GlaxoSmithKline's anthrax treatment raxibacumab has been given the green light by regulators in the USA.

The US Food and Drug Administration has approved raxibacumab for the treatment of  patients with inhalational anthrax due to Bacillus anthracis in combination with appropriate antibacterials and when alternative therapies are not available/appropriate. Raxibacumab is the first monoclonal antibody approved under the agency’s Animal Efficacy Rule, which allows findings from "adequate and well-controlled animal studies to support FDA approval when it is not feasible or ethical to conduct trials in humans".

The drug's effectiveness was demonstrated in one study in monkeys and three trials in rabbits. 64% of animals in the monkey study and 44% in one rabbit trial receiving the 40mg per kg dose of raxibacumab survived exposure to anthrax, compared with none in the placebo groups. All surviving animals developed toxin-neutralising antibodies.

Another study in rabbits showed that 82% of animals treated with antibiotics and raxibacumab survived exposure to anthrax compared with 65% receiving antibiotic treatment alone. The drug's safety was evaluated in 326 healthy human volunteers and common side effects included rash, extremity pain, itching and drowsiness.

Edward Cox, director of the Office of Antimicrobial Products in the FDA’s Center for Drug Evaluation and Research, said “in addition to antibiotics, raxibacumab will be a useful treatment to have available should an anthrax bioterrorism event occur". He added that although antibiotics are approved to prevent and treat anthrax infection, raxibacumab is the first agent that acts by neutralising the toxins produced by B. anthracis.

Zhi Hong, head of infectious diseases at GSK, said raxibacumab is an important part of an ongoing collaboration between the firm and the US government "to address a range of public health concerns", adding that "it will be an important addition to the new approaches required to address our critical biodefence needs".

Human Genome Sciences, recently acquired by GSK, began work on raxibacumab in 2001 in response to the anthrax attacks in the USA but the drug was rejected by the FDA in November 2009, asking for more data that the drug worked better than antibiotics alone. HGS filed the additional information in July this year.