What is the recommended dose of promethazine (Phenergan) for a pediatric patient over 2 years old with nausea and vomiting, according to the British National Formulary (BNF)?

Promethazine Dosing for Pediatric Nausea and Vomiting

Promethazine is contraindicated in children under 2 years of age due to fatal respiratory depression risk, and for children over 2 years, the recommended dose is 0.5 mg per pound (approximately 1.1 mg/kg) of body weight, with individual doses of 12.5-25 mg repeated every 4-6 hours as necessary. 1

Critical Safety Contraindication

• Promethazine carries a black box warning and is absolutely contraindicated in children under 2 years of age due to risk of fatal respiratory depression 2, 1
• This contraindication applies to all formulations and routes of administration 1

Dosing for Children ≥2 Years Old

Weight-Based Calculation

• The standard pediatric dose is 0.5 mg per pound of body weight (approximately 1.1 mg/kg), adjusted to the age, weight, and severity of the condition 1
• Practical dosing typically ranges from 12.5 mg to 25 mg per dose 1

Frequency and Administration

• Doses may be repeated every 4-6 hours as necessary 1
• After initiation of treatment, dosage should be adjusted to the smallest amount adequate to relieve symptoms 1

Route Considerations

• Oral administration is preferred when tolerated 1
• When oral medication cannot be tolerated, parenteral or rectal suppository routes may be used 1

Important Clinical Caveats

Respiratory Depression Risk

• Respiratory depression can occur even at recommended doses in children over 2 years 3
• One case series documented respiratory arrest in a child receiving 0.07 ml/kg of a meperidine-promethazine-chlorpromazine combination (lower than the recommended dose), with recovery requiring naloxone 3
• Frequent monitoring is essential when promethazine is administered to pediatric patients 3

Additional Adverse Effects

• Promethazine can cause significant sedation, agitation, hallucinations, seizures, and dystonic reactions in children 4
• The drug has been associated with possible apparent life-threatening events 4

Appropriate Use Considerations

• Antiemetics should not be used in vomiting of unknown etiology in children and adolescents 1
• The diagnosis should be established before administering promethazine 1

Preferred Alternative Agents

Given the significant safety concerns with promethazine in pediatric patients, ondansetron is generally preferred for pediatric nausea and vomiting:

• Ondansetron dosing is 0.15 mg/kg (maximum 16 mg) per dose 5
• It has a more favorable safety profile in children, though QT prolongation monitoring is still warranted 5

Bottom line: If promethazine must be used in a child over 2 years old, calculate 0.5 mg per pound (1.1 mg/kg) with typical doses of 12.5-25 mg every 4-6 hours, but strongly consider ondansetron as a safer first-line alternative. 1, 5