FDA - Safety testing of drug metabolites

This guidance provides recommendations to industry on when and how to identify and characterize drug metabolites whose nonclinical toxicity needs to be evaluated. Drug metabolites may need to be determined in nonclinical studies when they are disproportionate drug metabolites, that is, metabolites identified only in humans or present at higher plasma concentrations in humans than in any of the animal species used during standard nonclinical toxicology testing.

See: https://www.fda.gov/media/72279/download

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)