Hydralazine
Hydralazine is not preferred for hypertensive emergencies due to the high risk of reflex sympathetic stimulation.
| Drug | Hydralazine |
| Brand names | Apresoline ®, Bidil ® |
| Mechanism of action | • Induces arteriolar vasodilation. No effect on venous circulation. • May cause reflex sympathetic stimulation (can be counteracted with simultaneous administration of beta-blockers). |
| Effects | Induces arteriolar vasodilation without effects on venous circulation. The reduction in systemic vascular resistance (SVR) is rapid and may cause reflex sympathetic stimulation, including tachycardia. May therefore induce or worsen angina pectoris. The rapid reduction of afterload is desired in conditions requiring afterload reduction. |
| Time to onset of action | 10-30 minutes. |
| Duration of action | <4 hours. |
| Delivery | IV or IM. |
| Dose | Injections • IV: 10–40 mg every 4–6 hours • IM: 10–20 mg every 4–6 hours. Infusion • Afterload reduction: Start infusion at 1 mg/hour. Increase by 0.5 mg/hour every 20 min to desired blood pressure. Maximum infusion rate 5 mg/hour. • Antihypertensive treatment: Start infusion at 5 mg/hour. Increase by 2.5 mg/hour every 20 min to desired blood pressure. Maximum infusion rate 25 mg/hour. |
| Adverse effects | Tachycardia. Flushing. Headache. Angina pectoris. |
| Caution | Heart failure. Angina pectoris (ischemic heart disease). |