Ondansetron is a selective serotonin 5-HT₃ receptor antagonist. An intravenous formulation has been approved in the United States for the prevention of nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy. We have received 24 reports to the Spontaneous Reporting System of the Food and Drug Administration (FDA) of anaphylactoid-anaphylactic reactions in association with ondansetron injection.

Most reactions occurred after the first ondansetron dose during the second or third course of chemotherapy and were characterized by urticaria, angioedema, hypotension, bronchospasm, and dyspnea. The most serious case, reported from Belgium, involved a 62-year-old woman; before her second course of chemotherapy for ovarian carcinoma, she experienced shock with cardiac arrest and apnea 10 minutes after the administration of intravenous ondansetron and clorazepate. A lymphocyte transformation test to ondansetron showed a positive result.

These reactions may have been secondary to chemotherapy, but follow-up with persons who reported the domestic cases indicated that patients experienced no adverse events after being rechallenged with the same chemotherapeutic agents without ondansetron. This finding suggests that intravenous ondansetron was the cause. Alternatively, except when a lymphocyte transformation result was positive for ondansetron, a drug interaction between ondansetron and the chemotherapeutic agent may have occurred, possibly triggering the anaphylactoid-anaphylactic event.

Physicians and other health care professionals should report any suspected serious and unlabeled adverse drug reactions on form 1639 to the FDA's Division of Epidemiology and Surveillance.