FDA to discuss experimental drug's effectiveness against anthrax

A Human Genome Sciences Inc. drug worked better than a placebo but similar to antibiotics for treating anthrax exposure in animal studies, U.S. drug reviewers said in a summary released Oct. 23.

The rabbit and monkey studies of the experimental drug, ABthrax or raxibacumab, had limitations and "it is still unknown how well these models and results predict efficacy in humans," the Food and Drug Administration staff said.

The FDA will ask an advisory panel that meets Oct. 27 if the drug's benefits outweigh risks for treating potentially deadly infections caused from inhaling anthrax, a bacterium feared as a possible biological weapon. FDA rules allow companies to study two animals in lieu of people to show effectiveness for some dangerous infections.

Adding a single intravenous dose of ABthrax to antibiotics produced similar effectiveness to antibiotics alone, FDA staff said. The advisory panel will be asked if the drug might interfere with antibiotics, or if more data is needed to show ABthrax provided any benefit. Antibiotics in the studies successfully treated between 95 percent and 100 percent of the animals, an unexpectedly high rate, the agency reviewers said.

"Given the high efficacy of the [antibiotic] arms" in the rabbit and monkey studies, "the added benefit of raxibacumab ... could not be determined," FDA staff said.

In a separate summary prepared for the advisory panel, Human Genome said antibiotics alone could cure all anthrax infections in tests but "the 2001 attacks and other real-world experiences have demonstrated that antibiotics alone are not 100 percent effective" and new options were needed. If inhaled, anthrax can take hold quickly and by the time symptoms start showing it is often too late for successful treatment with antibiotics.