|Systematic (IUPAC) name|
Commonly used to treat severe PIH
|Mol. mass||160.176 g/mol|
| (what is this?)
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.
However, this only has a short term effect on blood pressure, as the system will reset to the previous, high blood pressure necessary 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.
Mechanism of action
Hydralazine binds to and activates gated potassium channels on vascular smooth muscle. The result is an efflux of potassium and a subsequent hyperpolarization of the cell. This prevents calcium-mediated activation and constriction of the smooth muscle, resulting in vasodilation. However, this induced vasodilation triggers the baroreflex resulting in tachycardia and vasoconstriction. Hydralazine is therefore not a great candidate for control of hypertension alone. It is often co-administered with a beta blocker to mitigate the effects of the baroreflex.
Hydralazine requires the endothelium to provide NO (nitric oxide. ) thus only provides the effects of NO in vivo with functional endothelium. It will not work to vasodilate in vitro in an isolated blood vessel.
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 in patients with coronary artery disease 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 usually prescribed in combination with a beta-blocker (e.g., propranolol) and a diuretic. In the UK, labetalol tends to be the first line beta-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.
Multiple sclerosis: Due to its ability to damage myelin nerve sheaths, acrolein may be a factor in the development of multiple sclerosis. Hydralazine, a known scavenger of acrolein, was found to reduce myelin damage and significantly improve behavioral outcomes in a mouse model of multiple sclerosis (experimental autoimmune encephalomyelitis).
Common side-effects include:
- Compensatory tachycardia due to baroreceptor reflex ->Angina
- Loss of appetite
- Nausea or vomiting
- Pounding heartbeat
- Vitamin B6 deficiency 
- Drug-Induced Lupus Erythematosus
- ANCA-associated Vasculitis - Generally MPO-ANCA positive
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. Hydralazine is differentially acetylated by fast and slow acetylator phenotypes, hence incidence of lupus-like disease in slow acetylators. Rarely, hydralazine may cause Dyscrasia typically manifested as a type of leukopenia. As such, your physician may request you undergo regular Complete blood count tests.
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