Metabolite , generally safety testing

In general, safety evaluation is primarily based on the toxicological testing of the parent drug. However, consumers of edible animal products are also exposed to many other products of drug metabolism, including free metabolites of... 

Generally, any parent compound and its major metabolite(s) that achieve, or are expected to achieve systemic exposure in humans should be evaluated in safety pharmacology studies. Evaluation of major metabolites is often accomplished through studies of the parent compound in animals. Additionally, if metabolites from humans are known to substantially contribute to the pharmacological actions of the therapeutic agent, it may be important to test such active metabolites. 

---