Coadministration has not been studied and is not recommended. Primidone is metabolised by CYP3A4 to the active metabolite phenobarbital. Phenobarbital induces CYP3A4 and is expected to significantly decrease doravirine exposure, leading to loss of therapeutic effect and possible development of resistance. Alternative anticonvulsants should be considered. At least a 4-week cessation period is recommended prior to initiation of doravirine due to the persisting inducing effect upon discontinuation of a moderate/strong inducer. Phenobarbital induces P-gp and could reduce the absorption of tenofovir-DF, however this effect likely to be small. Lamivudine does not interact with these metabolic pathways.