FDA questions delay approval of Human Genome Sciences anthrax drug raxibacumab

Human Genome Sciences said Monday that approval of its experimental anthrax drug hit a delay as regulators asked the firm for more information about the treatment.

The Food and Drug Administration wrote in a letter to the Rockville company that it had further questions about the drug, called raxibacumab, and would withhold approval until HGS provided additional information. HGS said that it expects to answer the questions in the next few months.

"We have responded to all of FDA's previous questions," said Sally D. Bolmer, the company's senior vice president of development and regulatory affairs, in a statement. "We plan to address the current questions as well."

While the company did not identify the agency's questions about the drug, Bolmer also referred to the hurdles involved with developing a drug for which human testing would cross ethical boundaries. Bolmer said that the agency's questions "appear to be inconsistent with the FDA's published final rule governing the development of new drugs when human efficacy studies are not ethical or feasible."

An analyst who follows the biotech sector, David S. Moskowitz of Caris & Co., said that it is common for companies to receive this sort of follow-up request from the FDA.

"It's up to the company to communicate to investors and the public how complex the remaining work is," he said. "Sometimes it's just a matter of paperwork."

The drug is designed to help patients who have already become infected with anthrax. People exposed to the disease through inhalation may not realize they have become infected until it is too late for antibiotics alone to be effective. Raxibacumab, also known as ABthrax, is designed to target anthrax toxins after they are released into the body.

Even though raxibacumab has yet to receive final FDA approval, it already is bringing in revenue for HGS, thanks to U.S. government purchases of the drug for an emergency stockpile.

Moskowitz said that it is not unusual for the government to begin to accumulate a drug with this type of use before it is approved. "It doesn't necessarily require approval to be stockpiled," he said.

In the first half of 2009, the drug brought in $162.7 million for HGS. Under the terms of its deal with the government, the company would make an additional $10 million when the drug receives FDA approval.

In April, HGS delivered 20,000 doses of raxibacumab to the U.S. Strategic National Stockpile under a federal contract. HGS received a second order in July for 45,000 doses of the drug, to be delivered over three years.