Ondansetron-associated hypokalemia in a 2-year-old with pre-B-cell ALL

Ondansetron is a commonly used medication in the treatment of nausea and vomiting arising from many etiologies, including chemotherapy. Although it is a highly safe drug, ondansetron use has been associated, rarely, with hypokalemia. However, it is unknown whether hypokalemia is due to the medication itself or to an underlying potassium disturbance caused by prior metabolic derangements, including vomiting. We relate a patient who presents with hypokalemia of unknown etiology, with evidence suggesting a possible relationship to ondansetron. We also present a proposed mechanism for this phenomenon.