Potential associations between atazanavir exposure and clinical outcome: A pharmacokinetic sub-study from the MODAt randomized trial

The 96-week results of the Monotherapy Once a Day with Atazanavir/r (MODAt) study [NCT01511809] showed an inferior virological efficacy of atazanavir (ATV)/ritonavir monotherapy versus triple therapy, which was promptly retrieved by the reintroduction of nucleoside/nucleotide inhibitors of reverse transcriptase [N(n)RTIs]. We aimed to identify potential relationships between ATV exposure and clinical outcome in HIV-1 subjects treated with ATV/ritonavir monotherapy [ATV/r 300/100 mg] versus ATV/ritonavir triple therapy [ATV/r 300/100 mg+2NRTIs]. A chromatographic method coupled with tandem mass spectrometry was applied to analyze ATV plasma concentrations in a pharmacokinetic sub-study from the MODAt trial. Mixed linear models were used to examine the ATV plasma concentration trend during follow-up and to assess the association between ATV plasma concentrations trajectories with the study arm or the occurrence of treatment failure or drugrelated adverse events or the grading of baseline total bilirubin (<3 vs >=3). The analyses were performed using SAS Software, release 9.4 (SAS Institute, Cary, NC, USA). Overall, ATV plasma Ctrough concentration did not vary during follow-up (slope: +0.75 ng/mL/week, 95%CI: -0.97 to 2.47, p=0.387); trajectories did not differ between study arms (p=0.527). The unadjusted model-based means (95%CI) of ATV Ctrough during follow-up were 835 (95%CI: 657-1012) ng/ml in the ATV/r monotherapy arm as compared to 911 (95%CI: 740-1082) ng/mL in the ATV/r triple therapy arm (p=0.621). Mean ATV Ctrough was similar in subjects with or without adverse events (AEs). Subjects treated with ATV/r monotherapy showed significantly higher ATV concentrations as compared to subjects without adverse events or treated with ATV/r triple therapy. ATV concentrations were associated with the grading of baseline total bilirubin and the occurrence of drug-related AEs but not with HCV infection. Our findings showed a lack of association between ATV concentrations and treatment failure both in ATV/r monotherapy and triple therapy. Conversely, these data emphasized that ATV concentrations are associated with the development of side-effects in both subjects treated with ATV/r monotherapy and subjects treated with ATV/r triple therapy.