Pharmacology

Hydralazine

Hydralazine (Apresoline) is an intravenous and oral antihypertensive which promotes the direct relaxation of arterioles through an unclear mechanism potentially involving calcium flux within the vascular smooth muscle. By acting primarily as a vasodilator (compared to venodilator), peripheral vascular resistance decreases causing the diastolic blood pressure to drop more than the systolic with a concurrent augmentation in stroke volume, heart rate, and therefore overall cardiac output.

This cardiac sympathetic response coupled with an increase in the renin-angiotensin-aldosterone pathway can lead to increased myocardial ischemia in high risk patients and fluid retention, respectively. For this reason, patients on long term hydralazine tend to be on some combination of beta-blocker and diuretic therapy.

Although hydralazine is considered a safe option for hypertension in pregnancy, it can produce a drug-induced lupus-like state in any patient. As an intensivist and anesthesiologist, I prefer other antihypertensive agents since hydralazine’s pharmacokinetics vary tremendously due to polymorphic acetylation metabolism. In certain patients it works great, in other patients it doesn’t seem to work at all, and in most patients, the onset of action is > 10 minutes.

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