Antiemetic — 5HT3 antagonist OralIM
Ondansetron
Ondansetron
CPG Reference
Ondansetron
Indications
- ✓ Moderate to severe nausea
- ✓ Active vomiting
- ✓ Nausea and vomiting prophylaxis for eye and spinal injuries
Contraindications
- ✕ Hypersensitivity to ondansetron
- ✕ Treatment with apomorphine: risk of severe hypotension and loss of consciousness
- ✕ Paediatrics less than 2 years old
Precautions
- ⚠ Serotonin Syndrome: risk in concomitant use of other serotonergic drugs (e.g. SSRIs and SNRIs)
- ⚠ Hepatic impairment: reduces clearance and prolongs half-life
- ⚠ Phenylketonuria: wafers contain aspartame, administer with caution
- ⚠ Pregnancy, first trimester: not recommended, seek advice from CSPSCC/STORC
- ⚠ Children with gastroenteritis with diarrhoea as the prominent symptom: ondansetron may worsen diarrhoea
- ⚠ ECG monitoring may be required for IV administration of high or repeated doses in patients with prolonged QT or risk factors for QT interval prolongation
- ⚠ Rapid injection may cause dizziness and transient visual disturbances
- ⚠ Look alike, sound alike (LASA) medication: Olanzapine orally disintegrating tablet
Dosing
Adult — oral wafer
Amount 4 mg oral wafer
Route Oral
Repeat Second dose may be given after 15 minutes if patient remains symptomatic
Max dose 8 mg within an 8-hour period
Oral wafer only
Paediatric (>4 years or >15 kg) — oral wafer
Amount 4 mg oral wafer
Route Oral
Repeat Single dose — not repeated
Max dose 4 mg single dose
Oral wafer only. Paediatric dose applies to >4 years or >15 kg
Adult — IM injection
Amount 4 mg IM injection
Route IM
Repeat Can be repeated once if patient remains symptomatic after 15 minutes
Max dose No further doses within 8 hours of second dose
Onset 10–15 minutes
Paediatric (>2 years) — IM injection
Amount 0.1 mg/kg up to 4 mg
Route IM
Repeat Single dose — not repeated within 8 hours
Max dose 4 mg single dose
Onset 10–15 minutes
Onset: Oral: 15–30 minutes; IM: 10–15 minutes
Side Effects & Notes
Side Effects
- • Constipation
- • Headache
- • Dizziness
- • Blurred vision (transient visual disturbance with rapid IV administration)
- • Flushing
Drug Interactions
- ⚠ Apomorphine: risk of severe hypotension and loss of consciousness — contraindicated
- ⚠ Serotonergic drugs (e.g. SSRIs, SNRIs): risk of Serotonin Syndrome
Clinical Notes
- → EHS scope is limited to oral wafer and IM injection only. IV/IO administration is outside EHS scope of practice.
- → Oral wafer paediatric dose applies to patients >4 years or >15 kg.
- → Ondansetron is authorised for EHS for nausea and vomiting prophylaxis in eye and spinal injuries.
- → Preparation for IM/IV: dilute 4 mg (2 mL) in 8 mL sodium chloride 0.9% to produce 0.4 mg/mL solution — IV route not within EHS scope.
- → LASA risk: check packaging carefully — ondansetron wafer and olanzapine orally disintegrating tablet appear similar.