Clinical pharmacokinetics and summary of efficacy and tolerability of atazanavir

Abstract

The efficacy of HIV-1 protease inhibitors (PIs) as part of highly active antiretroviral therapy is now well established and has provided benefits to many patients with HIV infection. Atazanavir is a new azapeptide PI compound that was recently approved in the US and Europe. Atazanavir is recommended in combination with other antiretroviral agents for the treatment of HIV-1 infection. Atazanavir is rapidly absorbed and administration of a single dose of atazanavir with a light meal resulted in a 70% increase in area under the plasma concentration-time curve (AUC); therefore atazanavir should be taken with food. Atazanavir is 86% bound to human serum protein independently of concentration. Concentration in body fluids appeared to be lower than plasma concentration. Like other PIs, atazanavir is extensively metabolised by hepatic cytochrome P450 (CYP) 3A isoenzymes. The mean terminal elimination half-life in healthy volunteers was approximately 7 hours at steady state following administration of atazanavir 400 mg daily with a light meal. When atazanavir 300 mg was coadministered with ritonavir 100 mg on a once-daily dosage regimen, atazanavir AUC from 0 to 24 hours and minimum plasma concentration were increased by 3- to 4-fold and approximately 10-fold, respectively, compared with atazanavir 300 mg alone. Therefore, ritonavir boosted atazanavir regimen (ritonavir 100 mg and atazanavir 300 mg once daily) is increasingly favoured in some patients. Efavirenz, a potent CYP3A inducer, decreased atazanavir concentrations by 75% and, unexpectedly, tenofovir, a nucleotide reverse transcriptase inhibitor, decreased atazanavir concentrations by 25%. Average predose concentrations in HIV-infected patients who received atazanavir 400mg once daily were 273 ng/mL, which was believed to be several-fold higher than protein-binding corrected 50% inhibitory concentration of wild-type viruses. In HIV-infected patients who received once-daily ritonavir (100mg) boosted atazanavir (300 mg), mean (+/-SD) trough concentration was 862 (+/-838) ng/mL. Several clinical trials showed the efficacy of atazanavir 400 mg once daily with a nucleoside analogue backbone in antiretroviral-naive patients. The atazanavir 300/ritonavir 100 mg once-daily combination coadministered with other antiretrovirals showed the efficacy of this strategy in patients receiving efavirenz or in moderately antiretroviral-experienced HIV-infected patients. Recommended once-daily doses of atazanavir taken with food are either 400 mg or 300 mg in combination with low dose ritonavir (100 mg) in moderately antiretroviral-experienced patients. Major advantages of atazanavir to date are its simplicity of administration (once-daily administration) and its less undesirable effect on the lipid profiles in patients.