FDA Approves Raxibacumab for Inhalational Anthrax

Miriam E. Tucker


December 14, 2012

The US Food and Drug Administration (FDA) today has approved a novel drug for the treatment of inhalational anthrax.

The drug, raxibacumab, was developed by Human Genome Sciences (HGS) under a US government contract following the 2001 anthrax attacks through the US mail that killed 5 of 11 people despite antibiotic treatment. It is now a product of GlaxoSmithKline, which acquired HGS in July 2012.

In contrast to antibiotics, which eradicate the Bacillus anthracis bacterium itself, raxibacumab targets the toxins produced by B anthracis. These toxins are the cause of death in most human inhalational anthrax disease cases, including those in the 2001 attacks.

"In addition to antibiotics, raxibacumab will be a useful treatment to have available should an anthrax bioterrorism event occur," Edward Cox, MD, MPH, director of the Office of Antimicrobial Products in the FDA's Center for Drug Evaluation and Research, said in an agency press release.

"Although antibiotics are approved to prevent and treat anthrax infection, raxibacumab is the first approved agent that acts by neutralizing the toxins produced by B. anthracis," Dr. Cox said.

Raxibacumab, which is administered in a single 2-hour intravenous infusion, was already included in the Strategic National Stockpile, which also includes vaccines, antibiotics, and antitoxins targeting anthrax. Not all of these products are licensed yet.

Because naturally occurring inhalational anthrax infection in humans is rare, and studies deliberately exposing humans to the pathogen would be unethical, efficacy studies of raxibacumab were conducted in animals under the FDA's Animal Rule. Established in 2002, the rule allows companies to seek approval for the marketing of drugs or biologics based on efficacy data from animal studies, provided certain criteria are met. Safety data can be collected from humans, however, as was done with raxibacumab.

Raxibacumab, for which efficacy data were obtained from rabbits, is the first monoclonal antibody to be licensed under the Animal Rule.

The approval comes after an FDA advisory panel endorsed the drug at a hearing on November 2. The FDA's Anti-Infective Drugs Advisory Committee voted 16 to 1 (with 1 abstention) to endorse the clinical benefit of the recombinant human monoclonal antibody raxibacumab. The panel also voted unanimously, 18 to 0, in support of the product's safety.

"Intensive antibiotic treatment is effective, but sometimes insufficient in treating the toxemia associated with late-stage infection," explained Gerald R. Kovacs, PhD, director of the Division of Chemical, Biological, Radiological, and Nuclear Medical Countermeasures at the Biomedical Advanced Research and Development Authority office, a division of the US Department of Health and Human Services, during the hearing.

Moreover, antibiotics would be of limited value in the case of multidrug-resistant anthrax, he noted.

The US government views anthrax as a category A threat agent, meaning that it "poses greatest possible threat" to the public. "Anthrax spores can be readily produced in vitro, and with the right technology, even weaponized," Dr. Kovacs said.

The FDA granted raxibacumab fast track designation, priority review, and orphan product designation. "The drug demonstrated the potential to fill an unmet medical need, has the potential to provide safe and effective treatment where no satisfactory alternative therapy exists, and is intended to treat a rare disease, respectively," according to an agency press release.