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Home > Treatment > HIV Meds Quarterly > Spring 2008 > Efficacy
Efficacy: Atazanavir/Ritonavir vs Lopinavir/Ritonavir

Clinicians often prefer ritonavir-boosted atazanavir (ATV/r) to unboosted ATV for use in initial therapy, and this strategy is recommended by the adult and adolescent treatment guidelines of the U.S. Department of Health and Human Services. Data to support this practice have been scanty, however, and ATV/r has not been adequately compared with standard-of-care protease inhibitor-boosted regimens for treatment-naive individuals. The results of a study presented at the 15th Conference on Retroviruses and Opportunistic Infections in February 2008 provide solid evidence of the efficacy and tolerability of ATV/r in initial therapy.

CASTLE, a large (883 subjects) randomized, open-label noninferiority study, compared ATV/r with lopinavir/ritonavir (Kaletra, LPV/r) in antiretroviral-naive patients. The two treatment groups were well matched at baseline; the median HIV RNA viral load was 5 log10 copies/mL and the median CD4 count was just above 200 cells/µL. Each protease inhibitor was given in combination with tenofovir + emtricitabine (Truvada); the LPV/r was given twice daily, in the soft-gel formulation. At 48 weeks, the proportion of patients in the two groups with HIV RNA <50 copies/mL was not significantly different: 78% in the ATV arm and 76% in the LPV arm. ATV/r performed as well as LPV/r in patients with baseline HIV RNA >100,000 copies/mL as well as in those with lower baseline viral loads. The increase in CD4 count in the two groups was similar: 203 cells/µL for the ATV arm, and 219 cells/µL for the LPV arm. Increases in fasting cholesterol and triglyceride levels were seen more frequently in LPV/r recipients, as were nausea and diarrhea; hyperbilirubinemia was seen more frequently in ATV/r recipients.


  1. Molina J-M, Andrade-Villanueva J, Echevarria J, et al. Efficacy and safety of once-daily atazanavir/ritonavir compared to twice-daily lopinavir/ritonavir, each in combination with tenofovir and emtricitabine ARV-naive HIV-1-infected subjects: The CASTLE study, 48-week results. In: Program and abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; February 3-6, 2008; Boston. Abstract 37.
  2. U.S. Department of Health and Human Services. Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents. January 29, 2008. Available online at Accessed February 28, 2008.