Coadministration has not been studied but based on metabolism and clearance a clinically significant interaction is unlikely. Letrozole is metabolised by CYP3A4 and CYP2A6 to carbinol, an inactive metabolite. Doravirine does not inhibit or induce CYP enzymes. Lamivudine and tenofovir-DF do not interact with letrozole’s metabolic pathway.