Use with efavirenz is not recommended. Co-administration of efavirenz (600 mg daily) with doravirine (100 mg single dose, given the first day following the cessation of efavirenz) was studied in 17 subjects. Doravirine AUC, Cmax and C24 decreased by 62%, 35% and 85% respectively. Fourteen days following the cessation of efavirenz, doravirine AUC, Cmax and C24 were decreased by 32%, 14% and 50%, respectively.

No studies have been performed with efavirenz in combination with other NNRTIs. Since use of two NNRTIs proved not beneficial in terms of efficacy and safety, coadministration of efavirenz and another NNRTI is not recommended.

Combining two NNRTIs has not been shown to be beneficial. Efavirenz should not be coadministered with other NNRTIs.

The effect of switching from efavirenz (600 mg once daily for 14 days) to doravirine (100 mg, once daily, for 14 days) was studied in 17 healthy subjects. There was no wash-out period between the two drug regimens. Doravirine AUC, Cmax and C24 were decreased by 62%, 35% and 85% respectively, one day after switching. These decreases recovered to 32%, 14%, and 50% for AUC, Cmax, and C24, respectively, by day 14 after efavirenz cessation. Doravirine C24 reached projected therapeutic trough concentrations, based on in vitro efficacy, on day 2 following efavirenz cessation. Efavirenz was present at therapeutic concentrations (>1,000 ng/ml) until day 4 following cessation. The authors conclude that it is safe to switch from efavirenz to doravirine, as at all times drug concentrations were above the minimum required for an antiviral effect.