISCUSSION: In a study, fluvoxamine, a strong CYP1A2 inhibitor, increased fezolinetant maximum concentration (Cmax) and area-under-curve (AUC) by 80% and 840%, respectively. Mexiletine (400 mg every 8 hours), a moderate CYP1A2 inhibitor, increased fezolinetant Cmax and AUC by 40% and 360%, respectively. Cimetidine (300 mg every 6 hours), a weak CYP1A2 inhibitor, increased fezolinetant Cmax and AUC by 30% and 100%, respectively.(1) Strong CYP1A2 inhibitors linked to this monograph include angelica root, ciprofloxacin, enasidenib, enoxacin, fluvoxamine, and rofecoxib. Moderate CYP1A2 inhibitors linked to this monograph include capmatinib, centanafadine, dipyrone, fexinidazole, genistein, hormonal contraceptives, methoxsalen, mexiletine, osilodrostat, phenylpropanolamine, pipemidic acid, rucaparib, troleandomycin, vemurafenib, and viloxazine. Weak CYP1A2 inhibitors linked to this monograph include acyclovir, allopurinol, artemisinin, belumosudil, caffeine, cannabidiol, cimetidine, curcumin, dan-shen, deferasirox, disulfiram, Echinacea, famotidine, ginseng, norfloxacin, obeticholic acid, parsley, piperine, propafenone, propranolol, ribociclib, simeprevir, thiabendazole, ticlopidine, triclabendazole, valacyclovir, verapamil, and zileuton.(5-7)

Ergot Alkaloids/5-Ht1d Agonists

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: The 5-HT1D agonists and ergot alkaloids can produce vasospastic reactions.

CLINICAL EFFECTS: Concurrent therapy may produce additive vasospastic effects.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturer states that sumatriptan should not be used within 24 hours of an ergotamine-containing or ergotamine-like medication (such as dihydroergotamine or methysergide).(1,2) The Australian(3) and UK(4,5) manufacturers state that 24 hours should elapse before sumatriptan is administered following an ergotamine-containing preparation and 6 hours should elapse before an ergotamine-containing preparation is administered following sumatriptan. The US manufacturer states that zolmitriptan should not be used within 24 hours of an ergotamine-containing or ergotamine-like medication.(6) The UK manufacturer states that zolmitriptan should not be used within 6 hours of an ergotamine-containing or ergotamine-like medication.(7) The The Australian manufacturer states that 24 hours should elapse before zolmitriptan is administered following an ergotamine-containing preparation and 6 hours should elapse before an ergotamine-containing medication is administered following zolmitriptan.(8) The US manufacturer states that the use of rizatriptan within 24 hours of an ergotamine-containing or ergot-type medication is contraindicated.(9) The US manufacturer states that the use of naratriptan within 24 hours of an ergotamine-containing or ergot-type medication is contraindicated.(10) The Australian manufacturer states that concurrent use of naratriptan and ergotamine or ergotamine derivatives is not recommended.(11) The US manufacturer states that the use of eletriptan within 24 hours of an ergotamine-containing or ergot-type medication is contraindicated.(12) The UK manufacturer states that the use of eletriptan within 24 hours of an ergotamine-containing or ergot-type medication is not recommended.(13)

DISCUSSION: Because of the theoretical risk of additive vasospastic effects, the US manufacturer states that the use of sumatriptan within 24 hours of an ergotamine-containing or ergotamine-like medication is contraindicated.(1,2) The Australian(3) and UK(4,5) manufacturer states that 24 hours should elapse before sumatriptan is administered following an ergotamine-containing preparation and 6 hours should elapse before an ergotamine-containing medication is administered following sumatriptan. Although the pharmacokinetics of zolmitriptan were not affected by ergotamine, the UK manufacturer of zolmitriptan recommends that 6 hours should elapse between the administration of zolmitriptan and an ergotamine preparation.(7) The US manufacturer of zolmitriptan states under contraindications that zolmitriptan should not be used within 24 hours of an ergotamine-containing or ergot-type medication.(6) The Australian manufacturer states that 24 hours should elapse before zolmitriptan is administered following an ergotamine-containing preparation and 6 hours should elapse before an ergotamine-containing medication is administered following zolmitriptan.(8) Because of the additive risk of prolonged vasospastic reactions, the manufacturers of rizatriptan(9) and naratriptan(10) in the US state that the use of ergotamine-containing or ergot-type medications and these agents is contraindicated. The Australian manufacturer states that concurrent use of naratriptan and ergotamine or ergotamine derivatives is not recommended.(11) Administration of oral ergotamine one and two hours after eletriptan resulted in additive increases in blood pressure.(13)

Ergot Alkaloids/Boceprevir; Telaprevir

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: Boceprevir(1) and telaprevir(2) may inhibit the metabolism of ergot alkaloids by CYP3A4.

CLINICAL EFFECTS: Concurrent use of boceprevir(1) or telaprevir(2) may result in elevated levels of and effects from ergot alkaloids, including peripheral vasospasm and ischemia.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturers of boceprevir(1) and telaprevir(2) state that concurrent use of ergot alkaloids, including dihydroergotamine, ergonovine, ergotamine, and methylergonovine, is contraindicated.

DISCUSSION: Boceprevir has been shown to be a strong inhibitor of CYP3A4.(1) Telaprevir has also been shown to inhibit CYP3A4.(2) Therefore, concurrent use of boceprevir(1) or telaprevir(2) with agents that are highly dependent on CYP3A4 for clearance and for which elevated plasma levels are associated with serious and/or life-threatening events is contraindicated.

Ergot Alkaloids/Delavirdine

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: Delavirdine may inhibit the metabolism of the ergot alkaloids by CYP3A4.(1,2)

CLINICAL EFFECTS: Concurrent administration with delavirdine may result in increased levels, clinical effects, and possible toxicity of the ergot alkaloids.(1,2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of delavirdine states that the concurrent use of ergot alkaloids is contraindicated.(1) The US manufacturer of methylergonovine states that methylergonovine should not be administered with potent CYP3A4 inhibitors such as delavirdine.(2)

DISCUSSION: Delavirdine has been shown to inhibit CYP3A4. Concurrent use of delavirdine with agents that are highly dependent on CYP3A4 for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events, such as the ergot alkaloids, is contraindicated.(1)

Ergot Alkaloids/Itraconazole; Ketoconazole

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: Itraconazole(1,2) and ketoconazole(3-5) may inhibit the metabolism of ergot alkaloids by CYP3A4.

CLINICAL EFFECTS: Concurrent use may result in increased levels of ergot alkaloids, which may result in clinical signs of ergotism, including vasospasm, dysesthesia, renal ischemia, and peripheral ischemia.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturers of itraconazole(1) and ketoconazole(5) state that concurrent administration with ergot alkaloids metabolized by CYP3A4 is contraindicated. The US manufacturer of itraconazole also states that concurrent administration of ergot alkaloids is contraindicated during and two weeks after itraconazole treatment.(1) The manufacturers of dihydroergotamine(3) and ergotamine(4) state that the concurrent use of these agents with strong inhibitors of CYP3A4 such as itraconazole, ketoconazole, or levoketoconazole is contraindicated. The US manufacturer of methylergonovine states that methylergonovine should not be administered with potent CYP3A4 inhibitors such as itraconazole, ketoconazole, or levoketoconazole.(2)

DISCUSSION: Coadministration of dihydroergotamine(3) and ergotamine(4) with potent inhibitors of CYP3A4 such as clarithromycin, erythromycin, indinavir, nelfinavir, ritonavir, and troleandomycin has resulted in ergotism, characterized by vasospasm and ischemia of the extremities. One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated 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.

Ergot Alkaloids/Letermovir

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: Letermovir, a moderate inhibitor of CYP3A4, may inhibit the hepatic metabolism of ergot alkaloids.(1)

CLINICAL EFFECTS: Concurrent use may result in increased levels of the ergot alkaloid, which may result in clinical signs of ergotism, including vasospasm, dysesthesia, renal ischemia, and peripheral ischemia.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The concurrent use of ergotamine derivatives and letermovir is contraindicated.(1) It would be prudent to avoid the concurrent use of all ergot alkaloids and letermovir. Patients receiving concurrent therapy should be monitored for clinical signs of ergotism. One or both agents may need to be discontinued. Patients should be treated symptomatically for ergotism.

DISCUSSION: Letermovir is a moderate inhibitor of CYP3A4. In a study, concurrent administration of letermovir (240 mg once daily) increased the area-under-the curve (AUC), and C24hr of midazolam (1 mg single dose intravenous, a CYP3A4 substrate) by 1.47-fold and 2.74-fold.(1)

Ergot Alkaloids/Posaconazole; Voriconazole

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: Posaconazole(1,2) and voriconazole(3,4) may inhibit the metabolism of the ergot alkaloids by CYP3A4.

CLINICAL EFFECTS: The concurrent use of posaconazole(1,2) or voriconazole (3,4) and ergot alkaloids may result in elevated levels of the ergot alkaloids and ergotism.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The UK(1) and US(2) manufacturers of posaconazole state that the concurrent use of ergot alkaloids is contraindicated. The manufacturer of voriconazole states that the concurrent use of voriconazole and ergot alkaloids is contraindicated.(3) The US manufacturer of methylergonovine states that methylergonovine should not be administered with potent CYP3A4 inhibitors such as voriconazole.(4)

DISCUSSION: Posaconazole has been shown to inhibit the CYP3A4 mediated metabolism of midazolam by 83%.(1) Voriconazole (400 mg every 12 hours for one day, then 200 mg every 12 hours for 8 days) increased the maximum concentration (Cmax) and area-under-curve (AUC) of a single dose of sirolimus (2 mg) by 7-fold and 11-fold, respectively. Ergot alkaloids are metabolized by the same isoenzyme system.(3) One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated 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.

Ergot Alkaloids/Protease Inhibitors

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: The protease inhibitors may inhibit the metabolism of the ergot alkaloids by CYP3A4, including dihydroergotamine, ergotamine, ergonovine, and methylergonovine. (1-13)

CLINICAL EFFECTS: The concurrent administration of a protease inhibitor with an ergot alkaloid may result in elevated levels, clinical effects, and adverse effects of the ergot alkaloids.(1-13) Signs of ergotism may include peripheral vasospasm and ischemia.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The concurrent administration of ergot alkaloids with amprenavir,(1) atazanavir,(2,3) darunavir,(4) fosamprenavir,(5) indinavir, (6) the combination of lopinavir and ritonavir,(7) nelfinavir,(8) nirmatrelvir coadministered with ritonavir,(25) ritonavir, (12) saquinavir,(9,10) and tipranavir coadministered with ritonavir(11) is contraindicated. The US manufacturer of methylergonovine states that methylergonovine should not be administered with potent CYP3A4 inhibitors such as protease inhibitors.(13) Protease inhibitors linked include: amprenavir, atazanavir, ensitrelvir, darunavir, fosamprenavir, indinavir, lopinavir, nelfinavir, nirmatrelvir, ritonavir, saquinavir, and tipranavir.

DISCUSSION: There have been several case reports of ergotism developing in patients receiving concurrent ergotamine derivatives with indinavir,(14) nelfinavir,(15) or ritonavir.(16-23) One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated 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.

Ergot Alkaloids/Selected Macrolide Antibiotics

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: The macrolides may inhibit the hepatic metabolism of ergot alkaloids by inhibition of CYP3A4.(1)

CLINICAL EFFECTS: Concurrent use may result in increased levels of ergot alkaloids, which may result in clinical signs of ergotism, including vasospasm, dysesthesia, renal ischemia, and peripheral ischemia.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of ergotamine(2) and dihydroergotamine (3) state that the concurrent use of these agents with clarithromycin, erythromycin, or troleandomycin is contraindicated. The US manufacturer of methylergonovine states that methylergonovine should not be administered with potent CYP3A4 inhibitors such as the macrolide antibiotics clarithromycin, erythromycin, and troleandomycin.(4) The US manufacturer of clarithromycin states that concurrent administration of ergotamine or dihydroergotamine is contraindicated.(5) It would be prudent to avoid the concurrent use of all ergot alkaloids and macrolide antibiotics that inhibit CYP3A4. Patients receiving concurrent therapy with macrolides and ergot alkaloids should be monitored for clinical signs of ergotism. One or both agents may need to be discontinued. Patients should be treated symptomatically for ergotism.

DISCUSSION: Three case reports have documented clinical signs of ergotism following concomitant therapy with erythromycin and ergotamine. Symptoms included vasospasm, dysesthesia, renal ischemia, and peripheral ischemia. Symptoms occurred within one to seven days of concurrent therapy and with small doses of ergotamine.(6-8) Five case reports have documented peripheral vasospasm following the concurrent administration of ergotamine and troleandomycin. Ergotamine dosages ranged from single dose to long term therapy.(9-12) A similar interaction was reported for ergotamine and troleandomycin(13) and ergotamine and clarithromycin.(14) Other case reports document similar interactions between dihydroergotamine and erythromycin(15-19), troleandomycin(16-19), and ponsinomycin(20). One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated 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.

Ergot Alkaloids/Selected Strong Cyp3a4 Inhibitors

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: Strong inhibitors of CYP3A4 may inhibit the hepatic metabolism of ergot alkaloids.(1-4)

CLINICAL EFFECTS: Concurrent use may result in increased levels of ergot alkaloids, which may result in clinical signs of ergotism, including vasospasm, dysesthesia, renal ischemia, and peripheral ischemia.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The concurrent use of dihydroergotamine,(1,2) ergotamine,(2,3) or methylergonovine(2,4) and strong inhibitors of CYP3A4 is contraindicated. It would be prudent to avoid the concurrent use of all ergot alkaloids and strong inhibitors of CYP3A4. Patients receiving concurrent therapy should be monitored for clinical signs of ergotism. One or both agents may need to be discontinued. Patients should be treated symptomatically for ergotism.

DISCUSSION: Case reports have documented clinical signs of ergotism following concomitant therapy with various ergot alkaloids and strong inhibitors of CYP3A4 such as clarithromycin, erythromycin, indinavir, nelfinavir, ritonavir, and troleandomycin. Selected strong CYP3A4 inhibitors linked include: adagrasib, ceritinib, cobicistat, grapefruit, idelalisib, josamycin, levoketoconazole, lonafarnib, mibefradil, nefazodone, relacorilant, ribociclib, and tucatinib.

Ergot Alkaloids/Telithromycin

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: Telithromycin may inhibit the metabolism of the ergot alkaloids at CYP3A4.(1,2)

CLINICAL EFFECTS: Concurrent use of telithromycin and an ergot alkaloid may result in ergotism (severe vasoconstriction) with possible necrosis of the extremities.(1,2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The UK manufacturer of telithromycin states that the concurrent use of telithromycin and ergot alkaloids is contraindicated.(1) The US manufacturer of telithromycin states that concurrent use is not recommended.(2)

DISCUSSION: Concurrent administration of macrolides such as erythromycin and josamycin with ergot alkaloids has resulted in severe vasoconstriction and necrosis of the extremities. Telithromycin is a potent inhibitor of CYP3A4.(1,2) One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated 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.(3)

Selected Cyp3a4 Substrates/Mifepristone

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: Mifepristone is an inhibitor of CYP3A4 and may increase levels and effects of drugs metabolized by this enzyme.(1)

CLINICAL EFFECTS: Lovastatin, simvastatin and CYP3A4 substrates with a narrow therapeutic window such as alprazolam, cyclosporine, dihydroergotamine, ergotamine, pimozide, quinidine, sirolimus, and tacrolimus or CYP3A4 substrates with a high first pass effect such as oral midazolam, sildenafil, and triazolam are particularly susceptible to significant toxicity.(1,2)

PREDISPOSING FACTORS: Due to the need for continuous therapy and mifepristone's long half-life of 85 hours(1) which leads to accumulation, patients with endogenous Cushing's syndrome may be at an increased risk for toxicity. With pimozide, the risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(3)

PATIENT MANAGEMENT: The US manufacturer of mifepristone for hypercortisolism due to endogenous Cushing's syndrome states use with lovastatin, simvastatin, CYP3A4 substrates with a narrow therapeutic range, or CYP3A4 substrates with a high first pass effect is contraindicated.(1)

DISCUSSION: Administration of mifepristone 1200 mg daily for 10 days followed by a single dose of simvastatin 80 mg led to an increase of simvastatin and simvastatin acid (active metabolite) area-under-curve (AUC) of 10.4-fold and 15.7-fold, respectively.

Serotonergic Agents/Sibutramine

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: Concurrent administration may result in additive effects on serotonin, resulting in serotonin syndrome.

CLINICAL EFFECTS: Concurrent use of sibutramine and agents which effect serotonin may result in serotonin syndrome, a serious and potentially fatal reaction. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity. (1-5)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Sibutramine has been removed from the market by the European Medicines Agency and by regulatory agencies in a number of countries including Australia, Canada, Hong Kong, India, Thailand, United Kingdom and the United States. The Canadian manufacturer of sibutramine formerly stated that concurrent use with antidepressants or serotonergic agents is contraindicated. At least 14 days should elapse between discontinuation of these agents and initiation of sibutramine. Five weeks is required following the discontinuation of fluoxetine.(1) The Australian(2) and UK(3) manufacturers of sibutramine stated that sibutramine is contraindicated within 2 weeks of antidepressant use and should not be used with other serotonergic agents. The US manufacturer of sibutramine stated that in general, sibutramine should not be administered with other serotonergic agents such as the selective serotonin reuptake inhibitors, sumatriptan or dihydroergotamine. However, if concurrent administration is clinically indicated, the patient should be appropriately observed.(4) If concurrent therapy is warranted, patients should be monitored for signs and symptoms of serotonin syndrome. Instruct patients to report muscle twitching, tremors, shivering and stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, trouble with coordination, or severe diarrhea. Patients in whom serotonin syndrome is suspected should receive immediate medical attention.

DISCUSSION: Sibutramine has been removed from the market by the European Medicines Agency and by regulatory agencies in a number of countries including Australia, Canada, Hong Kong, India, Thailand, United Kingdom and the United States. Sibutramine inhibits serotonin reuptake and serotonin syndrome has been reported during concomitant use of selective serotonin reuptake inhibitors and other selective serotonin reuptake inhibitors, sumatriptan, and dihydroergotamine(1-4)

Xanthine Derivatives/Adenosine; Hexobendine; Regadenoson

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: Xanthine derivatives may antagonize the effects of endogenous(1) and exogenous adenosine,(2,3) regadenoson,(4) and hexobendine.(5)

CLINICAL EFFECTS: Concurrent use of a xanthine derivative use may result in decreased effectiveness of adenosine, hexobendine and regadenoson. Aminophylline may increase the risk of adenosine-induced seizures.(3)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients receiving concurrent therapy with adenosine and a xanthine derivative should be monitored for decreased effectiveness of adenosine. The dosage of adenosine may need to be increased. Whenever possible, withhold xanthine derivatives for 5 half-lives prior to using adenosine in cardiac stress tests.(6) Methylxanthines should not be used to reverse the effects of adenosine in patients who experience adenosine-induced seizures.(3) Concurrent therapy with hexobendine and a xanthine oxidase derivative should also be monitored for decreased effectiveness of hexobendine.(5) The US manufacturer of regadenoson recommends that patients avoid methylxanthines (e.g. caffeine, pentoxifylline, and theophylline) for 12 hours prior to regadenoson administration. Aminophylline may be used to attenuate severe and/or persistent adverse reactions to regadenoson.(4)

DISCUSSION: In a study in six healthy subjects, theophylline significantly reduced the heart-rate response to adenosine. In addition, theophylline reduced the amount of abdominal and chest discomfort reported by subjects, allowing significantly higher infusion rates of adenosine.(7) Theophylline has also been reported to antagonize the vasorelaxant action of adenosine in human forearm arterioles.(8) In a study in five subjects, theophylline decreased the amounts of adenosine-induced side effects, including chest pain. There was no change in blood pressure or respiratory rate during concurrent adenosine and theophylline.(9) In a study in ten dog and twelve human subjects, the administration of adenosine after hexobendine increased coronary sinus blood flow. Aminophylline administration significantly decreased the coronary vasodilation response to adenosine and hexobendine.(5) In a study in ten healthy subjects, caffeine reduced the mean adenosine-induced increases in systolic blood pressure by 7.2 mmHg and heart rate by 8.4 beats/min when compared to placebo.(2) In another study in ten healthy subjects, caffeine was shown to lower the adenosine-induced response of blood pressure and heart rate.(3) Caffeine has also been reported to reduced adenosine-induced changes in minute ventilation and tidal volume.(3) Aminophylline has been shown to shorten the duration of coronary blood flow response to regadenoson.(3) Coronary flow reserve was 8% lower in patients who received caffeine (200 mg single dose) 2 hours prior to regadenoson administration when compared to subjects who received placebo instead of caffeine.(4)

Xanthine Derivatives/Dipyridamole Injectable

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: The xanthine derivatives are adenosine receptor antagonists. Concurrent administration may inhibit dipyridamole-induced increases in endogenous plasma adenosine levels, thus decreasing dipyridamole's vasodilator effects.(1)

CLINICAL EFFECTS: Concurrent administration may result in a decrease in dipyridamole's vasodilator effects. This may produce false-negative results during dipyridamole-thallium imaging tests.(1-3)

PREDISPOSING FACTORS: In patients with congestive heart failure and decreased hepatic function, the metabolism of xanthine derivatives may be decreased. These patients may need a longer xanthine-free period prior to dipyridamole-thallium imaging tests.(2)

PATIENT MANAGEMENT: Patients scheduled for dipyridamole-thallium imaging tests should have a xanthine-free period (including caffeine-containing products) for at least 24 hours prior to their exam.(3)

DISCUSSION: In a study in eight male subjects with documented coronary artery disease, intravenous dipyridamole administered during a dipyridamole-thallium 201 SPECT image test produced a significant increase in heart rate, a decrease in blood pressure, and angina in seven patients and ST segment depression in four patients. SPECT imaging showed reversible perfusion defects in myocardial segments supplied by stenotic coronary arteries. When the exam was repeated when the subjects were receiving therapeutic dosages of theophylline, there was no appearance of angina, ST depression, or hemodynamic changes and SPECT imaging shown total absence of reversible perfusion defects.(1) A study in eight patients with coronary artery disease evaluated the effects of caffeine on dipyridamole-201Tl myocardial imaging. The administration of dipyridamole alone resulted in chest pain and ST-segment depression in four patients. Concurrent caffeine infusion decreased the dipyridamole-induced decrease in blood pressure and heart rate. No patients experience chest pain or ST-segment depression. Six patients had false negative test results.(2) Another study found that the attenuation of the hemodynamic response to dipyridamole by caffeine was dose-dependent.(3)

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

Ergot Alkaloids/Moderate Cyp3a4 Inhibitors

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

MECHANISM OF ACTION: Moderate CYP3A4 inhibitors may inhibit the metabolism of ergot alkaloids.

CLINICAL EFFECTS: Concurrent use of a moderate CYP3A4 inhibitor may result in increased levels of the ergot alkaloid, which may result in clinical signs of ergotism, including vasospasm, dysesthesia, renal ischemia, and peripheral ischemia.

PREDISPOSING FACTORS: Patients receiving the maximum recommended (or higher than recommended) dosages of ergot alkaloids may be at a higher risk of adverse effects from this combination.

PATIENT MANAGEMENT: When possible, avoid the concurrent use of moderate CYP3A4 inhibitors in patients taking ergot alkaloids. If concurrent use is warranted, consider reducing the dose of the ergot alkaloid during concurrent therapy. Patients receiving concurrent therapy should be monitored for and instructed to report any signs of ergotism.

DISCUSSION: Coadministration of dihydroergotamine and ergotamine with potent inhibitors of CYP3A4 such as clarithromycin, erythromycin, indinavir, nelfinavir, ritonavir, and troleandomycin has resulted in ergotism, characterized by vasospasm and ischemia of the extremities. Inhibition of ergot alkaloid metabolism by moderate inhibitors would also be expected, but to a lesser degree. Moderate CYP3A4 inhibitors linked to this monograph are aprepitant, avacopan, berotralstat, clofazimine, conivaptan, crizotinib, diltiazem, dronedarone, duvelisib, fedratinib, fluconazole, fluvoxamine, fosnetupitant, imatinib, isavuconazonium, lenacapavir, netupitant, nilotinib, nirogacestat, rilzabrutinib, schisandra, tofisopam, treosulfan and verapamil.

Ergot Alkaloids/Nitrates

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

MECHANISM OF ACTION: Decreased first-pass metabolism of ergot alkaloids. Ergot alkaloids may precipitate angina pectoris.

CLINICAL EFFECTS: Increased standing systolic blood pressure and angina attacks may occur.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid administration of ergot alkaloids to patients receiving nitroglycerin for angina. When it is necessary to give this combination, monitor the patient for increased effects of the ergot alkaloid. Reduce the dose of ergot alkaloid as necessary.

DISCUSSION: Dihydroergotamine has been reported to precipitate angina pectoris. Nitroglycerin administration to patients receiving dihydroergotamine increased the plasma dihydroergotamine level and area under the plasma concentration-time curve. An increase in the mean standing systolic blood pressure was measured.

Ergot Alkaloids/Stiripentol

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

MECHANISM OF ACTION: Stiripentol may inhibit the metabolism of ergot alkaloids by CYP3A4.(1)

CLINICAL EFFECTS: Concurrent use of stiripentol may result in elevated levels of ergot alkaloids, which may result in ergotism with the possibility of necrosis of the extremities.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The UK manufacturer of stiripentol states that concurrent use of ergot alkaloids should be avoided unless strictly necessary.(1)

DISCUSSION: Stiripentol has been shown to inhibit CYP3A4. In a pediatric study, concurrent administration of stiripentol and clobazam (a CYP3A4 substrate) increased clobazam plasma levels by approximately 2- to 3-fold.(1)

Ergot Alkaloids/Sympathomimetics

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

MECHANISM OF ACTION: Concurrent use of ergot alkaloids and sympathomimetics may result in additive or synergistic effect on peripheral blood vessels.

CLINICAL EFFECTS: Concurrent use of ergot alkaloids and sympathomimetics may result in increased blood pressure due to peripheral vasoconstriction.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: When possible, avoid the concurrent use of ergot alkaloids and sympathomimetics. If concurrent use is warranted, monitor blood pressure and for signs of vasoconstriction. Decreasing the dose of one or both drugs may be necessary.

DISCUSSION: There have been reports of severe vasoconstriction resulting in gangrene in patients receiving intravenous ergonovine with dopamine or norepinephrine.

Selected Cyp1a2 Substrates/Viloxazine

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

MECHANISM OF ACTION: Viloxazine is a strong inhibitor of CYP1A2 and may increase the total exposure of sensitive CYP1A2 substrates.(1) The FDA defines strong inhibition as an increase in drug area-under-curve (AUC) greater than 5-fold.(2)

CLINICAL EFFECTS: Concurrent use of viloxazine with drugs primarily metabolized by CYP1A2 may lead to elevated drug levels and increase the risk of adverse reactions associated with the CYP1A2 substrate.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Drugs linked to this monograph are moderately sensitive to CYP1A2 inhibition. Coadministration of viloxazine with moderately sensitive CYP1A2 substrates is not recommended. If coadministered, dose reduction of the CYP1A2 substrate may be warranted.(1)

DISCUSSION: Concomitant use of viloxazine significantly increases the total exposure, but not peak exposure, of sensitive CYP1A2 substrates, which may increase the risk of adverse reactions associated with these CYP1A2 substrates. In a study, viloxazine increased the AUC of caffeine by almost 6-fold.(1) Though not designed to evaluate drug interactions, the open-label portion of a pediatric randomized controlled trial looking at the association of riluzole concentrations with efficacy and adverse effects found that fluvoxamine (a strong CYP1A2 inhibitor) increased riluzole concentrations by about 2-fold.(3) CYP1A2 substrates linked to this monograph include: caffeine and riluzole.(2,4)

Selected Moderate And Weak Cyp1a2 Inhibitors/Tizanidine

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

MECHANISM OF ACTION: Moderate and weak CYP1A2 inhibitors may inhibit the metabolism of tizanidine by CYP1A2.(1)

CLINICAL EFFECTS: Concurrent use of moderate and weak CYP1A2 inhibitors may result in elevated levels of and effects from tizanidine, including hypotension, bradycardia, drowsiness, sedation, and decreased psychomotor function.

PREDISPOSING FACTORS: The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(2)

PATIENT MANAGEMENT: The US manufacturer of tizanidine states that concurrent use of tizanidine with inhibitors of CYP1A2 should be avoided.(3) If adverse reactions such as hypotension, bradycardia or excessive drowsiness occur, reduce tizanidine dosage or discontinue tizanidine therapy.(3)

DISCUSSION: In a study, cannabidiol 750 mg twice daily (a weak CYP1A2 inhibitor) increased the maximum concentration (Cmax) and area-under-curve (AUC) of a 200 mg single dose of caffeine (a sensitive CYP1A2 substrate) by 15% and 95%, respectively.(1) In a study in 10 healthy subjects, concurrent fluvoxamine, a strong inhibitor of CYP1A2, increased tizanidine Cmax, AUC, and half-life (T1/2) by 12-fold, 33-fold, and 3-fold, respectively. Significant decreases in blood pressure and increases in drowsiness and psychomotor impairment occurred.(3) In a study in 10 healthy subjects, concurrent ciprofloxacin, a strong inhibitor of CYP1A2, increased tizanidine Cmax and AUC by 7-fold and 10-fold, respectively. Significant decreases in blood pressure and increases in drowsiness and psychomotor impairment occurred.(3) Moderate CYP1A2 inhibitors linked to this monograph include: centanafadine, dipyrone, fexinidazole, genistein, methoxsalen, phenylpropanolamine, pipemidic acid, propranolol, rucaparib, and troleandomycin. Weak CYP1A2 inhibitors linked to this monograph include: allopurinol, artemisinin, belumosudil, caffeine, cannabidiol, curcumin, dan-shen, disulfiram, Echinacea, ginseng, parsley, piperine, ribociclib, simeprevir, thiabendazole, and triclabendazole.(4)

Selected Sensitive Cyp3a4 Substrates/Voxelotor

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

MECHANISM OF ACTION: Voxelotor is an inhibitor of CYP3A4 and may decrease the metabolism of drugs metabolized by the CYP3A4 enzyme.

CLINICAL EFFECTS: Concurrent use of voxelotor may lead to increased serum levels and adverse effects of drugs sensitive to inhibition of the CYP3A4 pathway.(1)

PREDISPOSING FACTORS: A greater risk for serious adverse events would be expected from drugs having a narrow therapeutic window.

PATIENT MANAGEMENT: The manufacturer of voxelotor states that co-administration of sensitive CYP3A4 substrates with a narrow therapeutic index should be avoided. If concomitant use is unavoidable, consider dose reduction of the sensitive substrate.(1)

DISCUSSION: In a study, voxelotor increased the AUC of a single dose of midazolam by 1.6-fold. After multiple doses of midazolam, a 2.5-fold increase in AUC is predicted.(1) Sensitive CYP3A4 substrates with a narrow therapeutic index linked to this monograph include: avanafil, conivaptan, cyclosporine, dihydroergotamine, eplerenone, ergotamine, everolimus, felodipine, fentanyl, lomitapide, lovastatin, methylergonovine, midazolam, nisoldipine, sildenafil, simvastatin, ticagrelor, tolvaptan, triazolam, and vardenafil.(2,3)

Selected Sensitive Cyp3a4; Cyp2c19 Substrates/Apalutamide

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

MECHANISM OF ACTION: Apalutamide may induce the metabolism of sensitive CYP3A4 or CYP2C19 substrates.(1)

CLINICAL EFFECTS: Concurrent use of apalutamide with drugs primarily metabolized by CYP3A4 or CYP2C19 can result in lower exposure to these medications.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturer of apalutamide recommends substitution for medications primarily metabolized by CYP3A4 or CYP2C19 when possible or evaluate for loss of activity.(1)

DISCUSSION: Coadministration of apalutamide with single oral doses of sensitive CYP substrates resulted in a 92% decrease in the area-under-curve (AUC) of midazolam (a CYP3A4 substrate) and an 85% decrease in the AUC of omeprazole (a CYP2C19 substrate).(1) Selected sensitive CYP3A4 substrates linked to this monograph: astemizole, dihydroergotamine, ergonovine, ergotamine, and terfenadine. Selected sensitive CYP2C19 substrates linked to this monograph: fosphenytoin, mephenytoin, and phenytoin.(2,3)

Sensitive Cyp3a4; Cyp2c9; Cyp2c19 Substrates/Enzalutamide

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

MECHANISM OF ACTION: Enzalutamide may induce the metabolism of agents metabolized by CYP3A4, CYP2C9, and CYP2C19.(1)

CLINICAL EFFECTS: Concurrent use of enzalutamide with agents metabolized by CYP3A4, CYP2C9, and CYP2C19 may result in decreased levels and effectiveness of these agents.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid concurrent use of agents metabolized by CYP3A4, CYP2C9, or CYP2C19 that have a narrow therapeutic index with enzalutamide. If concurrent use is required, consider increased monitoring of the affected agent.(1) Dosage adjustments may be required.

DISCUSSION: In a clinical trial in healthy subjects, enzalutamide was shown to reduce the area-under-curve (AUC) of midazolam (a sensitive CYP3A4 substrate), warfarin (a sensitive CYP2C9 substrate), and omeprazole (a sensitive CYP2C19 substrate.(1) A case report in a 77-year-old Caucasian male was initiated on 160 mg of enzalutamide after being stable on warfarin with an INR of 3.5. The INR dropped to 1.4 after approximately 20 days on enzalutamide therapy. Due to the drop in INR, the warfarin dose was increased by 50% which lead to a therapeutic INR. When enzalutamide was discontinued, the warfarin dose was decreased by 33% to remain at a therapeutic level. Upon reinitiation, the warfarin dose was increased once by 50% to achieve a therapeutic INR.(2) Sensitive CYP3A4 substrates with narrow therapeutic indexes include: astemizole, cisapride, clarithromycin, cyclosporine, dihydroergotamine, ergonovine, ergotamine, pimozide, sirolimus, tacrolimus, temsirolimus, and terfenadine.(1,3,4) Sensitive CYP2C9 substrates with narrow therapeutic indexes include: warfarin.(1,3) Sensitive CYP2C19 substrates with narrow therapeutic indexes include: S-mephenytoin.(1,3)

Theophylline Derivatives/Cimetidine

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

MECHANISM OF ACTION: Cimetidine inhibits the metabolism of theophylline by CYP1A2.(1-10) The duration of cimetidine's inhibitory action is uncertain. Short-term cimetidine therapy appears to reverse rapidly(2) but may persist in prolonged therapy. Increased pentoxifylline serum levels may be the result of an increase in the oral bioavailability of pentoxifylline.(11)

CLINICAL EFFECTS: Concurrent cimetidine and theophylline derivative therapy may result in elevated theophylline derivative concentration levels, prolonged elimination half-life, and decreased clearance.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Theophylline derivative blood levels should be very closely monitored if cimetidine therapy is to be initiated, changed, or discontinued. Theophylline has a narrow therapeutic range; therefore, dosage reductions up to 30-50%(4) should be considered to prevent intoxication when cimetidine therapy is started. Antacids, famotidine, or possibly ranitidine might be more judicious choices than cimetidine in patients receiving theophylline derivatives.

DISCUSSION: It is well documented that cimetidine impairs the elimination of theophylline when the two agents are co-administered to patients.(1-10, 12-22) This interaction has been noted by a variety of routes including continuous intravenous infusion.(22) Reports indicate that with concurrent cimetidine, theophylline plasma concentrations increase, theophylline half-life is prolonged from 29% to 73%(1-3;9,12-14) and theophylline clearance is decreased by 18.5% to 46%.(1-3,9,13,23) Age and smoking do not appear to affect the magnitude of the interaction.(17,18,20) Significant changes can be seen within 24 hours(3,5) and may progress as co-therapy continues.(3) A study involving ten healthy patients demonstrated that concomitant administration of cimetidine significantly decreased the plasma clearance of oxtriphylline.(24) Aminophylline is involved in a similar interaction as theophylline as seen in one case report.(25) In one report cimetidine also decreased the clearance and prolonged the half-life of caffeine.(26,27) A study demonstrated that cimetidine caused a significant increase in plasma levels of pentoxifylline.(11) Information on ranitidine is conflicting. Several studies have shown that ranitidine does not influence theophylline.(9,15,16,19,28,29) One case report noted toxic theophylline levels after ranitidine;(30) however, this case report has been challenged.(31) In another case report, theophylline levels rose from 16.6 mcg/ml to 39.7 mcg/ml(32) when the patient was given ranitidine. Other reports have also noted a reduction in theophylline elimination by ranitidine.(33,34) Famotidine has shown to have no effect on theophylline metabolism in a clinical trial;(35) however, there is one case report of decreased theophylline clearance during famotidine therapy.(36) Dyphylline, a theophylline derivative that is not converted to theophylline in vivo, is not to be expected to interact with cimetidine. A study showed that cimetidine increased the average steady state plasma concentration of pentoxifylline and its metabolite by 25% and 30%, respectively.(37)

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

Caffeine-Containing Products/Migalastat

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

MECHANISM OF ACTION: The mechanism of this interaction is unknown.

CLINICAL EFFECTS: Concurrent use of a caffeine-containing product may result in decreased levels and effectiveness of migalastat.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid coadministration of migalastat with caffeine-containing products. Do not administer caffeine-containing products within 2 hours before and 2 hours after taking migalastat.(1)

DISCUSSION: Coadministration of migalastat with caffeine 190 mg decreased the migalastat maximum concentration (Cmax) by 60% and area-under-curve (AUC) by 55%.(1)

Selected Xanthine Derivatives/Fluvoxamine

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

MECHANISM OF ACTION: Fluvoxamine may inhibit the metabolism of the xanthine derivatives by CYP1A2.(1,2)

CLINICAL EFFECTS: Concurrent use of fluvoxamine and xanthine derivatives may result in elevated levels of the xanthine derivative and toxicity.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of fluvoxamine recommends that the dose of theophylline be decreased to one-third of the usual daily dose in patients receiving concurrent therapy. Theophylline levels should be closely monitored and patients should be observed for signs of theophylline toxicity.(3) The dosage of theophylline may need to be adjusted if fluvoxamine is discontinued. Patients receiving fluvoxamine should be instructed to consume caffeine containing beverages and/or medications with caution.

DISCUSSION: In a study in 12 healthy subjects, the administration of a single dose of theophylline ethylenediamine (300 mg) on Day 4 of fluvoxamine (50 mg Day 1, 100 mg daily Days 2-6) decreased theophylline total clearance by 70%. The half-life of theophylline increased 2.3-fold (from 6.6 hours to 22 hours).(1) In a study in 12 healthy males, the administration of a single dose of theophylline (375 mg given as 442 mg aminophylline) with fluvoxamine (50 mg twice daily at steady state) decreased theophylline clearance by 3-fold.(3) Fluvoxamine has been shown to inhibit the metabolism of theophylline in vitro.(2) There are four case reports of theophylline toxicity during concurrent fluvoxamine therapy.(4-7) In a study in eight healthy subjects, the administration of a single dose of caffeine (200 mg) on Day 8 of fluvoxamine (50 mg daily Days 1-4, 100 mg daily Days 5-12) decreased caffeine clearance by 80%. The half-life of caffeine increased 5.2-fold (from 5 hours to 31 hours).(8) In a study, seven reports of impaired caffeine clearance were reported in patients whom received single 250mg doses of caffeine together with fluvoxamine (four doses of 100mg over two days). Fluvoxamine reduced the apparent oral clearance of caffeine by 91.3%, and prolonged its elimination half-life by 11.4-fold (from 4.9 hours to 56 hours). There were no changes in the pharmacodynamic effects of caffeine.(9)

Theophylline Derivatives/Lithium

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

MECHANISM OF ACTION: Theophylline derivatives increase the renal excretion of lithium.

CLINICAL EFFECTS: Decreased levels of lithium which may result in decreased clinical effectiveness.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Lithium levels and response should be monitored in patients in whom theophylline therapy is initiated or withdrawn. Patients receiving concurrent therapy should be monitored for increased adverse effects.

DISCUSSION: In a study involving ten volunteers, the concurrent administration of lithium and theophylline resulted in a significant decrease in lithium serum levels. Upon discontinuation of theophylline, lithium levels and half-life increased, and the clearance of lithium decreased. Individual variability in these parameters was significant. The overall incidence of adverse effects was significantly greater with concurrent therapy including restlessness, tremor, and anorexia. In another study in ten normal subjects, lithium (1200 mg/day for seven days) was administered and it was reported that theophylline infusion (dosed to achieve a plasma level of 14 mcg/ml) increased lithium clearances by 51%. In a case report, reduced lithium levels as well as worsening of manic symptoms occurred after increasing doses of theophylline were administered. It has been shown that aminophylline increases the lithium/creatinine clearance ratio, which may result in decreased serum lithium below the therapeutic level. Caffeine withdrawal has been reported to increase lithium levels in several case reports. This interaction is most important to consider in patients who have been previously sensitive to relapse with decreased lithium levels and in whom levels are maintained at the therapeutic/prophylactic borderline.

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• Cerebral ischemia
• Coronary artery disease
• Disease of liver
• Ergot alkaloid toxicity
• Hypertension
• Kidney disease with reduction in glomerular filtration rate (GFr)
• Lactation
• Peripheral ischemia
• Peripheral vascular disease
• Pregnancy
• Raynaud's phenomenon
• Sepsis
• Severe pruritus
• Thrombophlebitis

• Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
• Chronic kidney disease stage 5 (failure) GFr<15 ml/min
• Necrotizing enterocolitis
• Peptic ulcer
• Pleural fibrosis
• Porphyria
• Pulmonary fibrosis
• Retroperitoneal fibrosis
• Severe hepatic disease

• Cardiac arrhythmia
• Diarrhea
• Seizure disorder

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More Frequent

• Peripheral edema

Rare or Very Rare

• Acute cognitive impairment
• Angina
• Cardiac arrhythmia
• Coronary artery spasm
• Extrasystoles
• Hypertension
• Hypotension
• Ischemic colitis
• Miosis
• Peripheral vasoconstriction
• Pleural fibrosis
• Pulmonary fibrosis
• Retroperitoneal fibrosis
• Valvular sclerosis
• Visual changes

More Frequent

• Diarrhea
• Dizziness
• Drowsy
• Gastrointestinal irritation
• Insomnia
• Nausea
• Nervousness
• Vomiting
• Xerostomia

Less Frequent

• Dyspnea
• Excitement
• Flushing
• Headache disorder
• Hyperhidrosis
• Paresthesia
• Skin rash

Rare or Very Rare

• Agitation
• Hyperesthesia
• Hyperglycemia
• Irritability
• Nausea
• Scotomata
• Symptoms of anxiety
• Symptoms of anxiety
• Tachycardia
• Tinnitus
• Tremor
• Vomiting

No enhanced messaging available.

No enhanced messaging available.

Retarded fetal growth and increases in intrauterine death and resorption were reported in animals receiving ergotamine. It has been postulated that such fetotoxicity is associated with drug-induced increases in uterine motility and vasoconstriction in the placental vasculature. Ergotamine is contraindicated in women who are or may become pregnant.

There are no adequate and well-controlled studies in pregnant women. In studies performed in adult animals, caffeine (as caffeine base) administered to pregnant mice as sustained-release pellets at 50 mg/kg (less than the maximum IV loading dose for neonates on a mg/m2 basis) during the period of organogenesis caused a low incidence of cleft palate and exencephaly in fetuses. Based on data from a large retrospective epidemiologic study and from a large retrospective case-control study in humans, it appears that use of caffeine during pregnancy has little, if any, effect on the outcome of pregnancy. Although caffeine use during pregnancy does not appear to be associated with substantial risk, most clinicians recommend that pregnant women avoid or limit their consumption of foods, beverages, and drugs containing caffeine, since caffeine crosses the placenta.

Ergotamine is distributed into milk and may cause vomiting, diarrhea, weak pulse, unstable blood pressure, and seizures in nursing infants. Although ergot alkaloids have been reported to inhibit maternal pituitary prolactin secretion, decreased lactation has not been reported to date with ergotamine. Because of the potential for serious adverse reactions to ergotamine in nursing infants, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.

Caffeine is distributed into the milk of nursing women. Milk-to-plasma ratios of 0.5-0.76 have been reported. The amount of caffeine ingested from usual quantities of caffeinated beverages is considered compatible with breast-feeding; however, caffeine may accumulate in nursing infants following moderate to heavy maternal consumption of caffeine, resulting in irritability and poor sleeping patterns.

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