Ketoconazole is a strong inhibitor of CYP3A4 and was shown to increase doravirine exposure by ~3-fold. No dose adjustment of doravirine is required as phase I trials showed a good tolerability of doravirine with up to a 3-4 fold increase in exposure. Lamivudine does not interact with ketoconazole. However, tenofovir-DF is a substrate of P-gp and inhibitors of P-gp such as ketoconazole could potentially increase the absorption of tenofovir-DF, thereby increasing the systemic concentration of tenofovir. Monitoring of tenofovir-associated adverse reactions, including frequent renal monitoring, is recommended.