Determinants of response to intravenous hydralazine in hypertension

There is marked interindividual variation in hypotensive response to intravenous hydralazine (H). We examined the determinants of response in patients with hypertension. After a single intravenous dose of 0.3 mglkg H, response was correlated independently (r = 0.8364) with both predrug blood pressure and acetylator index (AI). Intravenous dose ranging studies showed that response also depended on the amount of H in the systemic circulation. Although plasma H levels depend on AI after oral doses, this is not so after intravenous administration. AI must therefore affect response to H by an alternative, presumably nonmetabolic mechanism which, after oral dosing, would add to its effect on H levels. Response to intravenous nitroprusside was not related to AI, perhaps indicating specificity of this effect for H. These data reinforce the potential usefulness of determining Al before giving H to a patient. Clinical Pharmacology and Therapeutics (1981) 30 , 773–781; doi: 10.1038/clpt.1981.237