Evaluation of Intravenous Clonidine in Hypertensive Emergencies

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Abstract
Nineteen patients with severe essential hypertension or hypertension due to renal parenchymal disease were treated with i.v. clonidine. In 14 patients the elevated blood pressure was complicated by 1 or more crises: left ventricular failure in 7 patients, encephalopathy in 6, and subarachnoid hemorrhage, cerebral hemorrhage, dissecting aortic aneurysm, acute renal failure, and severe epistaxis, 1 episode each. Clonidine (0.15 or 0.30 mg) was given i.v. every 40 min until the diastolic blood pressure (BP) decreased to 120 mm Hg or below. BP was taken every 10 min. Both systolic and diastolic BP were significantly reduced after i.v. clonidine, the former by 96 mm Hg (P < 0.001), the latter by 52 mm Hg (P < 0.001) within a period of 40 min to 2 1/2 h. The clonidine dose varied 0.15-0.90 mg, mean 0.52 mg. Heart rate was decreased significantly by 20 beats/min (P < 0.001) by the drug. Serious side effects were not observed except for an episode of transient sinoatrial block. Renal function was unaffected. Patients who were on chronic diuretic therapy prior to treatment with i.v. clonidine showed a significantly greater decrease in both systolic (P < 0.01) and diastolic (P < 0.001) BP after the 1st clonidine dose. In 1 patient i.v. clonidine was ineffective (i.e., BP remained 200/150 mm Hg) in spite of a total clonidine dose of 0.9 mg. Patients (2) died, one from severe cerebral hemorrhage, the other from an extensive dissecting aortic aneurysm, but the fatal outcome was unrelated to clonidine.