The antihypertensive drug clonidine has a double and antagonistic effect on arterial blood pressure. As a result of activation of peripheral α-adrenergic receptors, it causes a transient increase in blood pressure; by a central action it decreases sympathetic tone which results in sustained bradycardia and hypotension. Both central and peripheral effects are experimentally blocked by tolazoline, an α-adrenergic blocking agent. The toxic symptoms seen in clonidine poisoning are usually produced by the central effect. A case of severe clonidine poisoning in a 9-month-old infant is reported. The clinical picture included coma, miosis, apneic spells, bradycardia, and hypertension. Rapid and complete recovery was obtained with supportive treatment that included assisted ventilation. No adrenergic blockers or antihypertensive drugs were given. Use of tolazoline in cases of clonidine overdose in children remains controversial. Supportive measures alone may be adequate for even the most severe cases.
Clonidine poisoning in a toddler