Withdrawal phenomena in subjects with essential hypertension on clonidine or tiamenidine.

The incidence and pathogenesis of withdrawal phenomena with the centrally acting drugs clonidine (CLON) and tiamenidine (TIAM) were evaluated. Thirty subjects with hypertension on hydrochlorothiazide (HCTZ) were randomized to TIAM or CLON. Blood pressure and integrated plasma catecholamine levels fell equally in response to both drugs. On withdrawal, blood pressure and pulse rose in both groups with no difference between them. Three subjects had symptoms of withdrawal, four had blood pressure overshoot above pretreatment levels of 10 mm Hg or more, and eight had a rise in blood pressure of 30 mm Hg systolic or 20 mm Hg diastolic. There was no difference between TIAM and CLON in these effects. There was a direct correlation between blood pressure rise and increase in integrated plasma norepinephrine levels. We conclude that the incidence of withdrawal phenomena in subjects on TIAM or CLON is infrequent and that there is a direct relationship between the rise in blood pressure and the loss of suppression of catecholamines by these drugs.