To the Editor.—
The wide variety of antihypertensive agents now available to the physician has complicated therapy and increased the potential for unexpected drug interactions. We describe briefly two patients in whom the combination of propranolol hydrochloride and clonidine hydrochloride produced a paradoxical hypertensive response.
A 61-year-old man had poorly controlled essential hypertension (blood pressures, 160/95 to 210/95 mm Hg) while receiving hydrochlorothiazide, 50 mg twice a day, and methyldopa, 500 mg three times a day. The addition of clonidine hydrochloride, 0.2 mg twice daily, lowered blood pressure to 160/60 mm Hg. Subsequently, the patient was found to have idiopathic hypertrophic subaortic stenosis; propranolol hydrochloride, 40 mg twice a day, was added. One week later, blood pressures were 260/100 to 270/120 mm Hg. Propranolol dosage was increased and clonidine discontinued, resulting in a gradual decline of blood pressure to 160/70 mm Hg.
The essential hypertension of