Anthrax drug's effectiveness questioned

Federal regulators have questioned the effectiveness of Human Genome Sciences, Inc.'s new anthrax treatment raxibacumab.

Raxibacumab, also known as ABThrax, is a new treatment for inhaled anthrax that targets the bacteria's toxins that are released in a patient's blood and tissue.

The denial of approval comes just weeks after an FDA advisory panel questioned the effectiveness of raxibacumab compared to existing drugs. Raxibacumab was tested primarily on animals, not on humans. Because of the discrepancy in effectiveness, the panel recommended that the FDA not approve raxibacumab.

Animal testing completed by Human Genome Sciences in 2007 showed that a single raxibacumab dose improved survival rates in rabbits and monkeys by as much as 64 percent. More than 400 human volunteers were also administered raxibacumab to determine the drug's safety.

Despite the testing by Human Genome Sciences, the FDA's advisory panel questioned whether or not raxibacumab differentiated itself from Levaquin and Cipro, two readily available antibiotics already on the market.

Human Genome Sciences' executive vice president said that it was unfortunate that the questions raised by the FDA could not be resolved prior to the ruling but noted that the vaccine is still being stockpiled for use in the even of an emergency while the FDA reconsiders its stance.