= Drug metabolism
<Drug metabolism> chemically transforms a <drug> into other molecular forms. Oxidation, hydrolysis and conjugation are common routes, frequently involving the <liver> but also other <tissues>. Transformation may inactivate a compound, generate an active product or activate a precursor; metabolism therefore does not mean detoxification in every case. <Population Pharmacokinetics Guidance for Industry by the FDA>[2022, Background and covariate analysis: pharmacokinetic variability and elimination-related factors]{ref}
The parent compound and each product have their own time courses. In a simple pathway $D\to M\to$ further products, a fall in $D$ can coexist with a rise in an active metabolite $M$. Measuring only the parent can therefore misrepresent pharmacologically relevant exposure. Chemical conversion, excretion of unchanged material and movement into a different <tissue> are distinct processes.
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