Promethazine Suppository Dosing for a 5-Year-Old (14.06 kg)
Give 12.5 mg promethazine suppository every 4-6 hours as needed, not to exceed 25 mg per day for this child.
Weight-Based Dosing Calculation
For nausea and vomiting in children, the FDA-approved dosing is 0.5 mg per pound of body weight 1.
- 14.06 kg = 31 pounds
- Calculation: 31 lbs × 0.5 mg/lb = 15.5 mg per dose
However, since promethazine suppositories are commercially available in 12.5 mg and 25 mg strengths, and given this child's weight, 12.5 mg is the appropriate starting dose 1.
Dosing Frequency and Maximum Daily Dose
- Frequency: Every 4-6 hours as necessary 2, 1
- Maximum consideration: While the FDA label states doses may be repeated at 4-6 hour intervals 1, for a child of this size and age, limit to 2 doses (25 mg total) in 24 hours to minimize risk of CNS depression and other adverse effects
Critical Safety Considerations
Age Restriction
Promethazine is contraindicated in children under 2 years of age due to risk of fatal respiratory depression 1. At 5 years old, this child meets the minimum age requirement.
Dose Adjustment Principle
The FDA label explicitly states: "After initiation of treatment, in children or adults, dosage should be adjusted to the smallest amount adequate to relieve symptoms" 1. Start with 12.5 mg and assess response before considering higher doses.
Serious Adverse Effects to Monitor
- Respiratory depression - particularly concerning when combined with other CNS depressants 2, 3
- CNS depression and oversedation 2
- Extrapyramidal symptoms 2, 3
- Anticholinergic effects 2
Alternative Considerations
Given the safety concerns with promethazine, particularly in pediatric populations, consider ondansetron 4 mg (0.15 mg/kg) every 6-8 hours as a safer first-line alternative 2. Ondansetron has a superior safety profile with the primary concern being QTc prolongation rather than respiratory depression.
When Promethazine May Be Preferred
- Ondansetron unavailable or contraindicated
- Need for sedative effect in addition to antiemetic action
- Previous good response to promethazine without adverse effects