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Hydralazine
Systematic (IUPAC) name
1-hydrazinylphthalazine
Identifiers
CAS number 86-54-4
ATC code C02DB02
PubChem 3637
ChemSpider 3511
Chemical data
Formula C 8H8N4  
Mol. mass 160.176 g/mol
Pharmacokinetic data
Bioavailability 26-55%
Metabolism Hepatic
Half life 2-4 hours
Excretion Renal
Therapeutic considerations
Pregnancy cat. C
Commonly used to treat severe PIH
Legal status
Routes Oral, intravenous
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Hydralazine (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.[1]

Contents

Mechanism of Action

The mechanism of action of hydralazine is not well known. It interferes with the action of the second messenger IP3, limiting calcium release from the sarcoplasmic reticulum of smooth muscle. This results in an arterial and arteriolar relaxation.[2]

It recently has been identified as a nitric oxide donor.[3]

Activation of hypoxia-inducible factors has been suggested as a mechanism.[4]

Clinical 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). The sympathetic stimulation may increase heart rate and cardiac output, and may cause angina pectoris or myocardial infarction.[1] Hydralazine may also increase plasma renin concentration, resulting in fluid retention. In order to prevent these undesirable side-effects, hydralazine is usually prescribed in combination with a beta-blocker (e.g., propranolol) and a diuretic.[1]

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]

Side effects

Common side-effects include:

Patients given hydralazine over a period of six months may develop a lupus-like syndrome or other immune-related diseases that, in general, are reversible with withdrawal.[1] Hydralazine is differentially acetylated by fast and slow acetylator phenotypes, hence incidence of lupus-like disease in slow acetylators.

See also

References

  1. ^ a b c d Harvey, Richard A., Pamela A. Harvey, and Mark J. Mycek. Lippincott's Illustrated Reviews: Pharmacology. 2nd ed. Philadelphia: Lipincott, Williams & Wilkins, 2000. 190.
  2. ^ Rang, Dale, Ritter and Flower. Pharmacology. 6th Ed, 2007.
  3. ^ "antihtn". http://faculty.swosu.edu/scott.long/phcl/antihtn.htm. Retrieved 2008-10-05.  
  4. ^ 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. http://circres.ahajournals.org/cgi/pmidlookup?view=long&pmid=15192023.  
  5. ^ Bhushan, Vikas, Tao T. Lee, and Ali Ozturk. First Aid for the USMLE Step 1. New York: McGraw-Hill Medical, 2007. 251.
  6. ^ Mazari L, Ouarzane M, Zouali M (April 2007). "Subversion of B lymphocyte tolerance by hydralazine, a potential mechanism for drug-induced lupus". Proc. Natl. Acad. Sci. U.S.A. 104 (15): 6317–22. doi:10.1073/pnas.0610434104. PMID 17404230. PMC 1851062. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=17404230.  







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