Abstract: Ritonavir-boosted atazanavir is a victim of drug–drug interaction with rifampicin, a key component of antitubercular treatment. In a recent dose escalation clinical trial, we showed that increasing atazanavir/ritonavir to 300/100mg b.i.d. compensates for reduced drug exposure in plasma due to rifampicin, but the intracellular effects remained unexplored. This sub-study investigated the intracellular penetration of atazanavir/ritonavir and dolutegravir into peripheral blood mononuclear cells (PBMC). Twenty-six healthy volunteers living with HIV, virologically suppressed, and taking atazanavir/ritonavir containing regimens were enrolled. The trial consisted of four sequential periods: PK1, participants were on atazanavir/ritonavir 300/100mg q.d.; at PK2, rifampicin 600mg q.d. and dolutegravir 50mg b.i.d. were added (2weeks); at PK3, atazanavir/ritonavir dose was increased to 300/100mg b.i.d. (1week); at PK4, rifampicin dose was doubled (1week). Atazanavir, ritonavir, and dolutegravir were quantified in plasma and PBMC using LC–MS/MS methods to evaluate steady-state concentrations at the end of each period. Atazanavir/ ritonavir dose escalation successfully restored intracellular concentrations comparable to those observed without rifampicin, with a geometric mean ratio of 0.99 (CI90 0.72–1.41) for atazanavir at PK3 compared with PK1. The intracellular concentration of dolutegravir increased significantly with atazanavir/ritonavir dose escalation, similar to plasma. Finally, further, increasing the rifampicin dose did not show an additional impact on atazanavir/ ritonavir concentrations in PBMC. The study confirms that increasing the ATV/r dose can be an effective strategy for compensating rifampicin effects even at the intracellular level, supporting its use in clinical settings.
