Drug Interaction Report

CONTRAINDICATED: Theoretical concerns exist that initiating treatment with fingolimod may potentiate the risk of torsade de pointes arrhythmia associated with the use of class IA (e.g., disopyramide, quinidine, procainamide) and class III (e.g., amiodarone, dofetilide, ibutilide, sotalol) antiarrhythmic agents. Fingolimod can cause a decrease in heart rate during initiation of therapy that is apparent within an hour of the first dose and maximal at approximately 6 hours postdose in most cases, but occasionally up to 20 hours after the first dose. Further, but smaller decreases in heart rate may occur after the second dose, although heart rate eventually returns to baseline within one month of chronic treatment. The mean decrease in heart rate in patients receiving fingolimod 0.5 mg at 6 hours after the first dose was approximately 13 beats per minute (bpm). Heart rates below 40 bpm were rarely observed. In controlled clinical trials, adverse reactions of symptomatic bradycardia (hypotension, dizziness, fatigue, palpitations, chest pain) following the first dose were reported in 0.5% of patients receiving fingolimod 0.5 mg, compared to no patient on placebo. Initiation of fingolimod treatment has also resulted in transient AV conduction delays. First- and second-degree AV block (prolonged PR interval on ECG) following the first dose were each reported in 0.1% of patients receiving fingolimod 0.5 mg, compared to no patient on placebo. In a study of 698 patients with available 24-hour Holter monitoring data after their first dose, second degree AV blocks, usually Mobitz type I (Wenckebach), were reported in 3.7% of patients receiving fingolimod 0.5 mg and 2% of patients receiving placebo. Bradycardia and conduction abnormalities were usually transient and asymptomatic, and resolved within the first 24 hours on treatment, but they occasionally required treatment with atropine or isoproterenol.

MANAGEMENT: The use of fingolimod in patients with arrhythmias requiring treatment with class IA or class III antiarrhythmic agents has not been studied and is considered contraindicated.

GENERALLY AVOID: Grapefruit juice may significantly increase the plasma concentrations of orally administered amiodarone. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In 11 nonsmoking, healthy volunteers, grapefruit juice (300 mL with drug administration, then 3 hours and 9 hours later) increased the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of amiodarone (17 mg/kg single dose) by 84% and 50%, respectively, compared to water. Formation of the pharmacologically active metabolite, N-desethylamiodarone (N-DEA), was completely inhibited. Clinically, this interaction can lead to altered efficacy of amiodarone, since antiarrhythmic properties of amiodarone and N-DEA appear to differ. In the study, mean increases in PR and QTc intervals of 17.9% and 11.3%, respectively, were observed 6 hours postdose with water, while increases of 10.2% and 3.3%, respectively, were observed after administration with grapefruit juice.

ADJUST DOSING INTERVAL: Food increases the rate and extent of absorption of amiodarone. The mechanism appears to involve the effect of food-induced physiologic changes on drug release from its formulation. In 30 healthy volunteers, administration of a single 600 mg dose of amiodarone following a high-fat meal resulted in a Cmax and AUC that were 3.8 and 2.4 times the respective values under fasting conditions. The time to reach peak plasma concentration (Tmax) was decreased by 37%, indicating an increased rate of absorption. Mean Cmax and AUC for the active metabolite, N-DEA, also increased by 32% and 55%, respectively, but there was no change in the Tmax.

MANAGEMENT: Patients treated with oral amiodarone should avoid consumption of grapefruits and grapefruit juice. In addition, oral amiodarone should be administered consistently with regard to meals.