Life-threatening altered mental status secondary to memantine in an adolescent undergoing cranial radiotherapy for medulloblastoma

Introduction Memantine is used for neurocognitive protection in patients undergoing cranial radiotherapy for central nervous system tumors and is reported to be well-tolerated. Case report Presented is a case of memantine-induced altered mental status requiring an intensive care unit admission. An 18-year-old male with relapsed, progressive medulloblastoma presented with severe altered mental status shortly after the first fraction of palliative whole brain radiotherapy. At the time, the patient was on day five of memantine therapy, which had been prescribed to reduce neurocognitive toxicity risk. Management & outcome Memantine was withheld while dexamethasone, valproate, and morphine were continued for headache. Approximately 50 h after admission, the patient's confusion significantly improved. Evaluation of acute altered mental status was unrevealing, including but not limited to negative urinary toxicology screen and lack of disease progression on imaging. Whole brain radiotherapy was resumed after a two-day cessation and he was discharged home after four days with complete resolution of symptoms. Discussion Clinicians should be aware of and consider the risk of altered mental status with memantine, given the increased utilization and upcoming clinical trials in pediatric patients.