Reversal of clonidine toxicity by naloxone.

Clonidine is a centrally acting antihypertensive agent used in the management of essential hypertension. Oral clonidine loading is now used frequently in the management of hypertensive urgencies (ie, increases in arterial pressure not associated with acute, life-threatening end-organ injury). We report the case of a patient with an acute inferior myocardial infarction associated with blunt chest trauma who developed an abrupt and unexplained increase in arterial pressure 24 hours after admission and who was treated with oral clonidine (0.5 mg in divided doses over two hours). Drug therapy was followed by prolonged (four hours) systemic arterial hypotension (mean arterial pressure less than 70 mm Hg). Four milligrams of naloxone in two divided doses was given. Each naloxone bolus was followed by a 15-mm-Hg increase in mean arterial pressure and a return to values that were normal for this patient. Naloxone may be of value in reversing clonidine toxicity when clonidine is given to treat an acute rise in arterial pressure.