Further evidence for an acetylator phenotype difference in the metabolism of hydralazine in man.

1 The 0-24 h urine from hypertensive patients treated with hydralazine (100 mg twice daily) has been analysed by gas chromatography and high pressure liquid chromatography. 2 4-N-Acetylhydrazinophthalazine-1-one (NAcHPZ), s-triazolo [3, 4-a] phthalazine (TP), phthalazinone (PZ) and hydralazine (free, H; acid-labile hydrazones, HH) were detected and assayed. 3 The results indicate that slow acetylators excrete less NAcHPZ and TP than rapid acetylators but more PZ and HH. 4 Free hydralazine was present in low levels and was only detected in some urine samples. 5 The ratios of the metabolites NAcHPZ/HH; TP/HH; NAcHPZ/PZ and PZ/TP are different in the two acetylator phenotypes. 6 It is possible the ratio PZ/TP may be used for determination of acetylator phenotype. 7 It is concluded that hydralazine metabolism is dependent on the acetylator phenotype.