Ondansetron (Zofran)

Anesthesia Implications

Classification: Selective serotonin receptor (5-HT3) antagonist
Therapeutic Effects: PONV prophylaxis, Reducing Spinal anesthesia induced hypotension
Time to Onset: < 30 minutes
Time to Peak: Variable
Duration: 12-24 hours

Primary Considerations

Slow Push – The most common side effect of this drug is a headache, which has been associated with a rapid bolus. Ideally, Zofran should be given over 2-5 minutes. In any case, Zofran should NOT be given over less than 30 seconds.

Coadministration – Zofran by itself will reduce PONV by up to 33%. Coadministration of dexamethasone (Decadron) or methylprednisolone will have additive affects.

OB – Zofran DOES cross the placenta AND also into breast milk. Use with caution in the parturient and breastfeeding mothers.

Dysrhythmias – Zofran can cause dysrhythmias, specifically when combined with metoclopramide.

Tramadol – Ondansetron reduces the analgesic affects of tramadol.

IV push dose

Adult and pediatric PONV prophylaxis: 0.10 – 0.15 mg/kg
Reducing Spinal anesthesia induced hypotension: 4-8 mg IV just prior to LA in the intrathecal space

Method of Action

Serotonin (5-HT3) receptors can be found peripherally on vagal nerves as well as centrally in the chemoreceptor trigger zone (CTZ). Zofran is a serotonin antagonist at both of these sites, which helps to eliminate/reduce the emetic effects that serotonin would produce.

Zofran is also useful to treat spinal anesthesia induced hypotension.  In this case, ondansetron is believed to inhibit the reflexive drop in heart rate as a result of spinal anesthesia (otherwise known as the Benzold-Jarisch reflex)

Metabolism

Hepatic

Additional Notes
Some studies show that Zofran is more effective at preventing vomiting versus nausea.