Bioequivalence and Bioavailability Forum

Hi Mutasim & all,

yesterday at BioBridges Paola Coppola (MHRA, PKWP observer) presented the state of affairs. The ezetimibe guidance is finalized and will be published soon. No changes to the draft. You are right and I was wrong. One should indeed measure both ezetimibe and its glucuronide. BE should be based on their sum* only.

I still think that’s stupid. Both methods have errors (inaccurate, imprecise). If you evaluate the sum of concentrations, errors will sum up as well. Given, the concentrations of the glucuronide are two orders of magnitude higher than the parent’s and hence, the impact of the latter is negligible.
At the BioInternational 1994 in Munich there was a nice distinction between “Need to know” and “Nice to know”. I don’t like the idea that something which is only nice to know (i.e., not used in the assessment for BE) is mandatory in a guidance. 

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• Bioequivalence assessment: Background/justification: On total (parent + glucuronide metabolite together)
  (my emphases)
  Cave: Apples & oranges. Total should be expressed as ezetimibe after correction for the molecular masses (M_ezetimibe 409.4 g·mol^–1, M_{ezetimibe glucuronide} 585.5 g·mol^–1).