PR Newswire - December 6, 1995

Pronounced antiviral activity and immunologic benefits were maintained in HIV infected individuals after 32 weeks of treatment with the experimental compound ritonavir at the highest dose level studied, according to a multi-national study published in the Dec. 7 issue of The New England Journal of Medicine.

"The viral load decrease and the CD4 cell increase are stronger than that observed during treatment with reverse transcriptase inhibitors such as AZT, ddI, ddC, or 3TC," said Professor Sven A. Danner, M.D., investigator for the study, head of the Clinical AIDS Unit, Academic Medical Center, University of Amsterdam and the article's principal author.

The double-blind, placebo-controlled study, conducted in The Netherlands, Spain and Australia, compared four dose regimens in 84 patients. Patients were randomized to receive ritonavir at doses of 300 mg, 400 mg, 500 mg, or 600 mg twice daily, or matching placebo. The study consisted of a four-week placebo-controlled phase followed by a maintenance period in which all individuals received continued ritonavir therapy.

A total of 76 of the 84 patients enrolled continued through the initial four-week placebo-controlled phase to receive drug in the maintenance phase of the study. Mean decreases in the number of viral particles in the blood (so-called viral load) after four weeks of ritonavir therapy were 80 percent, 85 percent, 89 percent and 93 percent from baseline, respectively, for the 300 mg, 400 mg, 500 mg and 600 mg regimens. While viral load approached baseline levels after 16 weeks of treatment at the 300 mg and 400 mg dose levels and viral load began to rebound after 24 weeks of treatment at 500 mg, reductions in viral load were sustained in patients on the 600 mg regimen.

Similarly, initial increases from baseline in median CD4 lymphocyte counts were observed at all dose levels. In the 300 mg and 400 mg groups, CD4 counts approached baseline levels after 24 weeks of treatment. The 600 mg regimen, however, produced the largest and most sustained median CD4 count increase -- 230 cells per microliter at 32 weeks of treatment.

The most common side effects observed in patients in the study were nausea, perioral paresthesia, and elevated hepatic transaminase and triglyceride levels.

"The effects of monotherapy with ritonavir as seen in this study even outweight the virological and immunological effects observed during treatment with combinations of two reverse transcriptase inhibitors," said Professor Danner. "Therefore, combinations of anti-HIV compounds including ritonavir should be tested in clinical trials. Such studies already are in progress."

Ritonavir is in clinical development at Abbott Laboratories (NYSE: ABT) for the treatment of HIV-1 infection.

CONTACT: Sarah Coady of Bozell Public Relations, 312-988-2347/ 15:57 EST

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