Drug Interaction Report

GENERALLY AVOID: Coadministration with grapefruit juice may slightly increase the oral bioavailability and delay the onset of action of sildenafil. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In a randomized, crossover study with 24 healthy male volunteers, ingestion of 250 mL of grapefruit juice one hour before and concurrently with a 50 mg dose of sildenafil increased the mean area under the plasma concentration-time curve (AUC) of sildenafil and its pharmacologically active N-desmethyl metabolite by 23% and 24%, respectively, compared to water. Peak plasma concentrations (Cmax) were unaltered, but the time to reach sildenafil Cmax was prolonged by 0.25 hour. The observed increase in sildenafil bioavailability is unlikely to be of clinical significance in most individuals. However, pharmacokinetic interactions involving grapefruit juice are often subject to a high degree of interpatient variability and may be significant in the occasional susceptible patient. Indeed, one subject in the study had a 2.6-fold increase in sildenafil concentrations.

MANAGEMENT: It may be advisable to avoid administration of sildenafil with grapefruit juice to prevent potential toxicity and delay in onset of action.

ADJUST DOSING INTERVAL: Food may alter the oral bioavailability of cabozantinib. When healthy subjects were given a single 140 mg oral dose with a high-fat meal, cabozantinib peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 41% and 57%, respectively, relative to administration under fasting conditions. In clinical studies, patients were administered cabozantinib without food.

GENERALLY AVOID: Coadministration with grapefruit juice is likely to increase the plasma concentrations of cabozantinib, which is primarily metabolized by CYP450 3A4. However, the interaction has not been studied. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit.

MANAGEMENT: Cabozantinib should be administered at least one hour before or two hours after a meal. The consumption of grapefruit, grapefruit juice, and supplements that contain grapefruit extract should be avoided.