Skeletal formula of hydralazine
Ball-and-stick model of the hydralazine molecule
Clinical data
Trade names Apresoline
AHFS/Drugs.com Monograph
MedlinePlus a682246
License data
  • AU: C
  • US: C (Risk not ruled out)
Routes of
By mouth, intravenous
ATC code C02DB02 (WHO)
Legal status
Legal status
Pharmacokinetic data
Bioavailability 26–50%
Protein binding 85–90%
Metabolism Liver
Biological half-life 2–8 hours, 7–16 hours (renal impairment)
Excretion Urine
CAS Number 86-54-4 YesY
PubChem (CID) 3637
DrugBank DB01275 YesY
ChemSpider 3511 YesY
KEGG D08044 YesY
ECHA InfoCard 100.001.528
Chemical and physical data
Formula C8H8N4
Molar mass 160.176 g/mol
3D model (Jmol) Interactive image

Hydralazine (trade name Apresoline) is a direct-acting smooth muscle relaxant used to treat hypertension by acting as a vasodilator primarily in arteries and arterioles. By relaxing vascular smooth muscle, vasodilators act to decrease peripheral resistance, thereby lowering blood pressure and decreasing afterload.[1]

However, this only has a short term effect on blood pressure, as the system will reset to the previous, high blood pressure needed to maintain pressure in the kidney necessary for natriuresis. The long-term effect of antihypertensive drugs comes from their effects on the pressure natriuresis curve. It belongs to the hydrazinophthalazine class of drugs.[2]

It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.[3]

Medical use

Hydralazine is not used as a primary drug for treating hypertension because it elicits a reflex sympathetic stimulation of the heart (the baroreceptor reflex).[4] The sympathetic stimulation may increase heart rate and cardiac output, and in patients with coronary artery disease may cause angina pectoris or myocardial infarction.[1] Hydralazine may also increase plasma renin concentration, resulting in fluid retention. To prevent these undesirable side effects, hydralazine is usually prescribed in combination with a β-blocker (e.g., propranolol) and a diuretic.[1] In the UK, labetalol tends to be the first-line β-blocker.

Hydralazine is used to treat severe hypertension, but again, it is not a first-line therapy for essential hypertension. However, hydralazine is the first-line therapy for hypertension in pregnancy, with methyldopa.[5] It has also been used successfully as a treatment for myelodysplastic syndrome in its capacity as a DNA methyltransferase inhibitor.[6]

Hydralazine is commonly used in combination with isosorbide dinitrate for the treatment of congestive heart failure in self-identified African American populations. This preparation, BiDil, was the first race-based prescription drug.

Side effects

Very common (>10% frequency) side effects include:[7]

Common (1–10% frequency) side effects include:[7][8]

Uncommon (0.1–1% frequency) side effects include:[7][8]

Rare (<0.1% frequency) side effects include:[7][8]


Contraindications include:[7]


It may potentiate the antihypertensive effects of:[7]

Drugs subject to a strong first-pass effect such as β-blockers may increase the bioavailability of hydralazine.[7] Epinephrine (adrenaline)'s heart rate-accelerating effects are increased by hydralazine, hence may lead to toxicity.[7]

Mechanism of action

Hydralazine causes arterial vasodilation by an, as of yet, unclarified mechanism. Hydralazine requires the endothelium to provide nitric oxide,[9] thus only causes vasodilation in vivo with functional endothelium. Hydralazine will not cause vasodilation in vitro in an isolated blood vessel.

Activation of hypoxia-inducible factors has been suggested as a mechanism.[10]

See also


  1. 1 2 3 Harvey, Richard A., Pamela A. Harvey, and Mark J. Mycek. Lippincott's Illustrated Reviews: Pharmacology. 2nd ed. Philadelphia: Lipincott, Williams & Wilkins, 2000. 190.
  2. Bourreli, B.; Pinaud, M.; Passuti, N.; Gunst, J. P.; Drouet, J. C.; Remi, J. P. (1988). "Additive effects of dihydralazine during enflurane or isoflurane hypotensive anaesthesia for spinal fusion". Canadian Journal of Anesthesia. 35 (3): 242–8. doi:10.1007/BF03010617. PMID 3383316.
  3. "WHO Model List of EssentialMedicines" (PDF). World Health Organization. October 2013. Retrieved 22 April 2014.
  4. Kandler MR, Mah GT, Tejani AM, Stabler SN, Salzwedel DM. Hydralazine for essential hypertension. Cochrane Database of Systematic Reviews 2011, Issue 11. Art. No.: CD004934. DOI: 10.1002/14651858.CD004934.pub4.
  5. Bhushan, Vikas, Tao T. Lee, and Ali Ozturk. First Aid for the USMLE Step 1. New York: McGraw-Hill Medical, 2007. 251.
  6. Candelaria, M; Herrera, A; Labardini, J; González-Fierro, A; Trejo-Becerril, C; Taja-Chayeb, L; Pérez-Cárdenas, E; Cruz-Hernández, E; Arias-Bofill, D; Vidal, S; Cervera, E; Dueñas-Gonzalez, A (5 October 2010). "Hydralazine and magnesium valproate as epigenetic treatment for myelodysplastic syndrome. Preliminary results of a phase-II trial". Annals of Hematology. 90 (4): 379–387. doi:10.1007/s00277-010-1090-2. PMID 20922525.
  7. 1 2 3 4 5 6 7 8 "PRODUCT INFORMATION APRESOLINE® (hydralazine hydrochloride 20 mg powder for injection ampoule)" (PDF). TGA eBusiness Services. Link Medical Products Pty Ltd. 27 March 2005. Retrieved 13 February 2014.
  8. 1 2 3 Rossi, S, ed. (2013). Australian Medicines Handbook (2013 ed.). Adelaide: The Australian Medicines Handbook Unit Trust. ISBN 978-0-9805790-9-3.
  9. "antihtn". Retrieved 2008-10-05.
  10. Knowles HJ, Tian YM, Mole DR, Harris AL (July 2004). "Novel mechanism of action for hydralazine: induction of hypoxia-inducible factor-1alpha, vascular endothelial growth factor, and angiogenesis by inhibition of prolyl hydroxylases". Circ. Res. 95 (2): 162–9. doi:10.1161/01.RES.0000134924.89412.70. PMID 15192023.
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