Hypersensitivity to intravenous ondansetron: a case report.

INTRODUCTION: Ondansetron, a 5-hydroxytryptamine3 receptor antagonist widely used in the prevention and treatment of chemotherapy-induced nausea and vomiting, is associated with various unusual adverse drug reactions. In this paper, we describe a hypersensitivity reaction to a single intravenous dose of ondansetron.

CASE PRESENTATION: A 19-year-old woman presented to the emergency department of our institute with 3-4 episodes of nausea, vomiting and epigastric distress. She had a diagnosis of polycystic ovarian disease and had been on treatment with cyproterone acetate 2 mg, ethinyl estradiol 0.035 mg, finasteride 5 mg and metformin 500 mg for a month. She had been taking oral roxithromycin 500 mg per day for the past 3 days for treatment of a mild upper respiratory tract infection. She also occasionally took rabeprazole 10 mg for gastritis which had worsened after treatment with roxithromycin. She was treated with a single 4 mg dose of ondansetron intravenously. She immediately developed urticaria, which was treated with intravenous dexamethasone 4 mg and chlorpheniramine maleate 20 mg. The reaction abated within a few minutes and she was discharged within an hour. She was asymptomatic at 72 hours of follow-up.She had no history of ondansetron exposure, or drug or food allergies. On the Naranjo's causality assessment scale, the adverse event was 6 indicating a "probable" reaction to ondansetron.

CONCLUSION: 5-hydroxytryptamine3 receptor antagonists have been associated with life-threatening adverse reactions such as hypotension, seizures and anaphylaxis. The wide availability of these drugs in India has promoted their off label use in the treatment of gastritis, migraine and so on. Our case represents an off label use in a patient who could have been treated with a safer drug.Some authors have suggested that anaphylaxis may be a class effect while others think it may be drug specific. In our case, the reaction could be either anaphylaxis or anaphylactoid, but the latter seems more likely given the history of absence of prior sensitization. Other components of the drug, such as solvent, also need to be considered as a cause of this reaction. Considering all of the existing evidence, we need to be more cautious while using ondansetron and also to be aware of the various unusual side effects, especially when used in an out-of-hospital set-up.Our case report underscores the importance of physicians judiciously using the drug, particularly in the outpatient setting so as to reduce the incidence of avoidable adverse drug reactions.