BIOTRANSFORMATION (Metabolism) Biotransformation reactions can be classified into: (a)Nonsynthetic/PhaseI/Functionalization reactions: a functional group is generated or exposed-- metabolite may be active or inactive. (b) Synthetic/Conjugation/ Phase II reactions: an endogenous radical is conjugated to the drug-- metabolite is mostly inactive; except few drugs, e.g. glucuronide conjugate of morphine and sulfate conjugate of minoxidil are active. Acetylation:- Compounds having amino or hydrazine residues are conjugated with the help of acetyl coenzyme-A, e.g. sulfonamides, isoniazid, PAS, dapsone, hydralazine, clonazepam, procainamide. Multiple genes control the N-acetyl transferases (NATs), and rate of acetylation shows genetic polymorphism (slow and fast acetylators). Ref:- kd tripathi; pg num:-22,24