Ondansetron (Zofran) is a common oral and IV medication I use for post-operative nausea/vomiting prophylaxis. It works by antagonizing serotonergic (5-HT3) receptors located in peripheral vagal terminals and in the medulla’s area postrema within the chemoreceptor trigger zone (same place propofol works as an anti-emetic).

The FDA warnings regarding QTc prolongation from ondansetron studied intravenous doses of 32 mg. Although I only give 4-8 mg IV at a time, smaller studies have also shown QTc prolongation with these lower doses (however, the clinical significance is controversial). That being said, I’m cautious about using ondansetron in patients with preexisting long QTc (for whatever reason), arrhythmias, and severe electrolyte derangements.

Ondansetron was also found beneficial in improving the negative symptoms of schizophrenia as well as post-operative shivering – a major consideration in patients at risk for end-organ tissue hypoxia (coronary artery disease, carotid stenosis, etc.).

I’ve found ondansetron to be minimally helpful in patients who are already vomiting. This attests to ondansetron’s role in PROPHYLAXIS! In these cases, I’ll use alternatives like 1 mg IV Haldol, 6.25 mg IV promethazine or even 10-20 mg IV propofol.

Drop me a comment below with questions! 🙂

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  1. Love your summarized posts on drugs! Thank you! Could you do a post on phenergan please? Do you use it often in postop patients?


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