Hydralazine

Hydralazine is a vasodilator available in oral and injectable forms that is used to treat hypertension and to manage heart failure in combination with other agents. It is a direct-acting vasodilator that relaxes vascular smooth muscle, primarily in arteries, reducing systemic vascular resistance and afterload. The exact mechanism is not fully understood; it is thought to involve direct smooth muscle relaxation and, in some cases, release of nitric oxide leading to increased cGMP. Reflex sympathetic activation can occur, often resulting in tachycardia and fluid retention.

Medical uses include treatment of chronic hypertension, where hydralazine may be used alone or with other antihypertensives. In heart failure with reduced ejection fraction, it is used in combination with isosorbide dinitrate to improve symptoms and survival in select patients. It is also employed in hypertensive emergencies via intravenous administration. In pregnancy, hydralazine has been used to treat severe hypertension when indicated, such as in preeclampsia.

Pharmacokinetics and safety: Hydralazine is well absorbed orally; peak effects occur within about 30 to 60 minutes, and the duration is several hours. It is metabolized in the liver, with substantial genetic variation in acetylation that can affect response and risk of adverse effects. It is excreted in urine. Common adverse effects include tachycardia, edema, headache, dizziness, flushing, and palpitations. A drug-induced lupus-like syndrome may occur with prolonged use, particularly in slow acetylators.

Contraindications and interactions: The drug is contraindicated in individuals with hypersensitivity to hydralazine. It should be used with caution in patients with tachyarrhythmias or ischemic heart disease due to potential increases in heart rate and myocardial oxygen demand; monitor for hypotension. Hydralazine can interact with other antihypertensives to augment hypotension; NSAIDs may attenuate its antihypertensive effect. In heart failure, it is often used together with nitrates.