What is the recommended weight-based dose of Promethazine (promethazine) for a pediatric patient?

Promethazine DM Weight-Based Dosing in Pediatrics

Critical Safety Warning

Promethazine is contraindicated in children under 2 years of age due to fatal respiratory depression risk, and weight-based dosing for nausea/vomiting is 0.5 mg per pound (approximately 1.1 mg/kg) with doses of 12.5-25 mg repeated every 4-6 hours as needed. 1

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Age Restrictions and Black Box Warning

• Promethazine is absolutely contraindicated in children under 2 years of age due to FDA black box warning regarding fatal respiratory depression 2, 1
• This contraindication applies to all formulations and indications 1
• The respiratory depression risk is particularly concerning when combined with other sedating medications 3

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Weight-Based Dosing for Children ≥2 Years

For Nausea and Vomiting

• The standard weight-based dose is 0.5 mg per pound of body weight (approximately 1.1 mg/kg) 1
• Typical dosing range: 12.5-25 mg per dose 1
• Dosing interval: Every 4-6 hours as necessary 1
• Dose should be adjusted based on age, weight, and severity of condition 1

For Motion Sickness

• 12.5-25 mg twice daily 1
• Initial dose should be given 30-60 minutes before travel 1
• Repeat dose 8-12 hours later if necessary 1

For Allergy

• 6.25-12.5 mg three times daily, or single 25 mg dose at bedtime 1
• After initiation, adjust to smallest effective dose 1

For Sedation

• 12.5-25 mg at bedtime for nighttime sedation 1
• For preoperative use: 0.5 mg per pound of body weight in combination with appropriately reduced narcotic/barbiturate doses 1

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Critical Monitoring Requirements

Respiratory Depression Risk

• Frequent monitoring is essential, particularly in the first 30 minutes after administration 3
• One case series documented respiratory arrest within 30 minutes at doses as low as 0.07 ml/kg of combination products containing promethazine 3
• Respiratory rates as low as 12-20 per minute were observed in patients developing respiratory depression 3

Drug Interactions

• Extreme caution when combining with other sedating medications (opioids, barbiturates, benzodiazepines) 3
• Combination products (meperidine-promethazine-chlorpromazine) have documented severe adverse effects including respiratory arrest 3
• Appropriately reduce doses of concomitant narcotics or barbiturates when using promethazine 1

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Route of Administration Considerations

• Oral route is preferred when tolerated 1
• Rectal suppositories are an alternative when oral medication cannot be tolerated 1
• Parenteral administration should be reserved for situations where oral/rectal routes are not feasible 1

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Key Clinical Pitfalls

• Do not use age-based dosing alone—weight-based calculation (0.5 mg/lb or ~1.1 mg/kg) is more accurate 1
• Never exceed recommended doses even in older/larger children 1
• Avoid in children with respiratory compromise or those receiving other respiratory depressants 2, 3
• Do not use for vomiting of unknown etiology in children and adolescents 1
• Long duration of action requires extended observation periods, particularly important for infants in car safety seats due to re-sedation risk 2

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Practical Dosing Algorithm

1. Verify age ≥2 years (absolute contraindication if younger) 1
2. Calculate weight in pounds × 0.5 mg = dose per administration 1
3. Round to nearest available strength: 12.5 mg or 25 mg 1
4. Administer every 4-6 hours as needed (not to exceed this frequency) 1
5. Monitor respiratory rate closely for first 30-60 minutes 3
6. Titrate to lowest effective dose after initial response 1