Oskela
Get started

Drug Reference

hydralazine

vasodilator· Brands: Apresoline, ApressolineIVPO

Mechanism of action
Hydralazine causes direct relaxation of arteriolar smooth muscle, leading to vasodilation and a reduction in peripheral vascular resistance. The exact mechanism is not fully understood, but it appears to involve interference with intracellular calcium availability and possibly the release of nitric oxide. This action is relatively selective for arterioles, with minimal effect on veins, and results in reflex sympathetic activation, which increases heart rate and contractility.
Pharmacokinetics
Hydralazine is well absorbed after oral administration but undergoes extensive first-pass metabolism in the liver, resulting in a variable bioavailability that depends on acetylator phenotype. It is metabolised by acetylation, with fast acetylators having lower systemic exposure. The plasma half-life is short (approximately 1 hour), but the pharmacodynamic effect persists longer due to tissue binding. Excretion is predominantly renal, as inactive metabolites.
Indications & dosing

Essential hypertension

Initial dose, titrate to response. Reflex tachycardia may occur, monitor heart rate.

  • adult · PO: 25–50 mg twice daily · Initial dose, titrate to response. Reflex tachycardia may occur, monitor heart rate.

Hypertensive emergency

Slow IV injection over 1-2 minutes. Repeat as needed. Monitor blood pressure continuously.

  • adult · IV: 5–10 mg every 20-30 min · Slow IV injection over 1-2 minutes. Repeat as needed. Monitor blood pressure continuously.

Pregnancy-induced hypertension

Used for severe hypertension in pregnancy. May cause hypotension, monitor fetal status.

  • adult · PO: 25–50 mg twice daily · Used for severe hypertension in pregnancy. May cause hypotension, monitor fetal status.

Heart failure (with isosorbide dinitrate)off-label

Off-label use in combination with isosorbide dinitrate for HFrEF. Titrate as tolerated.

  • adult · PO: 25–75 mg three times daily · Off-label use in combination with isosorbide dinitrate for HFrEF. Titrate as tolerated.

Hypertension (pediatric)

Dose based on weight. Monitor for hypotension and reflex tachycardia.

  • pediatric · PO: 0.5–1 mg/kg every 6-8 hours · Dose based on weight. Monitor for hypotension and reflex tachycardia.
Contraindications & precautions
  • Hypersensitivity to hydralazine
  • Coronary artery disease · Reflex tachycardia may precipitate angina or myocardial infarction
  • Rheumatic heart disease, especially mitral stenosis · Vasodilation may increase pulmonary arterial pressure
  • Systemic lupus erythematosus or history of drug-induced lupus · May exacerbate or induce lupus-like syndrome
  • Severe renal impairment · Metabolites accumulate; use with caution or adjust dose
  • Use with caution in patients with ischaemic heart disease as reflex tachycardia may worsen angina; consider co-administration of a beta-blocker if appropriate.
  • Monitor for symptoms of drug-induced lupus (e.g., arthralgia, fever, rash, positive antinuclear antibodies); discontinue if suspected.
  • Monitor blood pressure and heart rate regularly, especially after starting or increasing the dose.
  • Reduce dose in patients with renal impairment to avoid accumulation of metabolites.
  • Avoid rapid administration by intravenous route as it may cause severe hypotension.
Adverse effects
  • Headache
  • Palpitations/tachycardia
  • Flushing
  • Nausea/vomiting
  • Hypotension
  • Drug-induced lupus erythematosusserious
  • Angina pectoris or myocardial infarctionserious
  • Peripheral neuropathyserious
Renal & hepatic adjustment
  • eGFR 30–59: Reduce initial dose; start with 25 mg twice daily and titrate cautiously.
  • eGFR 0–29: Use with caution; consider reducing the dose and increasing the dosing interval.
  • Hepatic impairment (mild): No dose adjustment required.
  • Hepatic impairment (moderate): Use with caution; consider dose reduction.
  • Hepatic impairment (severe): Avoid. (avoid)
Monitoring, pregnancy & toxicity
  • Blood pressure · Regularly during dose titration and throughout treatment
  • Heart rate · Regularly; watch for reflex tachycardia
  • Signs of lupus-like syndrome (e.g., rash, arthralgia, fever) · Monitor periodically; consider ANA if symptoms develop
  • ANA titre · Baseline and periodically in long-term therapy
  • Renal function · Periodically in patients with renal impairment
  • Pregnancy: Hydralazine is suitable for use in pregnancy; it is commonly used to treat severe hypertension and pre-eclampsia in pregnancy.
  • Toxicity: Hypotension with reflex tachycardia · Place patient supine, give IV fluids; if severe, use vasopressors (e.g., dopamine) and continuous monitoring.
  • Toxicity: Tachycardia and arrhythmias · Monitor ECG; treat tachyarrhythmias with beta-blockers if necessary.
  • Toxicity: Headache and flushing · Supportive care; ensure adequate hydration; monitor blood pressure.
  • Toxicity: Myocardial ischaemia · Treat as per ischaemia protocols; seek specialist advice.
Clinical notes
Hydralazine is used in the treatment of hypertension, particularly in pregnancy, and in heart failure when combined with nitrates, especially in patients of African descent. A major adverse effect is drug-induced lupus erythematosus, more common in slow acetylators, so it is important to monitor for rash, arthralgia, and antinuclear antibodies. It can also cause reflex tachycardia, so may be combined with a beta-blocker. When used intravenously, it is effective for hypertensive emergencies. Doses should be titrated gradually.

Log in to read the full hydralazine monograph

A free account unlocks the complete drug reference, the interaction checker, prescription practice and every other learning tool.

Log inCreate a free account

BNF; local formulary