Abstracts

During initial clinical trials of ondansetron, only 10 patients ([lt]1%) had seizures. All had tumors with numerous risk factors for seizures. There are only two additional reports of seizures following ondansetron administration in humans, one in a patient with septic shock after resuscitation from cardiac arrest, and another in a patient with metastatic breast cancer on chemotherapy. In animal studies, both proconvulsant and anticonvulsant effects of ondansetron have been described. Retrospective review of three patients evaluated during the period 2004-2005. There were two females and one male. Ages ranged from 38-56 years. None had a previous or family history of seizures. Past medical history was significant only for diabetes, with one patient presenting in diabetic ketoacidosis. A generalized tonic-clonic seizure occurred in each patient 12, 15 and 22 minutes after injection of 4 mg of ondansetron intravenously for severe nausea and vomiting. Seizures were brief and patients returned to their baseline clinical state within a few minutes. Although no antiepileptic drugs were given, none had seizure recurrence subsequently. Brain MRI and EEG were normal in all patients. The temporal relationship between ondansetron administration and seizures, lack of EEG or MRI abnormalities and absence of seizure recurrence suggest that the seizures in our patients were causally related to ondansetron. Ondansetron associated seizures may be more common than previously recognized and can occur in patients with no obvious predisposing factors. Based on previous reports and our own experience, they typically present as a single generalized tonic-clonic seizure within 30 minutes of parenteral administration of ondansetron. The exact mechanism is unknown.