Drug Interactions between chloroquine and Malarone

GENERALLY AVOID: Theoretically, grapefruit and grapefruit juice may increase the plasma concentrations of hydroxychloroquine or chloroquine and the risk of toxicities such as QT interval prolongation and ventricular arrhythmias. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall induced by certain compounds present in grapefruit. Following coadministration with cimetidine, a weak to moderate CYP450 3A4 inhibitor, a 2-fold increase in chloroquine exposure occurred. Since chloroquine and hydroxychloroquine have similar structures and metabolic elimination pathways, a similar interaction may be observed with hydroxychloroquine. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. Pharmacokinetic interactions involving grapefruit juice are also subject to a high degree of interpatient variability, thus the extent to which a given patient may be affected is difficult to predict.

ADJUST DOSING INTERVAL: Administration with food or milk may reduce the incidence of hydroxychloroquine-related gastrointestinal adverse effects.

MANAGEMENT: Although clinical data are lacking, it may be advisable to avoid the consumption of grapefruit, grapefruit juice, and any supplement containing grapefruit extract during hydroxychloroquine or chloroquine therapy. Hydroxychloroquine should be administered with food or milk to reduce the occurrence of gastrointestinal upset.

ADJUST DOSING INTERVAL: Food, particularly high-fat food, significantly enhances the oral absorption and bioavailability of atovaquone. In 16 healthy volunteers, administration of a single 750 mg dose of atovaquone suspension following a standard breakfast (23 g fat: 610 kCal) resulted in an approximately 3.4-fold increase in the mean peak plasma concentration (Cmax) and a 2.5-fold increase in the mean area under the plasma concentration-time curve (AUC) of atovaquone compared to administration following an overnight fast. In a study consisting of 19 HIV-infected volunteers receiving atovaquone suspension 500 mg/day, Cmax and AUC of atovaquone increased by 72% and 66%, respectively, in the fed state relative to the fasting state.

MANAGEMENT: To ensure maximal oral absorption, atovaquone products (suspension, tablet, or in combination with proguanil) should be administered with a meal or milky drink, or enteral nutrition at the same time(s) each day. Because plasma atovaquone concentrations have been shown to correlate with the likelihood of successful treatment and in some cases, survival, alternative therapies may be appropriate for patients who have difficulty taking atovaquone with food.

The recommended maximum number of medicines in the 'antimalarials' category to be taken concurrently is usually one. Your list includes two medicines belonging to the 'antimalarials' category:

• chloroquine
• Malarone (atovaquone/proguanil)

Note: In certain circumstances, the benefits of taking this combination of drugs may outweigh any risks. Always consult your healthcare provider before making changes to your medications or dosage.