Rectal Acetaminophen Dosing for 3-Month-Old Infant (4.5 kg)
Direct Recommendation
The recommended rectal dose of acetaminophen for a 3-month-old infant weighing 4.5 kg is approximately 67.5 mg per dose (15 mg/kg), administered every 6 hours, with a maximum daily dose not exceeding 270 mg/day (60 mg/kg/day). 1
Weight-Based Calculation
- Standard rectal dosing: 15 mg/kg per dose 1
- For this 4.5 kg infant: 15 mg/kg × 4.5 kg = 67.5 mg per dose
- Dosing interval: Every 6 hours (q6h) 1
- Maximum daily dose: 60 mg/kg/day = 270 mg/day for this infant 1
Practical Administration Considerations
- Available suppository strengths typically include 80 mg, 120 mg, and higher doses—none perfectly match the calculated 67.5 mg dose
- Clinical approach: Use the closest available strength without exceeding the calculated dose, or consider cutting an 80 mg suppository if feasible and appropriate for your clinical setting
- Alternative consideration: If precise dosing is critical and rectal administration proves impractical, oral acetaminophen suspension (160 mg/5 mL concentration) allows for more accurate weight-based dosing 1
Critical Safety Points
- Never exceed 60 mg/kg/day total when combining different acetaminophen formulations (rectal, oral, or IV) 1
- Hepatotoxicity risk: While therapeutic doses are safe, acetaminophen overdose can cause serious liver injury, though this is unlikely at recommended therapeutic levels (5-20 mcg/mL plasma concentration versus toxic levels >150 mcg/mL) 2
- Monitor cumulative exposure: Ensure caregivers understand total daily limits and avoid concurrent use of combination products containing acetaminophen 3
Clinical Monitoring
- Assess response within the first few doses for adequate fever or pain control 1
- Duration of use: Acetaminophen should be used at the lowest effective dose for the shortest necessary duration 4
- Transition when possible: Switch to oral administration as soon as clinically feasible, as it allows more precise dosing for small infants 1
Common Pitfalls to Avoid
- Do not round up to convenient suppository sizes that would exceed 15 mg/kg per dose 1
- Avoid dosing more frequently than every 6 hours, as this increases risk of exceeding daily maximum 1
- Do not assume all acetaminophen products are the same concentration—always verify the formulation strength before administration 3