Drug Interactions between artemether / lumefantrine and Flagyl

CONTRAINDICATED: Use of alcohol or products containing alcohol during nitroimidazole therapy may result in a disulfiram-like reaction in some patients. There have been a few case reports involving metronidazole, although data overall are not convincing. The presumed mechanism is inhibition of aldehyde dehydrogenase (ALDH) by metronidazole in a manner similar to disulfiram. Following ingestion of alcohol, inhibition of ALDH results in increased concentrations of acetaldehyde, the accumulation of which can produce an unpleasant physiologic response referred to as the 'disulfiram reaction'. Symptoms include flushing, throbbing in head and neck, throbbing headache, respiratory difficulty, nausea, vomiting, sweating, thirst, chest pain, palpitation, dyspnea, hyperventilation, tachycardia, hypotension, syncope, weakness, vertigo, blurred vision, and confusion. Severe reactions may result in respiratory depression, cardiovascular collapse, arrhythmia, myocardial infarction, acute congestive heart failure, unconsciousness, convulsions, and death. However, some investigators have questioned the disulfiram-like properties of metronidazole. One study found neither elevations in blood acetaldehyde nor objective or subjective signs of a disulfiram-like reaction to ethanol in six subjects treated with metronidazole (200 mg three times a day for 5 days) compared to six subjects who received placebo.

MANAGEMENT: Because clear evidence is lacking concerning the safety of ethanol use during nitroimidazole therapy, patients should be apprised of the potential for interaction. Consumption of alcoholic beverages and products containing propylene glycol is specifically contraindicated during and for at least 3 days after completion of metronidazole and benznidazole therapy according to their product labeling.

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of artemether and lumefantrine. The mechanism is decreased clearance due to inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. High plasma levels of artemether and lumefantrine may increase the risk of QT interval prolongation and ventricular arrhythmias including torsade de pointes. In clinical trials, asymptomatic prolongation of the Fridericia-corrected QT interval (QTcF) by more than 30 msec from baseline was reported in approximately one-third of patients treated with artemether-lumefantrine, and prolongation by more than 60 msec was reported in more than 5% of patients. A few patients (0.4%) in the adult/adolescent population and no patient in the infant/children population experienced a QTcF greater than 500 msec. However, the possibility that these increases were disease-related cannot be ruled out. In a study of healthy adult volunteers, administration of the six-dose regimen of artemether-lumefantrine was associated with mean changes in QTcF from baseline of 7.45, 7.29, 6.12 and 6.84 msec at 68, 72, 96, and 108 hours after the first dose, respectively. There was a concentration-dependent increase in QTcF for lumefantrine. No subject had a greater than 30 msec increase from baseline nor an absolute increase to more than 500 msec.

ADJUST DOSING INTERVAL: Food enhances the oral absorption of artemether and lumefantrine. In healthy volunteers, the relative bioavailability of artemether increased by two- to threefold and that of lumefantrine by sixteenfold when administered after a high-fat meal as opposed to under fasted conditions.

MANAGEMENT: Patients receiving artemether-lumefantrine therapy should avoid the consumption of grapefruits and grapefruit juice. To ensure maximal oral absorption, artemether-lumefantrine should be taken with food. Inadequate food intake can increase the risk for recrudescence of malaria. Patients who are averse to food during treatment should be closely monitored and encouraged to resume normal eating as soon as food can be tolerated.