An overdose of extended-release guanfacine.

Extended-release guanfacine is a centrally acting α2-adrenergic agonist that was recently approved for treatment of attention-deficit/hyperactivity disorder. The following is a case discussion of a 12-year-old boy with attention-deficit/hyperactivity disorder and Tourette syndrome, who presented 18 hours after ingestion of 3 times his usual dose of extended-release guanfacine. On presentation, he was lethargic, bradycardic, and hypertensive with an otherwise nonfocal neurological examination. He remained hypertensive until administration of an intravenous antihypertensive agent (nicardipine) 24 hours after ingestion. After cessation of the calcium-channel blocker, he continued to have intermittent episodes of symptomatic hypotension for the next 2½ days. This extremely protracted course of hypertension followed by prolonged symptomatic hypotension is rare with ingestions of centrally acting α2-adrenergic agonists. As this drug is increasingly prescribed for treatment of a disease with increasing prevalence, it is imperative that emergency physicians become familiar with the varying presentations of its toxicity.