This single-center prospective study evaluated study-state pharmacokinetics of nine treatment-experienced patients receiving bictegravir/emtricitabine/tenofovir alafenamide plus darunavir/cobicistat as part of routine clinical care at a large, academic HIV clinic. Participants (mean age 59) had been on this combination for at least one month (median duration 16 months), with self-reported study drug adherence. All had creatinine clearance > 30 mL/min and viral load < 200 copies/mL (three participants had CrCl 30-59 mL/min, and five had an undetectable VL). Bictegravir, tenofovir (TFV), TAF, and darunavir profiles were examined pre-dose and then at 0.5hr, 1hr, 2hrs, and 4hrs post-dose. Compared to previously reported PK data, BIC AUC_0-tau and C_max were 26% and 12% higher than BIC/FTC/TAF alone, respectively, while TAF AUC_0-tau and C_max were 165% and 128% higher, respectively. Plasma TFV was modestly higher than historical PK data. Darunavir AUC_0-tau was increased by ~20% with a similar C_max compared to historical data on patients receiving DRV/cobicistat without BIC/FTC/TAF. No adverse events were reported, and no treatment-emergent clinical laboratory abnormalities were observed. All participants maintained viral load < 200 copies/mL. Investigators concluded that, despite modestly higher bictegravir exposure and substantially increased TAF exposure (and modest plasma TFV elevation), co-use of BIC/FTC/TAF plus DRV/cobicistat appeared safe and well-tolerated, suggesting it is a viable option for some PWH.