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as well as clinical and laboratory monitoring may be appropriate for some drugs whenever deferasirox is added to or withdrawn from therapy.

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.

Grapefruit juice may delay the gastrointestinal absorption of clarithromycin but does not appear to affect the overall extent of absorption or inhibit the metabolism of clarithromycin. The mechanism of interaction is unknown but may be related to competition for intestinal CYP450 3A4 and/or absorptive sites. In an open-label, randomized, crossover study consisting of 12 healthy subjects, coadministration with grapefruit juice increased the time to reach peak plasma concentration (Tmax) of both clarithromycin and 14-hydroxyclarithromycin (the active metabolite) by 80% and 104%, respectively, compared to water. Other pharmacokinetic parameters were not significantly altered. This interaction is unlikely to be of clinical significance.