FDA questions Human Genome drug

Anthrax treatment may not be better than older therapies

Human Genome Sciences's experimental anthrax treatment, studied more extensively in animals than in humans, may not be more effective than older therapies, the Food and Drug Administration said Friday.

Studies may not be sufficient to show that the drug, called raxibacumab, works better than antimicrobials, FDA staff members say in a report posted Friday on the agency's Web site. An FDA advisory panel will meet Tuesday in Silver Spring to discuss whether to approve the treatment.

Raxibacumab, also called Abthrax, would be the Rockville company's first marketed drug. Human Genome Sciences has already delivered 20,000 doses of the antibody to the U.S. Strategic National Stockpile, which accumulates treatments to protect citizens in the event of a bioterrorist attack or public health emergency. The contract was announced in 2006.

"When given in combination with antimicrobials, the efficacy of the combination was high, but the efficacy of antimicrobials alone was also high, raising the question of whether the animal model adequately reflects the findings from patients with inhalational anthrax," the FDA staff wrote in the documents.

The effectiveness of the treatment was tested on animals because of prohibitions on infecting human subjects with anthrax. About 326 healthy volunteers were given the drug in studies evaluating safety.

Human Genome shares fell 78 cents, or 3.8 percent, to close at $19.63. Before Friday, the stock surged more than ninefold in 2009 on successful trials of an experimental treatment for lupus.

The existing treatments, Johnson & Johnson antibiotic Levaquin and Bayer's Cipro, cured almost 100 percent of the animals, according to documents.

"In contrast, during the 2001 anthrax attacks, 5 of 11 people who developed inhalation anthrax died despite best available treatment," the staff said in the documents.

In both rabbit and monkey studies of anthrax, a single dose of raxibacumab combined with an antibiotic was of similar effectiveness to the antibiotic alone, the documents said.

Anthrax, an infection caused by the spore-forming bacillus anthracis, is seen more often in cows and sheep than in humans, though it can spread to farm workers when exposed to infected animals.

Most infections occur when the bacterial spore enters the skin. Anthrax infection can be contracted intestinally by eating contaminated meat, according to the Centers for Disease Control and Prevention.

A vaccine currently exists to prevent infection, though the CDC recommends it only for people who work with the germ in a laboratory, handle imported animal hides or other animal products from areas where there is a high incidence of anthrax, or are military personnel deployed to high-risk areas. Anthrax is also treated with antibiotics.

Human Genome's drug doesn't target anthrax directly. Rather, it prevents toxins generated by an anthrax infection from killing cells.

The toxins cause many of the life-threatening symptoms, according to the company.

-- Bloomberg News