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Systematic (IUPAC) name
phthalazin-1-yl hydrazine
CAS number 86-54-4
ATC code C02DB02
PubChem 3637
Chemical data
Formula C8H8N4 
Mol. mass 160.176 g/mol
Pharmacokinetic data
Bioavailability  ?
Metabolism  ?
Half life  ?
Excretion  ?
Therapeutic considerations
Pregnancy cat.


Legal status
Routes Oral, intravenous

Hydralazine hydrochloride (1-hydrazinophthalazine monohydrochloride; Apresoline) is a direct-acting smooth muscle relaxant used to treat hypertension by acting as a vasodilator primarily in arteries and arterioles. By relaxing vascular smooth muscle, vasodilators act to decrease peripheral resistance, thereby lowering blood pressure.[1]



Hydralazine works through a cGMP-mediated mechanism, resulting in smooth muscle relaxation.[2]

Clinical Use

Hydralazine is not used as a primary drug for treating hypertension because it elicits a reflex sympathetic stimulation of the heart (the baroreceptor reflex). The sympathetic stimulation may increase heart rate and cardiac output, and may cause angina pectoris or myocardial infarction.[1] Hydralazine may also increase plasma renin concentration, resulting in fluid retention. In order to prevent these undesirable side effects, hydralazine is generally prescribed in combination with a beta-blocker (e.g., propranolol) and a diuretic.[1]

Hydralazine is used to treat severe hypertension, but again, it is not a first line therapy for essential hypertension. However, hydralazine is the first line therapy for hypertension in pregnancy, with methyldopa.[2]

Side effects

Common side effects include:

Patients given hydralazine over a peroid of six months may develop a lupus-like syndrome or other immune related diseases that generally are reversible with withdrawal.[1] Hydralazine is differentially acetylated by fast and slow acetylator phenotypes thus incidence of lupus-like disease in slow acetylators.


  1. ^ a b c d Harvey, Richard A., Pamela A. Harvey, and Mark J. Mycek. Lippincott's Illustrated Reviews: Pharmacology. 2nd ed. Philadelphia: Lipincott, Williams & Wilkins, 2000. 190.
  2. ^ a b Bhushan, Vikas, Tao T. Lee, and Ali Ozturk. First Aid for the USMLE Step 1. New York: McGraw-Hill Medical, 2007. 251.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hydralazine". A list of authors is available in Wikipedia.
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