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New HIV Drug Rejected by FDA Advisory Panel

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Nov. 1, 1999 (Gaithersburg, Md.) -- An FDA Advisory Committee failed to recommend a new drug, ADV (adefovir dipivoxil), for treatment of HIV. Some were hoping the drug would be an important addition to the list of already available anti-HIV drugs. "Physicians and patients are scrambling," says Christopher Mathews, MD, committee consultant. Thousands of patients have already received ADV under a special experimental "expanded access" program.

A string of physicians and HIV patients, speaking on the drug's behalf, emphasized that the drug would be an important option for patients who fail with other therapies. Many of these patients and physicians were paid by the drug's manufacturer, Gilead Sciences, to attend the committee meeting.

In a lopsided 13-1 vote, the FDA's Antiviral Drugs Advisory Committee today moved not to recommend approval of ADV, which is a reverse transcriptase inhibitor similar to AZT (zidovudine). The company had sought to market the drug for patients who had failed other treatments for HIV.

Although the drug has shown promise, the firm had limited data for its proposed dosage. Moreover, the agent has shown troublesome kidney toxicity.

In one trial of more than 400 patients, ADV demonstrated a significant reduction in the HIV virus that lasted through 48 weeks of treatment. But the trial showed no effect on CD-4 cell count, a marker of severity of the disease, and several other trials failed to demonstrate positive results -- or lacked sufficient power for FDA to evaluate.

According to panel member, Wafaa Ed-Sadr, MD, "I don't think we're there yet."

Although the ADV studies that the company initially conducted focused on a 120 mg daily dose, liver toxicity concerns prompted Gilead to halve the proposed dose. One trial then compared the 60 mg and 120 mg doses, which were administered to patients as part of varying combination therapy. Results suggested similar outcomes, but the study lacked long-term measures of the lower doses' effectiveness and safety.

Members of the committee said they were concerned that the other medications that patients took in that trial were actually responsible for the observed effectiveness.

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