Evaluation of long-term treatment of essential hypertension with guanfacine.

1. Twenty-two patients with moderately severe essential hypertension were treated for a period of 12 months with guanfacine (BS 100-141), a new centrally-acting antihypertensive agent. A twice daily schedule was followed and the dose range of guanfacine was 1-8 mg daily. 2. In twenty patients satisfactory blood pressure responses (diastolic pressure below 95 mmHg) were achieved in both the supine and the standing position. Pulse rate decreased slightly, though not significantly. 3. Tolerance to the pressure-lowering effect of the drug developed during the third or fourth month of therapy. This could be overcome by either increasing dosage or adding a diuretic. 4. All patients reported side-effects, mainly dryness of the mouth and fatigue. These side-effects became less or disappeared at the end of 3 months. Rebound hypertension on discontinuation of therapy occurred in two patients. 5. Plasma concentrations of noradrenaline and adrenaline as well as plasma renin activity were decreased after 1 week of treatment with the drug. 6. Guanfacine in conjunction with a diuretic is a useful drug in the long-term treatment of hypertension. Reduced central sympathetic outflow may be the major mechanism underlying the antihypertensive effect of the drug.