Difference between revisions of "Hydralazine"

Revision as of 14:08, 6 July 2010

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 and decreasing afterload.^[1]

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:

• Diarrhea
• Compensatory tachycardia due to baroreceptor reflex
• Headache
• Loss of appetite
• Nausea or vomiting
• Depression
• Pounding heartbeat
• Drug-Induced Lupus Erythematosus^[6]

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.^{[citation needed]}

See also

• Cadralazine
• Dihydralazine
• Endralazine

References

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1. ↑ ^{1.0 1.1 1.2 1.3} Harvey, Richard A., Pamela A. Harvey, and Mark J. Mycek. Lippincott's Illustrated Reviews: Pharmacology. 2nd ed. Philadelphia: Lipincott, Williams & Wilkins, 2000. 190.
2. ↑ Rang, Dale, Ritter and Flower. Pharmacology. 6th Ed, 2007.
3. ↑ "antihtn". Retrieved 2008-10-05. 
4. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
5. ↑ Bhushan, Vikas, Tao T. Lee, and Ali Ozturk. First Aid for the USMLE Step 1. New York: McGraw-Hill Medical, 2007. 251.
6. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.