Hypertensive crisis and myocardial infarction following massive clonidine overdose.

Objective: To describe a patient who experienced a hypertensive crisis and myocardial infarction following a massive dose of parenteral clonidine.

Case Summary: A 62-year-old white woman with stage 3 breast cancer metastatic to the spine and a history of hypertension received a combined injection of hydromorphone 48.3 mg and clonidine 12.24 mg subcutaneously in an attempt to refill an implanted epidural infusion pump. She promptly developed mental deterioration, blurred vision, worsening respiration, tachycardia, and hypertension. She was immediately treated with naloxone, but subsequently experienced hypertensive urgency, a short-duration tonic-clonic seizure, and an anteroseptal myocardial infarction. Cardiac catheterization showed no arteriolar narrowing or blockage, but an anterior infarct was confirmed.

Discussion: Clonidine is a commonly used alpha-adrenergic agonist. At usual oral doses of 0.2-2 mg/d, it acts centrally to produce hypotensive effects; at doses >7 mg/d, it acts peripherally to stimulate alpha1- and alpha2-adrenergic receptors, leading to vasoconstriction and increased blood pressure. These effects are not easy to control by standard medical therapies and can cause significant morbidity.

Conclusions: Clonidine, although a safe medication with usual dosages, must be used with caution when given in injectable form. An overdose of this alpha-adrenoreceptor agonist can produce significant vasospasm and hypertensive emergency. Drugs used to treat overdose, such as naloxone, can potentiate clonidine's adverse effects, leading to further morbidity.