Ondansetron

5HT3 Antagonist·Gastrointestinal - Antiemetics

Chemo/radiotherapy induced nausea, post-operative nausea, severe gastroenteritis

Authority requiredPBSANTIEMETICZofran, Zydis (wafers)4 mg tablet+2

Max Dose

32 mg/day

Half-life

3-4 h

QTc Risk

HIGH

Constipation

SEVERE

Rapid Summary

Overview

Highly potent, central and peripheral 5-HT3 receptor antagonist. The gold standard for chemotherapy and post-operative nausea and vomiting (PONV).

Maximum Dose

Max 32 mg/day (Max 16 mg per single IV dose to limit QTc prolongation).

Clinical Focus

Causes profound, concrete-like constipation. Co-prescribe laxatives if used for more than 24 hours.

Bottom Line

Ondansetron is the gold-standard antiemetic for chemotherapy, post-operative, and severe nausea, but prolongs QTc and causes constipation which can be significant.

Formulation & Access

Brand Names

Zofran, Zydis (wafers)

Oral Routes

Tablets (4 mg, 8 mg). Wafers/ODT (4 mg, 8 mg) — excellent for actively vomiting patients.

Parenteral

Ampoules (4 mg/2 mL, 8 mg/4 mL) for IV / IM.

Prescribing & PBS

Authority Required (PBS) for specific chemotherapy/radiotherapy/PONV indications.

Indications & Use

Primary

PBSTGA

Chemo/radiotherapy induced nausea, post-operative nausea, severe gastroenteritis.

Clinical Place

The most effective, non-sedating, non-EPSE antiemetic on the ward. Preferred over Maxolon in bowel obstruction.

Quick reference

Class & Role

5HT3 Antagonist — Highly potent, central and peripheral 5-HT3 receptor antagonist.

Route / Formulation

Tablets (4 mg, 8 mg). Wafers/ODT (4 mg, 8 mg) — excellent for actively vomiting patients. (Zofran, Zydis (wafers))

Usual Dose & Max

PO / IV 4-8 mg BD or TDS. Max 32 mg/day.

Key Indication Doses

Nausea / Vomiting (General): PO / IV 4-8 mg BD or TDS. Max 32 mg/day. Chemotherapy Nausea: PO / IV 8 mg 1-2 hours before therapy, then 8 mg BD. Hepatic Impairment: Max 8 mg/day in severe Hepatic impairment.

Best Uses

Ondansetron is the gold-standard antiemetic for chemotherapy, post-operative, and severe nausea, but prolongs QTc and causes constipation which can be significant.

Avoid / Cautions

Co-administration with Apomorphine. Congenital Long QT syndrome. Pregnancy Category B1. Small absolute risk of oral clefts if used in 1st trimester; generally safe later.

Key Risks

Gastrointestinal: Severe constipation, bowel impaction. Cardiovascular: QTc prolongation, potentially leading to Torsades de Pointes (especially with rapid IV bolus). Neurological: Headache (very common, up to 20%), dizziness.

Key Interactions

Other QTc prolonging drugs (Amiodarone, Haloperidol, SSRIs, Macrolides). Serotonergic drugs. Very rare risk of serotonin syndrome.

Monitoring

Baseline ECG if giving IV or if the patient is on other QTc prolonging meds. Monitor bowel movements. Prophylactic laxatives (Movicol) are heavily advised.

Clinical Pearl

Ondansetron shuts down gut motility (via 5HT3 blockade). If you give this to an opioid-dependent post-op patient without a laxative, they will develop a severe bowel impaction.

Access

Authority requiredZofran, Zydis (wafers)4 mg tablet

Brand: Zofran, Zydis (wafers)
PBS status: Authority required
Formulation: Tablets (4 mg, 8 mg)

Ondansetron

5HT3 Antagonist·Gastrointestinal - Antiemetics

Chemo/radiotherapy induced nausea, post-operative nausea, severe gastroenteritis

Authority requiredPBSANTIEMETICZofran, Zydis (wafers)4 mg tablet+2

Max Dose

32 mg/day

Half-life

3-4 h

QTc Risk

HIGH

Constipation

SEVERE

Rapid Summary

Overview

Highly potent, central and peripheral 5-HT3 receptor antagonist. The gold standard for chemotherapy and post-operative nausea and vomiting (PONV).

Maximum Dose

Max 32 mg/day (Max 16 mg per single IV dose to limit QTc prolongation).

Clinical Focus

Causes profound, concrete-like constipation. Co-prescribe laxatives if used for more than 24 hours.

Bottom Line

Ondansetron is the gold-standard antiemetic for chemotherapy, post-operative, and severe nausea, but prolongs QTc and causes constipation which can be significant.

Formulation & Access

Brand Names

Zofran, Zydis (wafers)

Oral Routes

Tablets (4 mg, 8 mg). Wafers/ODT (4 mg, 8 mg) — excellent for actively vomiting patients.

Parenteral

Ampoules (4 mg/2 mL, 8 mg/4 mL) for IV / IM.

Prescribing & PBS

Authority Required (PBS) for specific chemotherapy/radiotherapy/PONV indications.

Indications & Use

Primary

PBSTGA

Chemo/radiotherapy induced nausea, post-operative nausea, severe gastroenteritis.

Clinical Place

The most effective, non-sedating, non-EPSE antiemetic on the ward. Preferred over Maxolon in bowel obstruction.

Quick reference

Class & Role

5HT3 Antagonist — Highly potent, central and peripheral 5-HT3 receptor antagonist.

Route / Formulation

Tablets (4 mg, 8 mg). Wafers/ODT (4 mg, 8 mg) — excellent for actively vomiting patients. (Zofran, Zydis (wafers))

Usual Dose & Max

PO / IV 4-8 mg BD or TDS. Max 32 mg/day.

Key Indication Doses

Best Uses

Ondansetron is the gold-standard antiemetic for chemotherapy, post-operative, and severe nausea, but prolongs QTc and causes constipation which can be significant.

Avoid / Cautions

Co-administration with Apomorphine. Congenital Long QT syndrome. Pregnancy Category B1. Small absolute risk of oral clefts if used in 1st trimester; generally safe later.

Key Risks

Key Interactions

Other QTc prolonging drugs (Amiodarone, Haloperidol, SSRIs, Macrolides). Serotonergic drugs. Very rare risk of serotonin syndrome.

Monitoring

Baseline ECG if giving IV or if the patient is on other QTc prolonging meds. Monitor bowel movements. Prophylactic laxatives (Movicol) are heavily advised.

Clinical Pearl

Ondansetron shuts down gut motility (via 5HT3 blockade). If you give this to an opioid-dependent post-op patient without a laxative, they will develop a severe bowel impaction.

Access

Authority requiredZofran, Zydis (wafers)4 mg tablet

Brand: Zofran, Zydis (wafers)
PBS status: Authority required
Formulation: Tablets (4 mg, 8 mg)