Drug Interaction Report

Coadministration with osimertinib may alter the plasma concentrations of drugs that are primarily metabolized by CYP450 3A4. In vitro, osimertinib has been shown to be a competitive inhibitor as well as inducer of CYP450 3A4. However, a clinically significant inhibitory effect on CYP450 3A4 has not been demonstrated in clinical drug interaction studies. In a pharmacokinetic study of 49 patients with non-small cell lung cancer, coadministration of osimertinib with the sensitive CYP450 3A4 substrate simvastatin decreased the area under the concentration-time curve (AUC) and peak plasma concentration (Cmax) of simvastatin by approximately 9% and 23%, respectively. These reductions are also not considered clinically significant. Based on these observations, osimertinib may be administered with CYP450 3A4 substrates without the need for increased clinical monitoring.

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.