Hydralazine |
Hydralazine hydrochloride (1-hydrazinophthalazine monohydrochloride; 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. Mechanism Hydralazine works through a cGMP-mediated mechanism, resulting in smooth muscle relaxation. 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. Hydralazine may also increase plasma renin concentration, resulting in fluid retention. In order to prevent these undesirable side effects, hydralazine is generally prescribed in combination with a beta-blocker (e.g., propranolol) and a diuretic. 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. Side effects Common side effects include: Diarrhea Compensatory tachycardia due to baroreceptor reflex Headache Loss of appetite Nausea or vomiting Pounding heartbeat Drug-Induced Lupus Erythematosus Patients given hydralazine over a peroid of six months may develop a lupus-like syndrome or other immune related diseases that generally are reversible with withdrawal. Hydralazine is differentially acetylated by fast and slow acetylator phenotypes thus incidence of lupus-like disease in slow acetylators. |