Hydralazine
Hydralazine
Apresoline (historical); mostly generic; combination with isosorbide dinitrate marketed as BiDil for self-identified Black patients with HFrEF
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Summary
Pharmacy
Starting dose
PO 10 mg QID; IV 5-10 mg every 20-30 minutes for hypertensive emergency
Preparations
10, 25, 50, 100 mg tablets; 20 mg/mL IV
US FDA Max
300 mg/d typical practical limit (toxicity rises sharply above)
Pharmacology
Routes
Oral, IV, IM
Onset
IV: 5-20 minutes; PO: 30-60 minutes
Duration
IV: 1-4 hours; PO: 3-8 hours
Half-life
3-7 hours (slow acetylators) vs 1-3 hours (rapid acetylators) via NAT2 polymorphism[1]
Bioavailability
~25-50% (oral; substantial first-pass via NAT2 acetylation, phenotype-dependent)[1]
Pregnancy
One of the historically preferred IV agents for severe hypertension in pregnancy alongside labetalol and nifedipine.[citation needed]
Legal status
Rx-only in US
Purported mechanism
Hydralazine relaxes arteriolar smooth muscle predominantly (with little venous effect), reducing systemic vascular resistance; the mechanism is incompletely understood but involves interference with IP3-induced calcium release from sarcoplasmic reticulum and possibly cGMP elevation.0 Reflex sympathetic activation (tachycardia, sodium retention) is the dose-limiting effect; pairing with a β-blocker and a diuretic blunts both. Drug-induced lupus is the recognized chronic-use toxicity, with risk concentrated in slow acetylators (NAT2 phenotype) and disproportionate in women; antinuclear antibody positivity is common at higher chronic doses[1].
References
- ↑ 1.0 1.1 1.2 FDA Prescribing Information, hydralazine HCl, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/008303s069lbl.pdf