Bioequivalence and Bioavailability Forum

Dear Mr John,

❝ does that mean we don't need to set the washout period to accommodate the metabolite

No. FDA Guidance for Industry, Bioavailability and Bioequivalence Studies for Orally Administered Drug Products — General Considerations states that "An adequate washout period (e.g., more than 5 half lives of the moieties to be measured) would separate each treatment.
Since, the metabolite is also one of the moiety you plan to measure, washout period should be calculated based to half lives of both metabolite and parent compound.

❝ Example: Half-life for parent is 6 hours and for metabolite is 20 hours. Use of 7 day washout can lead to pre-dose/carryover concentration for the metabolite.

In my personal opinion, a wash out period of 7 days will be sufficient since FDA recommends more than 5 half lives as wash out period (5*20=100 >4.17 days)