Hydralazine is a vasodilator used by mouth for hypertension (including in pregnancy) and by injection for hypertensive emergencies and severe pre-eclampsia. It lowers blood pressure by directly relaxing artery muscles.
Also known as: Apresoline
Hydralazine causes reflex tachycardia, usually controlled by metoprolol; stopping the beta-blocker exposes the tachycardia and ischemia risk.
Direct arterial vasodilator plus beta-blocker: classic combinations (e.g., for pregnancy hypertension) but dependent on the beta-blocker.
Heart rate, angina, blood pressure.
Palpitations, angina after stopping the beta-blocker.
The combination is intentional in several protocols; never stop the beta-blocker without replacement; monitor pulse.
DailyMed — Hydralazine Hydrochloride (reflex tachycardia; use with beta-blocker) and Metoprolol labels: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=47ad263b-ad3d-4f98-b0aa-d9e82ab6cb67
Hydralazine plus propranolol is therapeutically useful (controls reflex tachycardia), but stopping propranolol exposes the tachycardia and increases cardiac workload.
Direct arterial vasodilation by hydralazine triggers reflex tachycardia blocked by propranolol.
Heart rate, angina, blood pressure.
Sudden palpitations, chest pain.
Propranolol withdrawal must be gradual; monitor pulse and ischemic symptoms.
DailyMed — Hydralazine Hydrochloride label, reflex tachycardia (co-administration with beta-blocker): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=47ad263b-ad3d-4f98-b0aa-d9e82ab6cb67
Hydralazine bioavailability doubles when taken with food — always take it the same way to avoid blood-pressure variability.
Take with meals, always in the same way (with or without food, but consistent).
DailyMed — Apresoline (hydralazine): bioavailability increased with food; Prontuário 7.3.
Hydralazine causes reflex tachycardia — caution in ischaemic heart disease and aneurysm dissection.
Always combine with a beta-blocker to blunt reflex tachycardia.
Prontuário Terapêutico INFARMED, 7.3 (hydralazine — caution in ischaemic heart disease, aneurysm dissection).
Sodium retention and tachycardia may decompensate HF — caution; combine with diuretic.
Do not use alone in HF; combine with diuretic and/or beta-blocker.
Prontuário Terapêutico INFARMED, 7.3 (hydralazine — sodium retention, reflex tachycardia).
IV hydralazine has been used for decades in severe pregnancy hypertension/pre-eclampsia with extensive clinical experience, but systematic safety data are limited: EMC-UK notes safety "not been established" and reports of fetal tachycardia and neonatal hypoglycaemia with prolonged use. Prefer methyldopa or labetalol when available; hydralazine is reserved for hypertensive crises.
IV/IM use in hospital for hypertensive crises in pregnancy and pre-eclampsia; monitor fetal heart rate and neonatal glucose if prolonged use.
Excretion into milk is not well characterised; use with caution and monitor the infant for hypotension. Prefer methyldopa when breastfeeding.
EMC-UK (MHRA) — Hydralazine SmPC (Apresoline): https://www.medicines.org.uk/emc/product/2372/smpc (section 4.6). Prontuário Terapêutico INFARMED — 4.3.1 (hydralazine as alternative in crises).
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Direct arterial vasodilator for refractory hypertension (oral, in combination) and obstetric hypertensive emergency (IV); monotherapy is limited by reflex tachycardia and fluid retention.
Opens K+ channels and activates guanylate cyclase in arteriolar (more than venular) smooth muscle, reducing afterload; the pressure drop triggers reflex tachycardia (baroreflex), sympathetic activation and renin release — hence combination with a beta-blocker and diuretic.
Good oral absorption (> 75% for hydralazine form) but substantial first-pass metabolism (systemic bioavailability 25–55% in slow acetylators); peak 45–90 min. Food increases absorption.
Hepatic acetylation (N-acetyltransferase 2 — fast/slow acetylator polymorphism) and hydroxylation; slow acetylators have higher levels and more adverse effects (including drug-induced lupus). Metabolites excreted in urine.
3–7 h (plasma); vasodilatory action longer (vascular tissue binding). In renal failure, half-life may reach 7–16 h.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
