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Analysis of determinants of long-term efficacy of unboosted atazanavir-based regimens in the clinical setting


Switch to unboosted atazanavir (ATV 400 mg qd), although not licensed in Europe, is an attractive off-label option due to convenience and tolerability. However there is a substantial lack of data concerning efficacy of ATV 400 mg-based regimens outside the trial setting. Our aim was to perform a retrospective study of determinants of long term efficacy in 2 Italian large HIV clinics.

Materials and methods

A retrospective analysis of virological (responder = last viral load < 50 copies/ml) and PK data of patients (pts) administered with ATV 400 mg QD + 2 N(Nt)RTIs for at least 3 months was performed. Genotypic Sensitivity Score (GSS) and ATV resistance associated mutations (RAMs) were calculated according to Stanford database using cumulative genotype. ATV Ctrough was measured by a validated HPLC method.


246 patients [65% male, mean age 47.5 years (±9), mean BMI 23.8 Kg/m2 (±3,4)] were considered. 40.7% and 6.6% were HCV- or HBV-coinfected, respectively, of whom 23 (9.3% of total) were cirrhotic. 32,9% and 17.9% of pts showed previous virological failure to NNRTIs and to PIs, respectively. Switch to ATV was mainly (48,4%) due to toxicity [dyslipidemia (21,5%) and gastrointestinal side effects (9,7%)] and to simplification (28,5%); last regimen was boosted PI-based in 178 patients (72.3%, 48% of whom ATV/r) and NNRTI-based in 24 (9.8%). At baseline CD4+ cell count was 428 cell/mm3 (±223) and 58,1% showed undetectable viral load. 212 (86.5%) patients had previous genotype available: backbone GSS was < 2 in 36,9% of patients and 6,7% had at least 1 ATV-RAM. Mean (±SD) follow-up was 120 weeks (± 64), and 235 (95.5%) pts were responders (74.4% still on treatment) while 11 (4.5%) showed a virological failure (3 showed selection of ATV-RAMs). ATV Ctrough (available in 84 patients) was higher in responders (median value 130 vs. 70 ng/ml), although this was not statistically significant (p>0.05). At multivariate analysis, GSS<2, ATV-RAMs ≥1 and self-reported non-adherence were associated with failure. ATV was stopped only in 4 patients (1.6%) for side effects.


Over a mean follow up of more than 2 years, unboosted ATV showed high efficacy with good tolerability even in a clinical cohort including moderately experienced pts. However, due to the impact of GSS of backbone and presence of ATV-RAMs on the risk of failure, pts need to be accurately selected. The role of ATV plasma exposure deserves to be clarified on a larger sample size.

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This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Bonora, S., Calcagno, A., Viganò, O. et al. Analysis of determinants of long-term efficacy of unboosted atazanavir-based regimens in the clinical setting. JIAS 13 (Suppl 4), P48 (2010).

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