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8/22/2003

Atazanavir Needs Boost When Given With Tenofovir

Cheryl Thompson

Bristol-Myers Squibb Co. recently told health care providers to consider adding a small amount of ritonavir to the once-daily regimen of atazanavir and tenofovir taken by some patients with human immunodeficiency virus (HIV) infection, according to a company letter circulated yesterday by the Food and Drug Administration (FDA) MedWatch program.

Based on data from two studies, Bristol-Myers Squibb determined that patients' exposure to atazanavir, a recently available HIV protease inhibitor that the company markets as Reyataz, was markedly decreased when they took the drug with tenofovir disoproxil fumarate, a prodrug of a nucleotide analogue.

Both drugs can be taken once daily, unlike the vast majority of agents marketed as HIV treatments.

Gilead Sciences Inc. markets the tenofovir product as Viread.

In its "Dear Health Care Provider" letter, Bristol-Myers Squibb suggested using a "boosted" atazanavir regimen—that is, 100 mg of the protease inhibitor ritonavir and 300 mg, not 400 mg, of atazanavir—when the latter is taken with the tenofovir product. Information from a third study, although still under way, indicated patients who took the boosted regimen did not suffer more intense adverse events than if they had taken atazanavir 400 mg/day, the standard dosage. The company said the three studies' data are under review by FDA.

Abbott Laboratories markets ritonavir as Norvir.

The original FDA-approved labeling for atazanavir notes that patients' exposure to the drug, when taken at a dosage of 300 mg/day, increased greatly after a 100-mg daily dose of ritonavir was added.

In the June 20 approval letter for atazanavir, FDA encouraged, but did not require, Bristol-Myers Squibb to conduct a study to determine the dosage recommendation when the HIV treatment regimen includes the tenofovir product.