Pharmacokinetics, protein-binding-adjusted inhibitory quotients for atazanavir/ritonavir 300/100 mg in treatment-naive HIV-infected patients

Objectives Studies have shown the importance of having a high protein-binding-adjusted inhibitory quotient (IQ) for protease inhibitors (PIs) boosted with ritonavir. The objective of this study was to explore the virological response when combination atazanavir/ritonavir was administered to treatment-naive patients. Methods Protein-binding-adjusted IQs were calculated in 100 treatment-naive patients initiating therapy with atazanavir 300 mg/ritonavir 100 mg plus two nucleoside reverse transcriptase inhibitors. Results The median atazanavir trough level was 635 ng/mL [interquartile range (IQR) 342-1000] and the median atazanavir protein-binding-adjusted IQ was 45 (IQR 24-71). Eighty-four per cent of patients had a successful virological response, and those who failed did not develop resistance. The IQ for boosted atazanavir is high, resulting in rare treatment failure without resistance mutations. Conclusions This study showed that the protein-binding-adjusted IQ of atazanavir is close to those measured for lopinavir and darunavir used once daily in first-line treatment. Finally the selection of resistance in the case of virological failure (plasma viral load > 400 HIV-1 RNA copies/mL) to atazanavir/ritonavir used in first-line therapy seems uncommon, as it is for all boosted PIs.