After approving a completely novel product using the animal rule for the first time, the U.S. Food and Drug Administration may have presented more questions than answers.
On December 14, the FDA used the animal rule for the first time in a decade to approve raxibacumab, an antibody drug used for the treatment or prevention of respiratory anthrax. Since the animal rule's introduction in 2002 to approve medical countermeasures to chemical, biological and radiological weapons based on animal studies alone, no drugs had ever been approved without prior FDA approval for other afflictions or approval in other countries, Nature Medicine
"It's really the first drug that has been approved using the animal rule as the sole mechanism," James Swearengen, the director of comparative medicine at the National Biodefense Analysis and Countermeasures Center at Fort Detrick, said, according to Nature Medicine
. "It's a milestone."
Swearengen said that the delay in putting the animal rule to the test was the result of a learning curve.
The rule originally stated that the FDA would accept animal efficacy data if it represented a sufficiently well-characterized animal model for predicting the response in humans. Scientists had a difficult time finding such an ideal model to justify using the rule.
In 2011, a committee with the National Academy of Sciences recommended adopting a model of compartmentalization that would use efficacy data gleaned from components of an animal rather than relying on information obtained from whole organisms.
The FDA will release an updated version of its draft guidance on the animal rule later this year that was first published in January 2009. The document could help to facilitate the development of medical countermeasures by clarifying the approval path, Nature Medicine
Travis Warren, a research scientist at Fort Detrick, said that there is tremendous confusion about the rule and more guidance is needed. Other experts said that more drugs would be in the pipeline if the animal rule was made to be completely clear.