Clonidine hydrochloride in the treatment of hypertension.

From the Hypertension Section, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, Mich. This study was assisted by U. S. Public Health Service Grant 5MOl-FR-42 to the Clinical Research Unit, University of Michigan Medical Center, which enabled hospitalization of patients included in the study. Manuscript received December 14, 1970, accepted February 12, 1970. Address for reprints: Sibley W. Hoobler, MD, Hypertension Section, R6669 Kresge Medical Research Building, University of Michigan Medical Center, Ann Arbor, Mich. 48104. Clonidine hydrochloride (Catapres) combined with a diuretic agent was given to 57 patients for a period of 6 months to 2 years. It was shown to be an effective agent for the long-term treatment of hypertension. It acts by central inhibition of adrenergic vasomotor stimulation; its withdrawal can cause transient sympathoadrenal hyperactivity. Dry mouth, constipation and transitory drowsiness were the most common side effects. They diminished with time, even when the dose was progressively increased. Bradycardia was produced by inhibition of cardiac sympathetic innervation, but no serious dysrhythmias occurred. The drug can be used to advantage as a replacement for guanethidine or methyldopa (Aldomet) but must be given with a diuretic agent. Orthostatic hypotension was rare. Addition of hydralazine or reserpine in conventional dosage decreased blood pressure very moderately. No change was observed when alpha methyldopa was added. On the contrary, administration of clonidine to a patient exhibiting partial adrenergic blockade with guanethidine augmented the effects of such blockade, causing a further decline in both standing and recumbent blood pressure. This 3 year experience shows that clonidine is safe and free from toxicity. It is effective if patiently administered in increasing dosage until proper control of blood pressure is achieved.