title: Withdrawal of guanfacine after long-term treatment in essential hypertension. Observations on blood pressure and plasma and urinary noradrenaline.
abstract: 1. Guanfacine (2-6 mg/day) a centrally acting antihypertensive drug, was effective in controlling blood pressure in 5 essential hypertensives and lowered plasma noradrenaline and urinary catecholamine excretion. 2. Withdrawal of guanfacine by blind substitution of identical placebo tablets under observation in hospital led to a gradual recovery of blood pressure over 2-4 days. 3. Salivary flow, which was reduced on guanfacine, returned to pretreatment levels by 2 days after withdrawal and significantly exceeded control for the next two days. 4. Urinary catecholamine excretion returned to pretreatment levels by 3 days but did not exceed control levels during the period of study. 5. Plasma noradrenaline returned gradually to pretreatment levels, and by day 4 significantly exceeded them. 6. No patient experienced symptoms suggesting catecholamine excess although four out of five reported a headache from the second day onwards. 7. Guanfacine, a centrally acting drug which pharmacologically resembles clonidine, has a slow offset of hypotensive effect over 2-3 days. Symptoms or biochemical evidence of catecholamine excess were not encountered within 48 h of withdrawal, possibly reflecting the longer duration of action and plasma half-life of guanfacine.
mesh_terms: D001794:Blood Pressure / Q000187:drug effects*; D005260:Female; D016316:Guanfacine; D006146:Guanidines / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D006973:Hypertension / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000378:metabolism*; D010648:Phenylacetates / Q000494:pharmacology / Q000627:therapeutic use*; D011187:Posture; D012463:Saliva / Q000187:drug effects; D013375:Substance Withdrawal Syndrome
chemical_list: D006146:Guanidines; D010648:Phenylacetates; D016316:Guanfacine; D009638:Norepinephrine