For Valentine’s Day, FDA issued a new guidance on metabolite safety testing. Essentially, it outlines the non-clinical testing that may be required when the metabolism in humans produces significantly higher amounts of the same metabolites in the animal species where the toxicology was assessed.
As the guidance points out, recent advances in analytical technology have revealed instances where the tox data are potentially not indicative of the exposure in humans.
The impact on 505(b)(2) development plans is that in the interval since the approval of the RLD, metabolites may have been identified. These new or found-to-be-higher metabolites may need animal testing or, at least, justification why such testing is not needed