FDA reviewers: raxibacumab has 'clinically meaningful benefit'

FDA reviewers said raxibacumab from Human Genome Sciences Inc. has a "positive" benefit-risk profile for treating inhalational anthrax. The human mAb against Bacillus anthracis protective antigen was developed under the FDA Animal Rule, which allows for marketing approval to be granted based on efficacy in relevant animal models and an acceptable safety risk profile in humans. The reviewers noted that in pivotal studies in rabbits and macaques, raxibacumab provided a "significant survival benefit" over placebo in animals with systemic anthrax disease, the primary endpoint. The reviewers said that combination studies of raxibacumab with antibiotics were also "positive" on the primary endpoint of survival compared with placebo and showed that concomitant treatment with raxibacumab does not alter the efficacy or pharmacokinetics of the antibiotics. Additionally, when raxibacumab was administered concomitantly with antibiotics late in the course of disease, the combination treatment had a mortality rate that was "nearly half that of antibiotics alone."

The reviewers also said raxibacumab's safety "has been demonstrated in healthy adults," noting that in a study of 326 healthy volunteers there were three serious adverse events, none of which were likely to be related to raxibacumab. The reviewers concluded that there is a "demonstrated increase in survival" with raxibacumab alone or in combination with antimicrobials, regardless of when the products are given during the course of an anthrax infection. The comments came in briefing documents released ahead of Friday's meeting of the Anti-Infective Drugs Advisory Committee to discuss a resubmitted BLA for raxibacumab. ...