Guanfacine intoxication in a young child presenting with prolonged somnolence and sinus bradycardia: a case report.

Guanfacine, a medication used to treat attention-deficit hyperactivity disorder (ADHD), activates alpha-2A adrenergic receptors in the brain to reduce symptoms. However, its central alpha-2 agonist activity can cause adverse events, such as somnolence, bradycardia, and hypotension. We present the case of a 6-year-old boy (15 kg) with no history of regular medication use who was admitted to the hospital with unexplained prolonged somnolence and bradycardia. Initial evaluation ruled out common causes; however, ingestion of his mother's prescription medication was suspected. Liquid chromatography-quadrupole time-of-flight mass spectrometry confirmed the presence of 6 ng/mL of guanfacine in his serum, which, together with his symptoms, led to a diagnosis of guanfacine intoxication. To our knowledge, this is the first report of guanfacine intoxication in a young child without ADHD with documented serum concentration measurements. This case may help in the recognition and diagnosis of guanfacine toxicity in pediatric patients.