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Direct-Acting Vasodilator — Hypertensive Emergency / Chronic Hypertension Pregnancy: Used in pregnancy (pre-eclampsia) — relatively well-established safety; neonatal thrombocytopaenia reported with prolonged use

Hydralazine

Brand names: Apresoline

Adult dose

Dose: Hypertensive emergency: 5–10 mg IV slowly over 20 minutes; repeat after 20–30 min if needed; Chronic: 25 mg 2–3 times daily orally
Route: Intravenous (emergency) or oral (chronic)
Frequency: IV: repeat as needed (max 3–4 doses); Oral: 2–3 times daily
Max: IV: 20 mg per dose; Oral: 200 mg/day
IV hydralazine primarily used in hypertensive emergencies in pregnancy (eclampsia/pre-eclampsia) — labetalol or nifedipine now preferred in most UK guidelines. Oral: rarely used for chronic hypertension in UK (superseded by modern agents). Give with food (oral). Fast acetylators require higher doses.

Paediatric dose

Dose: 0.1–0.5 mg/kg IV mg/kg
Route: IV or oral
Frequency: Every 4–6 hours as needed
Max: 20 mg IV per dose
BNFc: used in hypertensive emergencies in children under specialist guidance

Dose adjustments

Renal

CrCl <30 mL/min: extend dosing interval (every 8–16 hours); slow acetylators accumulate more

Hepatic

Use with caution — hepatically metabolised by N-acetyltransferase

Paediatric weight-based calculator

BNFc: used in hypertensive emergencies in children under specialist guidance

Clinical pearls

  • Drug-induced lupus is the major long-term risk — typically at doses >200 mg/day and in slow acetylators (NAT2 polymorphism); monitor ANA; usually reversible on stopping
  • In pre-eclampsia: hydralazine IV was historical standard; NICE now recommends labetalol IV (first-line), nifedipine oral, or hydralazine IV — all equivalent; labetalol most predictable response
  • Reflex tachycardia is significant — always co-prescribe beta-blocker in chronic use
  • Dissecting aortic aneurysm: contraindicated — increased cardiac output worsens aortic wall stress; use beta-blocker + sodium nitroprusside instead
  • Peripheral neuropathy with chronic use — supplement with pyridoxine (vitamin B6) 25 mg/day

Contraindications

  • Idiopathic systemic lupus erythematosus (SLE) or drug-induced lupus
  • Cor pulmonale
  • Myocardial insufficiency due to mechanical obstruction
  • Dissecting aortic aneurysm (increases cardiac output — dangerous)

Side effects

  • Reflex tachycardia
  • Headache
  • Flushing
  • Nausea
  • Fluid retention
  • Drug-induced lupus syndrome (>200 mg/day, slow acetylators — ANA positive)
  • Peripheral neuropathy (pyridoxine deficiency)
  • Hypotension

Interactions

  • Beta-blockers — reduce reflex tachycardia (often co-prescribed)
  • Other antihypertensives — additive hypotension
  • MAOIs — enhanced hypotensive effect

Monitoring

  • Blood pressure (continuous IV monitoring)
  • Heart rate (reflex tachycardia)
  • ANA and anti-dsDNA (long-term oral use)
  • FBC (lupus-like blood dyscrasias)

Reference: BNFc; BNF 90; NICE NG133 (Hypertension in Pregnancy); Magee et al. NEJM 2015; NICE NG136. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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