Bioequivalence and Bioavailability Forum

Hi Mutasim,

reading the guidance again I understand your confusion.

On top of page 3 we have

Analyte: ☐ parent ☐ metabolite ☒ both
Background: Ezetimibe undergoes extensive pre-systemic metabolism; ezetimibe-glucuronide is the major active metabolite. Because of extensive hepatic recirculation, the exposure to ezetimibe is less representative to evaluate absorption.

And then

Bioequivalence assessment: Background/justification: On total (parent + glucuronide metabolite together)

(my emphases)

Analyte: ☒ both seemingly tells us to measure them separately but the remainder tells us that only the total should be assessed for BE. So why all that fuzz?

I still think that cleaving by glucuronidase and analyzing ezetimibe is the way to go. What I wrote above was based on extraction techniques (SPE, LLE). If you opt for protein precipation it could work but as a hydrophilic compound it might well be that some part of the glucuronide gets trapped in the precipitate. I also believe that you need two chromatographic conditions. Furthermore, glucuronides are known for back-conversion in the ion-source. Hence, what you might get are wrong values for both the parent and the metabolite but the sum will be correct (assuming that nothing of the glucuronide gets trapped – what I doubt). Hence, I would keep it simple and go for cleavage and have just one run.
If the EMA really want both separatelly IMHO, it would have been better to state in the GL:

Analyte: ☒ parent ☒ metabolite ☐ both

Out of curiosity: Since dealing with glucuronides was the topic of my first paper* – which stationary & mobile phase are you using?

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• Mascher H, Nitsche V, Schütz H. Separation, isolation and identification of optical isomers of 1,4-benzodiazepine glucuronides from biological fluids by reversed-phase high-performance liquid chromatography. J Chr B. 1984; 231–9. doi:10.1016/S0378-4347(00)80885-3.