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Home / Drugs / Starting with H / Hydralazine

A direct-acting vasodilator that is used as an antihypertensive agent. [PubChem]
CategoriesAntihypertensive Agents
Vasodilator Agents
ManufacturersNovartis pharmaceuticals corp
Abraxis pharmaceutical products
Akorn inc
App pharmaceuticals llc
Luitpold pharmaceuticals inc
Smith and nephew solopak div smith and nephew
Solopak laboratories inc
Teva parenteral medicines inc
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Superpharm corp
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Usl pharma inc
Vangard laboratories inc div midway medical co
Vitarine pharmaceuticals inc
Watson laboratories inc
West ward pharmaceutical corp
Zydus pharmaceuticals usa inc
PackagersAdvanced Pharmaceutical Services Inc.
American Regent
Amerisource Health Services Corp.
APP Pharmaceuticals
A-S Medication Solutions LLC
Camber Pharmaceuticals Inc.
Cardinal Health
Caremark LLC
Direct Dispensing Inc.
DispenseXpress Inc.
Dispensing Solutions
Diversified Healthcare Services Inc.
General Injectables and Vaccines Inc.
Glenmark Generics Ltd.
Goldline Laboratories Inc.
Heartland Repack Services LLC
Heritage Pharmaceuticals
Hetero Drugs Ltd.
Ivax Pharmaceuticals
Kaiser Foundation Hospital
Lake Erie Medical and Surgical Supply
Luitpold Pharmaceuticals Inc.
Major Pharmaceuticals
Mckesson Corp.
Murfreesboro Pharmaceutical Nursing Supply
Mutual Pharmaceutical Co.
Nucare Pharmaceuticals Inc.
Palmetto Pharmaceuticals Inc.
Par Pharmaceuticals
PD-Rx Pharmaceuticals Inc.
Physicians Total Care Inc.
Pliva Inc.
Prepackage Specialists
Prepak Systems Inc.
Remedy Repack
Sandhills Packaging Inc.
Southwood Pharmaceuticals
Teva Pharmaceutical Industries Ltd.
UDL Laboratories
United Research Laboratories Inc.
Vangard Labs Inc.
SynonymsHydralazine hydrochloride


For the treatment of essential hypertension, alone or as an adjunct. Also for the management of severe hypertension when the drug cannot be given orally or when blood pressure must be lowered immediately, congestive heart failure (in combination with cardiac glycosides and diuretics and/or with isosorbide dinitrate), and hypertension secondary to pre-eclampsia/eclampsia.


A vasodilator, hydralazine works by relaxing blood vessels (arterioles more than venules) and increasing the supply of blood and oxygen to the heart while reducing its workload. It also functions as an antioxidant. It inhibits membrane-bound enzymes that form reactive oxygen species, such as superoxides. Excessive superoxide counteracts NO-induced vasodilation. It is commonly used in the condition of pregnancy called preeclampsia.

mechanism of action

Although the precise mechanism of action of hydralazine is not fully understood, the major effects are on the cardiovascular system. Hydralazine apparently lowers blood pressure by exerting a peripheral vasodilating effect through a direct relaxation of vascular smooth muscle. It has also been suggested that cyclic 3',5'-adenosine monophosphate (cyclic AMP) mediates, at least partly, the relaxation of arterial smooth muscle by altering cellular calcium metabolism, which interferes with the calcium movements within the vascular smooth muscle that are responsible for initiating or maintaining the contractile state. In hypertensive patients, the hydralazine-induced decrease in blood pressure is accompanied by increased heart rate, cardiac output, and stroke volume, probably because of a reflex response to decreased peripheral resistance. The drug has no direct effect on the heart. Hydralazine may increase pulmonary arterial pressure, as well as coronary, splanchnic, cerebral, and renal blood flow. The preferential dilatation of arterioles, as compared to veins, minimizes postural hypotension and promotes the increase in cardiac output. Hydralazine usually increases renin activity in plasma, presumably as a result of increased secretion of renin by the renal juxtaglomerular cells in response to reflex sympathetic discharge. This increase in renin activity leads to the production of angiotensin II, which then causes stimulation of aldosterone and consequent sodium reabsorption. Tolerance to the antihypertensive effect of the drug develops during prolonged therapy, especially if a diuretic is not administered concurrently. In patients with CHF, hydralazine decreases systemic vascular resistance and increases cardiac output.


Oral LD50 in rats: 173 and 187 mg/kg


Hydralazine, when administered orally, undergoes extensive first-pass metabolism by genetic polymorphic acetylation, which is responsible for a threefold range of oral bioavailability. Intravenously administered hydralazine does not undergo first-pass metabolism and, therefore, is not affected by acetylator phenotype. After the drug reaches the systemic circulation, it is combined with endogenous aldehydes and ketones, including pyruvic acid, to form hydrazone metabolites. The active metabolites, hydralazine acetonide hydrazone and hydralazine pyruvate hydrazone, are equipotent with the parent, hydralazine.


Hydralazine is rapidly and extensively absorbed (up to 90%) from the gastrointestinal tract and undergoes extensive first-pass metabolism by genetic polymorphic acetylation. Oral bioavailability of hydralazine is dependent upon acetylator phenotype. Bioavailability is approximately 31% in slow acetylators and 10% in fast acetylators.

half life

3 to 7 hours

route of elimination

Hydralazine undergoes extensive hepatic metabolism; it is excreted mainly in the form of metabolites in the urine.

drug interactions

Metoprolol: Increased effect of both drugs

Propranolol: Increased effect of both drugs

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.