Guanfacine: effects of long-term treatment and withdrawal

1. Guanfacine 3-6 mg daily lowered blood pressure in five essential hypertensives and also reduced saliva production. 2. Plasma and urinary noradrenaline values were significantly reduced throughout the 8-10 weeks of treatment. 3. On substitution of placebo tablets for guanfacine, blood pressure increased over a 2-4 d period to reach but did not significantly exceed pretreatment levels. 4. After withdrawal of guanfacine plasma noradrenaline standing was significantly higher than the pretreatment level (P < 0.05) after 4 days. Saliva production was significantly higher than the pretreatment level on day 3 and day 4 of withdrawal. 5. Guanfacine is an effective antihypertensive drug with a spectrum of actions similar to clonidine. However, in abrupt withdrawal blood pressure returned to the pretreatment level over a 2-4 d period.