Hydralazine

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Hydralazine

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Hydralazine is a commonly prescribed vasodilator used primarily in the management of hypertension and congestive heart failure. It is recognized for its direct arteriolar dilation effects.

Pharmacology

Mechanism of Action

Hydralazine exerts its therapeutic effects by directly relaxing the smooth muscle cells of the arterioles. This leads to an overall decrease in blood pressure. The exact molecular mechanism remains elusive, but it is believed to involve interference with calcium movement within vascular smooth muscle.

Pharmacokinetics

• Absorption: Well-absorbed orally, with an onset of action within 20-30 minutes post-administration.
• Distribution: It is widely distributed throughout the body.
• Metabolism: Primarily metabolized in the liver through acetylation.
• Excretion: Elimination is mostly through the kidneys, with a half-life ranging from 3 to 7 hours, depending on the acetylator status of the patient.

Liver safety of Hydralazine

Hydralazine has been linked to several forms of acute liver injury as well as a lupus-like syndrome.

Mechanism of action of Hydralazine

Hydralazine (hye dral' a zeen) is a phthalazine derivative and antihypertensive agent which acts by direct relaxation of arteriolar smooth muscle, probably by alteration in intracellular calcium signaling.

FDA approval information for Hydralazine

Hydralazine was one of the first oral antihypertensive medications introduced into clinical medicine and was first used in the late 1950s, but was officially approved for use in the United States in 1984. The vasodilation caused by hydralazine is followed by reflex sympathetic response that may partially reverse its antihypertensive effects. Nevertheless, when combined with other antihypertensive medications, hydralazine is effective in lowering blood pressure and it is still widely used, with more than 2 million prescriptions for hydralazine being filled yearly in the United States.

Clinical Uses

• Hypertension: Used either alone or in conjunction with other antihypertensive agents.
• Heart Failure: Employed alongside nitrates in patients with congestive heart failure to enhance cardiac output.

Side Effects

Common side effects include:

• Headaches
• Palpitations
• Tachycardia
• Nausea
• Flushing

Hydralazine may also cause a syndrome similar to lupus erythematosus, which is more frequent in patients who are slow acetylators.

Contraindications

Hydralazine should be used with caution in patients with:

• Coronary artery disease
• Mitral valvular rheumatic heart disease

Drug Interactions

Concurrent use of hydralazine with other antihypertensive agents can amplify the blood pressure-lowering effects, thereby necessitating dose adjustments. Moreover, the drug may also potentiate the actions of other vasodilators and beta-blockers.

Dosing

Dosage must be individualized depending on the clinical scenario and the patient's response. In hypertension, the initial dose may be 10 mg four times daily, gradually increasing based on patient response.

Special Considerations

Hydralazine can lead to a reflex tachycardia due to its vasodilatory effects. To counteract this, it is often co-prescribed with a beta-blocker.

References

• Pharmacotherapy: A Pathophysiologic Approach. DiPiro JT, Talbert RL, Yee GC, et al, eds.
• Handbook of Nonprescription Drugs. Krinsky D, Ferreri S, Hemstreet B, et al, eds.

Antihypertensive agents

• Dailymed label info on Hydralazine
• FDA Hydralazine

Hydralazine Resources
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