Drug Interaction Report

MONITOR: Coadministration with deferasirox may decrease the plasma concentrations of drugs that are substrates of the CYP450 3A4 isoenzyme. The mechanism may involve induction of CYP450 3A4 activity by deferasirox, although in vitro, the drug has been shown to inhibit CYP450 3A4. In healthy volunteers, administration of the CYP450 3A4 probe substrate midazolam in combination with deferasirox resulted in a reduction of midazolam peak concentration by 23% and systemic exposure by 17%. In the clinical setting, this effect may be more pronounced.

MANAGEMENT: Caution is advised if deferasirox must be used concomitantly with medications that undergo metabolism by CYP450 3A4, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever deferasirox is added to or withdrawn from therapy.

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of eplerenone. The primary mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. Inhibition of hepatic CYP450 3A4 may also contribute. In drug interaction studies, administration of a single 100 mg dose of eplerenone in combination with grapefruit juice resulted in a 25% increase in eplerenone systemic exposure (AUC). High blood levels of eplerenone can increase the risk of side effects including hyperkalemia. 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.

MANAGEMENT: It may be advisable for patients to avoid the consumption of grapefruit, grapefruit juice, or supplements that contain grapefruit during treatment with eplerenone.

ADJUST DOSING INTERVAL: According to product labeling, the bioavailability of deferasirox was variably increased when taken with a meal.

MANAGEMENT: To ensure consistent plasma drug levels, deferasirox should be taken on an empty stomach 30 minutes before eating preferably at the same time everyday.