Coadministration has not been studied but based on metabolism and clearance a clinically significant interaction is not anticipated and contraceptive efficacy is unlikely to be affected. Ethinylestradiol is mainly metabolized by hydroxylation with CYP3A4 and CYP2C9. Desogestrel is a prodrug that requires activation to etonogestrel by CYP2C9 (and possibly CYP2C19); the metabolism of etonogestrel is mediated by CYP3A4. Sofosbuvir does not affect CYP enzymes. Sofosbuvir is a prodrug and formation of its active metabolite is unlikely to be affected by comedications. Coadministration of sofosbuvir and an oral contraceptive containing ethinylestradiol and another progestogen, norgestimate was studied. There were no clinically relevant changes in the concentrations of ethinylestradiol, norelgestromin or norgestrel.