Bioequivalence and Bioavailability Forum

Dear all
According to the BE guideline bioequivalence should be demonstrated on the parent molecule, i.e. desogestrel, even if the metabolite is the active substance. To my knowledge desogestrel is not stable and it is not possible to measure the parent compound. Therefore the active metabolite etonogestrel (= 3-ketodesogestrel) is measured for the PK evaluations. Am I right or is it in fact possible to measure the parent drug after dosing of two x 0.075 mg tablets?
I am looking forward to your replies.
Kind regards
Dan