Atazanavir (Reyataz) is an effective antiretroviral agent with comparable efficacy to other protease inhibitors and to non-nucleoside reverse transcriptase inhibitors (NNRTIs). It must be given in combination with other antiretroviral drugs.

Several studies have tested the effectiveness of atazanavir in previously untreated patients. For example, a large international study compared atazanavir and efavirenz (Sustiva), both with AZT (zidovudine, Retrovir) and 3TC (lamivudine, Epivir) among 805 people who had not previously taken antiretroviral therapy. After 48 weeks, 70% of the atazanavir group and 64% of the efavirenz group had viral load below 400 copies/ml by intent-to-treat analysis, but only 32% and 37% of atazanavir and efavirenz recipients, respectively, had viral load below 50 copies/ml. Mean CD4 cell count increases were similar in the atazanavir and efavirenz arms^[1]. More recent data have shown that atazanavir is of similar effectiveness and safety when it is dosed with or without low-dose ritonavir (Norvir) to boost atazanavir levels^[2].

The AI424-008 study has shown that atazanavir is of similar efficacy to the protease inhibitor nelfinavir (Viracept) in patients who have not taken antiretroviral therapy. After 48 weeks, similar numbers of patients had undetectable viral loads, with similar CD4 cell count increases^[3]. The A1424-007 study came to similar conclusions^[4].

Data on atazanavir in treatment-experienced patients are also available. Unsurprisingly, study A1424-043 showed that atazanavir as a single protease inhibitor is not as potent as ritonavir-boosted lopinavir (Kaletra)^[5]. However, study A1424-045 showed that ritonavir-boosted atazanavir does seem to be comparable to Kaletra in treatment-experienced people in terms of suppressing HIV levels and allowing CD4 cell counts to rise. After 96 weeks, 33% of the lopinavir group and 30% of the atazanavir group had viral load below 50 copies/ml, in spite of all patients taking tenofovir (Viread), which reduces atazanavir concentrations. However, more patients in the Kaletra arm experienced severe gastrointestinal side-effects, such as diarrhoea^[6]. The relative effects of the drugs in this study were unaffected by the number of baseline mutations^[7].

There is also evidence that dual boosted protease inhibitor drug combinations including atazanavir with Kaletra, ritonavir-boosted saquinavir (Invirase) are effective and safe in patients with substantial treatment experience^[8][9].

Recent evidence has suggested that ritonavir-boosted atazanavir-based treatment combinations are safe and well tolerated in patients infected with hepatitis B or hepatitis C viruses. Similar rates of liver enzyme elevations were seen in a group of 180 hepatitis-co-infected patients and 124 patients who were not co-infected, with similar withdrawal rates in the two groups^[10].

Ritonavir-boosted atazanavir with no other anti-HIV drugs may also be a suitable 'maintenance' treatment for patients who have suppressed viral loads on combination therapy. One study of 36 patients found that 31 maintained viral suppression for at least 24 weeks^[11]. However, larger, randomised studies are required before this strategy can be recommended.