Acetaminophen Dosing for a 22-lb Infant
For a 22-lb (10 kg) infant, give 100–150 mg of acetaminophen per dose, administered every 4–6 hours as needed, not exceeding 5 doses in 24 hours.
Weight-Based Calculation
- A 22-lb infant weighs exactly 10 kg 1
- The standard acetaminophen dose is 10–15 mg/kg per dose 1, 2, 3
- For a 10 kg child, this calculates to:
- Minimum dose: 100 mg (10 mg/kg × 10 kg)
- Maximum dose: 150 mg (15 mg/kg × 10 kg)
Dosing Frequency and Maximum Daily Limits
- Administer doses every 4–6 hours as needed for fever or pain 1, 2
- Never exceed 60 mg/kg per day (600 mg/day for a 10 kg infant) 1
- Never give more than 5 doses in 24 hours 1
Optimal Dosing Strategy
- The 15 mg/kg dose (150 mg) is preferred over 10 mg/kg for this weight because pharmacokinetic modeling demonstrates that 10 mg/kg fails to reach therapeutic plasma concentrations (10–20 μg/mL) needed for effective antipyresis 4
- The 15 mg/kg dose provides more consistent fever reduction and maintains temperature control for approximately 6 hours 5
- A 10 mg/kg dose produces peak plasma concentrations of only 6.38–8.55 μg/mL, below the therapeutic threshold, while 15 mg/kg achieves 9.57–12.8 μg/mL 4
Practical Administration
- Use oral liquid formulation (syrup/suspension) rather than suppositories, as oral formulations are absorbed more rapidly and provide more consistent responses 1, 5
- Common infant acetaminophen concentrations are 160 mg/5 mL, so for a 10 kg infant:
- 100 mg dose = 3.1 mL
- 150 mg dose = 4.7 mL
Special Circumstances Requiring Dose Reduction
Reduce to 10 mg/kg (100 mg) per dose if the infant has:
- Chronic malnutrition or has fasted for more than 8 hours without adequate caloric intake 1
- Known liver disease 1
- Concurrent use of medications that induce cytochrome P450 enzymes (such as isoniazid) 1
Critical Safety Considerations
- Age verification is essential: Acetaminophen is the only recommended analgesic for infants under 3 months, and dosing must be weight-based 1
- For infants under 6 months, ibuprofen is not recommended as an alternative 1
- Parents frequently underdose acetaminophen when using age-based rather than weight-based dosing, leading to inadequate fever control 4
- Always use weight-based dosing rather than age-based recommendations to ensure therapeutic efficacy 4, 3