Should the Acetylator Phenotype Be Determined when Prescribing Hydralazine for Hypertension?

The role of acetylator phenotype in determining the response to hydralazine when it was added to diuretic and beta-blocker at doses not exceeding 200 mg daily was examined in 57 hypertensive patients. 81% of rapid acetylators needed 200 mg hydralazine daily compared to 38% of slow acetylators (p less than 0.01). Despite higher doses of hydralazine the blood pressure was controlled in only 27% of rapid acetylators compared to 65% of slow acetylators (p less than 0.02). The relation of acetylator phenotype to blood pressure response was statistically independent of initial blood pressure, age, sex, body weight and serum creatinine (p less than 0.005). Current recommendations on hydralazine dosage are unsatisfactory for the 40% of hypertensive patients who are rapid acetylators. We suggest measurement of the acetylator phenotype in patients who respond incompletely to 200 mg hydralazine daily. About 70% of these patients will be rapid acetylators in whom the dose of hydralazine can be increased safely.