Blood pressure, heart rate, catecholamines and plasma renin activity following institution and withdrawal of guanfacine treatment in moderate hypertension.

Five patients with essential hypertension of WHO grade II-III were treated with guanfacine 0.5-2 mg three times daily. They were hospitalized for 6-8d during the institution and the withdrawal of medication for the determination of blood pressure, heart rate, plasma and urinary catecholamines, and plasma renin activity (PRA) in the supine and the upright position. During the institution of medication, blood pressure became normal in four patients given 3 mg daily. Heart rate was moderately reduced. One patient needed 6 mg daily for normalization of blood pressure but, due to sedation, the dosage had to be reduced to 4 mg daily after 48 hours. After 3 weeks guanfacine was withdrawn completely in this patient because of an acute attack of mental confusion. Guanfacine caused a marked reduction in plasma noradrenaline, PRA and urinary noradrenaline excretion. Plasma adrenaline was somewhat reduced. When guanfacine was withdrawn abruptly following 4-8 weeks of medication, blood pressure, heart rate, plasma catecholamines and PRA gradually returned to pretreatment levels within 4 days. Urinary noradrenaline excretion was slightly higher, though not significantly, on day 4 after withdrawal of guanfacine than before treatment. This short study in a small number of patients supports the view that guanfacine is effective in reducing blood pressure and to some extent heart rate in hypertensive patients. The blood pressure lowering effect was closely related to a decrease of noradrenaline in plasma and urine, indicating inhibition of sympathetic activity. Guanfacine also lowered PRA. Following the abrupt cessation of treatment after 4 weeks there were no rebound phenomena with respect to blood pressure, heart rate, plasma catecholamines or PRA.