Determination of procainamide acetylator status

Variation in renal function can obscure the measurement of acetylator status for compounds such as procainamide in which appreciable active drug or acetyl metabolite is excreted in urine. Computer simulations and patient studies were used to compare two common metabolite/drug ratio methods and a proposed clearance technique for phenotyping acetylation rate. The calculation of apparent acetylation clearance from steady-state serum concentrations of procainamide and urinary excretion rates of N-acetyl-procainamide provides the most definitive discrimination between fast and slow acetylators.