Effect of dose on acetylator phenotype distribution of hydralazine.

The effect of dose on acetylator phenotype distribution of hydralazine has been determined, The acetylated metabolites methyltriazolophthalazine (MTP) and 3-hydroxymethyltriazolophthalazine (3-OHMTP) and acid-labile hydralazine (HP) were determined in the 0- to 24-hr urine of patients receiving various doses. The difference between the mean value for the ration 3-OHMTP:HP in the rapid and slow acetylators varied with dose, the greatest difference being after a 200 mg (100 mg twice daily) dose. The distribution of the ratio became less clearly bimodal at lower doses, with overlap between phenotypes occurring at doses of 100 mg (50 mg twice daily) or less. The most effective dose for discriminating between acetylator phenotypes was found to be 200 mg (100 mg twice daily).