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.