Paediatric Antiemetics

Vomiting in children is mostly caused by gastroenteritis, and the priority is fluid replacement and treatment of the cause, not an antiemetic. Antiemetics are used for persistent vomiting that blocks oral rehydration, postoperative vomiting and chemotherapy.

Red flags that need investigation, not antiemetics. Bilious or bloody vomit, abdominal distension, projectile vomiting at 2 to 8 weeks (pyloric stenosis), severe headache, head injury, diabetic ketoacidosis, raised intracranial pressure, and signs of obstruction.

• Ondansetron (first line): 0.1 to 0.15 mg/kg orally or intravenously, maximum 4 mg for a single dose. Fixed single oral doses in gastroenteritis: 2 mg for 8 to 15 kg, 4 mg for 15 to 30 kg, 6 mg over 30 kg. Repeat every 8 hours if needed, to a maximum of 3 doses in 24 hours. Start oral rehydration solution 15 to 30 minutes after the dose.
• Postoperative nausea and vomiting: ondansetron 0.1 mg/kg intravenously (maximum 4 mg) with dexamethasone 0.15 mg/kg (maximum 8 mg).
• Chemotherapy: ondansetron with dexamethasone, and aprepitant for highly emetogenic regimens under oncology direction.
• Cyclizine (motion or vestibular causes): 1 mg/kg orally every 8 hours (maximum 50 mg a dose), avoid under 1 year.
• Metoclopramide: avoid in infants and children, because of oculogyric crisis and extrapyramidal effects; if used, 0.1 mg/kg (maximum 5 mg) for no more than 5 days, and never under 1 year.
• Promethazine: avoid under 2 years (respiratory depression); not advised for routine use.
• Domperidone: avoid for routine use.

QT prolongation. Ondansetron prolongs the QT interval. Avoid with congenital long QT, hypokalaemia, hypomagnesaemia, and other QT-prolonging drugs (macrolides, antipsychotics, fluconazole). Correct electrolytes first.

Liver impairment. Limit ondansetron to a maximum of 8 mg daily in severe hepatic impairment.

Kidney impairment. No dose adjustment for ondansetron.

Constipation. Ondansetron can cause constipation and headache.

Special groups. Pregnant adolescents need review of vomiting in context, and ondansetron is used with caution in the first trimester. In East Africa, ondansetron orally disintegrating tablets are the most available option, and dehydration is corrected with oral rehydration solution first.

Monitoring. Check hydration, ability to drink, urine output, and for ongoing vomiting after 30 to 60 minutes. Record ECG when giving repeated intravenous doses to a child with cardiac risk.

Referral and escalation. Escalate for failure of oral rehydration after one dose, bilious vomiting, abdominal tenderness, neurological signs, signs of dehydration despite treatment, and suspected diabetic ketoacidosis.

Stopping. Stop when the child is tolerating oral fluids. Do not continue beyond 24 to 48 hours in gastroenteritis.