Selective Serotonin Receptor (5‐HT3) Antagonist Prescribing in Cancer Inpatients: A Retrospective Clinical Audit

AIM: Selective serotonin receptor (5-HT3) antagonists are first-line antiemetics for chemotherapy-induced, radiotherapy-induced, and post-operative nausea and vomiting; other causes of nausea in advanced cancer warrant alternative agents. We aimed to determine patterns of inpatient 5-HT3 antagonist prescribing and its guideline concordance. METHODS: We retrospectively reviewed electronic medical records of all patients admitted under Medical Oncology at a single metropolitan hospital over 6 months who were prescribed a 5-HT3 antagonist. Data on demographics, cancer, and the prescription (agent, indication, prescriber, duration, administration) were extracted and reviewed for guideline concordance. Analyses were descriptive. RESULTS: Of 210 patients admitted between January and June 2025, 81 (38.6%) were prescribed a 5-HT3 antagonist. Mean age was 64.2 years (range 24-87); 41 (50.6%) were female, and 62 (76.5%) had metastatic cancer. Of 137 prescriptions written, 134 (97.8%) were for ondansetron. Nausea was documented in 104 (75.9%), but a specific cause in only 55/104 (52.9%). The most common prescribers were Emergency (62, 45.3%) and After-Hours (32, 23.4%) doctors. Prescriptions were brief (median 1 day); 82 (59.9%) were administered at least once, and 62/82 (75.6%) were single-dose. Overall, 93 (67.9%) were non-concordant. Concordance was 10/14 (71.4%) in Medical Oncology, 20/21 (95.2%) in anesthetics and intensive care, 4/4 (100%) in Radiation Oncology, and 4/4 (100%) in Palliative Care, but 2/62 (3.2%) in Emergency and 4/32 (12.5%) in After-Hours prescribers. CONCLUSION: 5-HT3 antagonists were frequently prescribed outside guideline recommendations, particularly by clinicians less familiar with cancer. Targeted education, electronic order-set redesign, and structured documentation of the suspected mechanism of nausea may improve guideline-concordant antiemetic prescribing.