Drug Interactions between Aldoril D50 and Multaq

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of dronedarone. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. According to the product labeling, administration with grapefruit juice resulted in a 2.5-fold increase in dronedarone peak plasma concentration and a 3-fold increase in systemic exposure. Because dronedarone is associated with concentration-dependent prolongation of the QT interval, increased levels may potentiate the risk of ventricular arrhythmias such as torsade de pointes and sudden death.

ADJUST DOSING INTERVAL: Food increases the oral bioavailability of dronedarone. The mechanism of interaction is unknown. According to the product labeling, the absolute bioavailability of dronedarone increases from about 4% when administered in the fasted state to approximately 15% when administered with a high-fat meal.

MANAGEMENT: Patients treated with dronedarone should avoid consumption of grapefruit, grapefruit juice, and any supplement containing grapefruit extract. Dronedarone should be taken twice daily with the morning and evening meals.

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MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia.

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MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia.

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ADJUST DOSING INTERVAL: The oral bioavailability and pharmacologic effects of methyldopa may be decreased during concurrent administration with iron-containing products. The proposed mechanism is chelation of methyldopa by the iron cation, forming an insoluble complex that is poorly absorbed from the gastrointestinal tract. In one study, five hypertensive patients receiving chronic methyldopa therapy (250 mg to 1500 mg daily) all had elevated blood pressure following the addition of ferrous sulfate 325 mg three times daily for 2 weeks. The systolic pressure had increased by more than 15 mmHg in three of the patients and the diastolic pressure increased by more than 10 mmHg in two. Blood pressure returned to baseline within 7 days of discontinuing the iron. In 12 normal subjects, administration of methyldopa 500 mg with ferrous sulfate 325 mg or ferrous gluconate 600 mg resulted in an 88% and 79% reduction, respectively, in the renal excretion of unmetabolized, free methyldopa compared to administration of methyldopa alone. In another study, administration of ferrous sulfate simultaneously with methyldopa reduced the bioavailability of methyldopa by 83%, while administration one hour or two hours before methyldopa reduced its bioavailability by 55% and 42%, respectively.

MANAGEMENT: Until more information is available, patients receiving methyldopa in combination with iron-containing products should be advised to separate the times of administration by as much as possible. Patients should be monitored closely for altered hypertensive effect and methyldopa dosage increased as necessary. Selection of an alternative antihypertensive therapy may be necessary.

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