What is the recommended antiemetic for nausea/vomiting after pain medications?

• A. Ondansetron 4 mg ODT/IM/IV/IO
• B. Promethazine
• C. Metoclopramide
• D. Prochlorperazine

Answer: (A)

Ondansetron is the best choice because it works by blocking serotonin 5-HT3 receptors both in the gut and in the vomiting center of the brain, which effectively counters nausea and vomiting that can occur after opioids. It tends to have a rapid onset and a favorable safety profile, with minimal sedation and a low risk of extrapyramidal symptoms, making it well suited for prehospital use where many patients need to stay alert and able to participate in care.

Promethazine, while an antiemetic, often causes significant sedation and anticholinergic effects. It can also cause dangerous tissue injury if given IV and has a higher risk of extrapyramidal symptoms compared with ondansetron. Metoclopramide and prochlorperazine are dopamine antagonists; they can be effective but carry a higher risk of extrapyramidal reactions (like dystonias), sedation, and, in some cases, QT prolongation. These downsides make them less desirable in the scene where rapid, safe relief is preferred after pain medication administration.