Guanfacine overdose resulting in initial hypertension and subsequent delayed, persistent orthostatic hypotension

Guanfacine is an alpha(2)-adrenoreceptor agonist used for the treatment of attention-deficit hyperactivity disorder and tic disorders. Few reports exist regarding overdose with guanfacine.

A 16-year-old female with Tourette's syndrome presented with diaphoresis, dry mouth, and hypertension 8 h after ingesting 25 mg of guanfacine. These symptoms improved and her blood pressure (BP) normalized over 2 h. Thirty hours following ingestion, she experienced near syncope and returned to the emergency department. She was noted to have orthostatic hypotension and a prolonged QTc interval of 593 ms on electrocardiogram. With only fluid support, she was asymptomatic by 60 h postingestion and her QTc interval had improved to 511 ms.

This experience suggests a much delayed onset of symptoms may occur and that the QTc interval may be prolonged, necessitating a longer period of monitoring in a patient presenting with an overdose.