Direct-Acting Vasodilator — Hypertensive Emergency / Chronic Hypertension

Hydralazine

Brand names: Apresoline

Hydralazine is a direct-acting arterial vasodilator antihypertensive, used in resistant or severe hypertension, hypertension in pregnancy, and in heart failure combined with a nitrate.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Start 10 mg four times daily for the first 2 to 4 days; increase to 25 mg four times daily for the balance of the first week; then 50 mg four times daily for the second and subsequent weeks

Route: Oral

Frequency: Four times daily

Max: In a few resistant patients, up to 300 mg daily may be required; large doses carry a high incidence of toxic reactions, particularly the L.E. cell syndrome

US labelling (Hydralazine Hydrochloride tablets). Initiate in gradually increasing dosages and adjust to individual response: 10 mg four times daily for the first 2–4 days, 25 mg four times daily for the balance of the first week, then 50 mg four times daily for the second and subsequent weeks. For maintenance, adjust to the lowest effective level. In resistant patients up to 300 mg daily may be required; consider a lower hydralazine dose combined with a thiazide and/or reserpine or a beta blocker, with individual titration to the lowest therapeutic dose of each drug. UK dosing (Apresoline SPC) differs (initially 25 mg twice daily, max 200 mg daily, with acetylator-status/female-dose caveats) — verify against UK SPC.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to hydralazine
Coronary artery disease
Mitral valvular rheumatic heart disease

Side effects

Headache, anorexia, nausea, vomiting, diarrhea (common)
Palpitations, tachycardia, angina pectoris (common)
Hypotension, paradoxical pressor response, edema
Peripheral neuritis (paresthesia, numbness, tingling), dizziness, tremors
Blood dyscrasias (leukopenia, agranulocytosis, purpura); rash, urticaria, fever; rarely hepatitis

Clinical monograph

How it works

It relaxes arteriolar smooth muscle directly, reducing systemic vascular resistance and arterial blood pressure.

Prescribing in practice

Long-term or higher-dose use can cause a drug-induced lupus-like syndrome, which should prompt review and discontinuation.
Reflex tachycardia and fluid retention often require co-administration of a beta-blocker and a diuretic.
In heart failure it is combined with a nitrate, particularly where renin-angiotensin system inhibitors are unsuitable.

Monitoring

Monitor blood pressure and heart rate, and remain alert for features of a lupus-like syndrome such as arthralgia and rash.

Counselling the patient

This medicine lowers blood pressure by relaxing the blood vessels.
Report persistent joint pains, fever, rash or unusual tiredness.
Do not stop the medicine suddenly without advice.

Evidence & guidelines

The combination of hydralazine with isosorbide dinitrate improved outcomes in heart failure trials, including benefit demonstrated in self-identified Black patients in the A-HeFT trial.

Reference: NICE NG133 (Hypertension in Pregnancy); Magee et al. NEJM 2015; NICE NG136; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways