Molecule

Drug Groups

approved

Description

A direct-acting vasodilator that is used as an antihypertensive agent. [PubChem]

Indication

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.

Pharmacology

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.

Toxicity

Oral LD50 in rats: 173 and 187 mg/kg

Affected Organisms

Biotransformation

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.

Absorption

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

Protein Binding

87%

Elimination

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

References

External Links