Dear Professor John H.T. Luong,

Thank you for your kind response.

I meant that to evaluate in vitro CYP450 isozymes inhibition activity of a drug candidate in Pharmacokinetics, the single probe substrate approach is commonly used. To be more specific, we incubate the drug candidate with the CYP450 isozyme-specific probe substrate (for example, phenacetin is specifically metabolized by CYP450 1A2 according to FDA recommendation) and metabolizing factors.

However, a drug candidate can inhibit more than one CYP450 isozyme; then, we have to conduct many separate single substrate experiments. The process is time-consuming and costly.

Hence, we would like to develop a substrate cocktail consisting of several CYP450 isozyme-specific probe substrates that we can use to assess the inhibition activity of a drug candidate on several CYP450 isozymes simultaneously.

This is our purpose, but I do not know how to design an accurate substrate cocktail and what criteria to assess it.

If convenient for you, could you please give me your valuable advice and references?

Many thanks, 

We can use the folowing drugs: Midazolam (CYP3A4 Inhibitor), Caffeine (CYP1A2 Inhibitor) , Losartan (CYP2C9 Inhibitor) , Omeprazole (CYP2C19 Inhibitor) , ansd Dextromethorphan (CYP2D6 Inhibitor) , and , separatelly : Rifampicin (CYP3A4 Induction). Concentration for each one depending of their IC50 for each cyp

 Thank you so much, Imad Hanna, Laura Garcia Capdevila.

Hi Udomsak Udomnilobol,

Thank you so much for your highly kind reply.

What you mentioned above is right. I would like to develop a new cocktail assay by which I can determine many lead candidates as inhibitors at one time.

However, the interactions among substrates have been the biggest concern in developing a reliable cocktail assay. To my knowledge, until now there have not been any papers which have been successful in designing a perfect cocktail assay in terms of the good correlation of IC50 values and enzyme activities obtained in single substrate assay and substrate cocktail assay.

I hope we could find the solutions to overcome this issue and produce a reliable cocktail assay in in vitro drug-drug interaction studies.