Serotonin Syndrome from 5-Hydroxytryptophan Supplement Ingestion in a 9-Month-Old Labrador Retriever.

INTRODUCTION: 5-Hydroxytryptophan (5-HTP) supplements are available over the counter and labeled as sleeping aids and anxiolytics for human use. 5-HTP is a serotonin precursor and overdose can lead to serotonin syndrome. CASE REPORT: A 9-month-old female Labrador retriever was evaluated after ingestion of a 5-HTP supplement. Signs of agitation developed within 1 h of ingestion, and emesis was attempted by the owner with  3% hydrogen peroxide (H2O2) orally. On presentation, the dog was obtunded, bilaterally mydriatic and salivating. Physical exam revealed tachypnea, tachycardia, hyperthermia, and hypertension. Eighteen hours post presentation, the dog developed melena, hematemesis, and pigmenturia. A hemogram revealed mild anemia with evidence of oxidative erythrocyte damage (eccentrocytes, Heinz bodies, and siderocytes). A chemistry panel revealed markedly elevated creatine kinase and hyperbilirubinemia, supporting hemolytic anemia. A urinalysis revealed pigmenturia. Hemolytic anemia was presumed to be caused by oxidative damage secondary to gastrointestinal ulceration and circulatory embolism of H2O2. Treatment included fluid therapy, a mannitol constant rate infusion, antiemetics, gastroprotectants, and cyproheptadine as a serotonin antagonist. The patient responded well to treatment and was discharged within 48 h of presentation. DISCUSSION: Serotonin syndrome is an increasingly common toxic syndrome in veterinary medicine with the availability of over-the-counter medications that alter serotonin metabolism. The importance of appropriate client education regarding emesis with H2O2 is highlighted.