I'm working with PK data of drug X that is majorly excreted unchanged into the urine (60-70%), but also has one metabolite excreted into the urine (30-40%). AUC and Ae of drug X and Ae(m) were measured. Metabolite concentrations in plasma were very low and undetectable. Thus, I was using the following equation to estimate formation clearance of the metabolite:
Cf = Ae(m) / AUC (of drug X).
However, this equation assume that all drug X is metabolized F(m) = 1. That's not the case. Thus, how to estimate formation clearance when F(m) is not unity?
Additionally, metabolism seems to be occurring in a higher extend in the kidneys, not the liver.
Thank you!
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