Drug Interaction Report

GENERALLY AVOID: Coadministration with inducers of uridine diphosphate glucuronosyltransferase (UGT) may decrease the plasma concentrations of deferasirox, which is primarily metabolized by UGT1A1- and UGT1A3-mediated glucuronidation. In healthy volunteers, administration of a single 30 mg/kg dose of deferasirox with the potent UGT inducer rifampin (600 mg/day for 9 days) resulted in a reduction of deferasirox systemic exposure (AUC) by 44%. The effect of other UGT inducers on the pharmacokinetics of deferasirox is unknown.

MANAGEMENT: The concomitant use of deferasirox with potent UGT inducers such as rifampin, phenytoin, phenobarbital, carbamazepine, and ritonavir should generally be avoided. Otherwise, consideration may be given to increasing the initial dosage of deferasirox by 50% during coadministration with potent UGT inducers, with subsequent adjustments made according to serum ferritin levels and clinical response.

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as well as clinical and laboratory monitoring may be appropriate for some drugs whenever deferasirox is added to or withdrawn from therapy.

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ADJUST DOSING INTERVAL: Administration with food may modestly affect the bioavailability of ritonavir from the various available formulations. When the oral solution was given under nonfasting conditions, peak ritonavir concentrations decreased 23% and the extent of absorption decreased 7% relative to fasting conditions. Dilution of the oral solution (within one hour of dosing) with 240 mL of chocolate milk or a nutritional supplement (Advera or Ensure) did not significantly affect the extent and rate of ritonavir absorption. When a single 100 mg dose of the tablet was administered with a high-fat meal (907 kcal; 52% fat, 15% protein, 33% carbohydrates), approximately 20% decreases in mean peak concentration (Cmax) and systemic exposure (AUC) were observed relative to administration after fasting. Similar decreases in Cmax and AUC were reported when the tablet was administered with a moderate-fat meal. In contrast, the extent of absorption of ritonavir from the soft gelatin capsule formulation was 13% higher when administered with a meal (615 KCal; 14.5% fat, 9% protein, and 76% carbohydrate) relative to fasting.

MANAGEMENT: Ritonavir should be taken with meals to enhance gastrointestinal tolerability.

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ADJUST DOSING INTERVAL: Food significantly increases the bioavailability of lopinavir from the oral solution formulation of lopinavir-ritonavir. Relative to fasting, administration of lopinavir-ritonavir oral solution with a moderate-fat meal (500 to 682 Kcal; 23% to 25% calories from fat) increased lopinavir peak plasma concentration (Cmax) and systemic exposure (AUC) by 54% and 80%, respectively, whereas administration with a high-fat meal (872 Kcal; 56% from fat) increased lopinavir Cmax and AUC by 56% and 130%, respectively. No clinically significant changes in Cmax and AUC were observed following administration of lopinavir-ritonavir tablets under fed conditions versus fasted conditions. Relative to fasting, administration of a single 400 mg-100 mg dose (two 200 mg-50 mg tablets) with a moderate-fat meal (558 Kcal; 24.1% calories from fat) increased lopinavir Cmax and AUC by 17.6% and 26.9%, respectively, while administration with a high-fat meal (998 Kcal; 51.3% from fat) increased lopinavir AUC by 18.9% but not Cmax. Relative to fasting, ritonavir Cmax and AUC also increased by 4.9% and 14.9%, respectively, with the moderate-fat meal and 10.3% and 23.9%, respectively, with the high-fat meal.

MANAGEMENT: Lopinavir-ritonavir oral solution should be taken with meals to enhance bioavailability and minimize pharmacokinetic variability. Lopinavir-ritonavir tablets may be taken without regard to meals.

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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.

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