Coadministration is contraindicated in product labels for Biktarvy (bictegravir, emtricitabine, tenofovir alafenamide). Coadministration of rifampicin (600 mg once daily) and bictegravir alone (75 mg single dose) decreased bictegravir Cmax and AUC by 28% and 75%. In the INSIGHT study, coadministration of rifampicin (600 mg once daily) and twice daily bictegravir/emtricitabine/tenofovir (50/200/25 mg, twice daily) decreased bictegravir AUC, Cmax and Ctrough by approximately 62%, 53% and 78%, respectively, and a PK substudy showed intracellular tenofovir-DP concentrations to be similar to those with once-daily TAF alone. Despite an ~80% reduction in bictegravir trough concentrations, average trough concentrations remained 3.1-fold above the protein adjusted 95% effective trough concentration (inhibitory quotient, 0.162 mg/L). None of the Ctrough values following directly observed dosing were below the inhibitory quotient . At week 48, HIV VL was <50 copies/mL in 76/80 (95%) participants. There were no treatment discontinuations or drug switches due to adverse events. These data suggest that twice daily Biktarvy with rifampicin could be considered in some individuals with no previous treatment failure or factors that could further reduce bictegravir exposure (i.e., overweight/obesity, mineral supplements).

Coadministration has not been studied but based on metabolism and clearance a clinically significant interaction is unlikely. Adalimumab is a monoclonal IgG antibody. Elimination is similar to endogenous IgG and occurs primarily via proteolytic catabolism throughout the body.

Coadministration has not been studied but based on metabolism and clearance, a clinically significant interaction is unlikely. Although in vitro data suggest that some harma alkaloids found in ayahuasca preparations have a weak/moderate inhibitory effect on CYP3A4, this is unlikely to impact the exposure of bictegravir as it is metabolized equally by CYP3A4 and UGT1A1. No effect on emtricitabine or tenofovir alafenamide is expected.

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 (inactive metabolite). Bictegravir does not inhibit or induce P450 enzymes; emtricitabine and tenofovir alafenamide do not interact with letrozole’s metabolic pathway.