Ondansetron
Class: antiemetic – specific 5HT 3 antagonist
Indications (NB some may be unlicensed): nausea/vomiting post chemo- or radio- therapy, post-operative nausea/vomiting, nausea/vomiting not due to above including acute severe vomiting
Contraindications/cautions: contraindicated in congenital prolonged QT; caution with other QT prolonging drugs & serotonergic drugs, caution in hepatic impairment (max dose 8 mg daily), subacute gastro-intestinal obstruction
Adverse reactions: common: headache, flushing, constipation; less common: hiccups, hypotension, injection site reaction, dizziness, cardiac effects (iv usually tachycardia, chest pain, arrhythmias); rarely: QT prolongation (Torsade de Pointes)
Metabolism/clearance: metabolised by metabolising enzyme CYP2D6 mainly in the liver
Interactions:
- increased clinical effect/toxicity of ondansetron (due to increased blood concentrations) may occur with some CYP metabolising enzyme inhibitors (see above) e.g. bupropion, fluoxetine, paroxetine, quinine
- QT prolongation risk with domperidone (contraindicated together in UK) and other QT drugs (NZF)
| Dosing: | |
|---|---|
| oral: | 4 to 8 mg twice a day |
| subcut: | not usually used |
| rectal: | not available |
Syringe driver: see syringe driver compatibility chart
Mechanism of action: Ondansetron reduces the vomiting reflex by blocking serotonin at 5HT 3 receptors both peripherally in the GI tract and centrally in the CTZ
Peak concentration: oral: 1 to 2 hours im (subcut): 30 minutes
Notes:
- may be of use in nausea and vomiting refractory to all other antiemetics
- available as an oro-dispersable tablet – place on top of tongue and allow to dissolve before swallowing
- 0.8 mg/mL oral suspension can be prepared