Blood pressure crisis following withdrawal of clonidine (Catapres, Catapresan), with special reference to arterial and urinary catecholamine levels, and suggestions for acute management.

C lonidine is an imidazoline derivative with antihypertensive properties. Its mode of action is complex and is as yet not fully understood. Some datal-‘j indicate that an action on the central nervous system, predominantly at bulbar and diencephalic levels, causes a decreased sympathetic outflow to the cardiovascular system. Other studies’ show a direct peripheral effect as well. Since the introduction of clonidine in Europe in the mid-sixties, several reports have been published regarding its usefulness in the treatment of hypertension.8-12 Without trying to evaluate the advantages or disadvantages of clonidine treatment in relation to those of other antihypertensive drugs, it is of utmost importance to be aware of the effects which may follow abrupt cessation of treatment, and which presumably reflect an adrenergic overshoot. There have been some previous attempts to draw attention to the clonidine withdrawal crisis,13*14 but on the whole this is a poorly studied phenomenon. The present study is a description of the blood pressure overshoot and the typical symptoms that are seen when clonidine is stopped abruptly. Attempts have also been made to clarify the underlying mechanism by means of catecholamine determinations in urine and arterial blood before and during the crisis. Finally, suggestions are offered for the acute management of the crisis as well as a possible way to prevent it from occurring.