Pharmacokinetics, protein-binding-adjusted inhibitory quotients for atazanavir/ritonavir 300/100-mg in treatment-naïve 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-naïve patients.Methods: Protein-binding-adjusted IQs were calculated in 100 treatment-naïve 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.