Tylenol Dosing for a 9-Month-Old Weighing 18 Pounds
For a 9-month-old infant weighing 18 pounds (8.2 kg), give 82-123 mg of acetaminophen (Tylenol) every 4-6 hours as needed, not exceeding 5 doses in 24 hours. 1
Weight-Based Calculation
- The standard acetaminophen dose is 10-15 mg/kg per dose 1, 2
- For an 18-pound infant (8.2 kg):
- Minimum dose: 10 mg/kg × 8.2 kg = 82 mg
- Maximum dose: 15 mg/kg × 8.2 kg = 123 mg
- Administer every 4-6 hours as needed 1
- Maximum daily dose: 60 mg/kg/day (492 mg/day for this infant) or 5 doses in 24 hours, whichever is less 1
Practical Dosing with Available Formulations
- Oral suspension (160 mg/5 mL concentration): Give 2.5-4 mL per dose 1
- The oral syrup formulation is absorbed more rapidly and provides more consistent response compared to suppositories 1
- Dosing can be rounded by up to 15% for ease of home administration 3
Critical Safety Considerations
- Never exceed 60 mg/kg per day or 5 doses in 24 hours to prevent hepatotoxicity 1
- For infants under 3 months, acetaminophen is the only recommended analgesic, but this 9-month-old is beyond that restriction 1
- Studies show that 27-62% of parents inadvertently underdose or overdose acetaminophen, with infants under 1 year at highest risk for dosing errors 4, 5
- Parents who base dosing on weight (rather than age alone) are significantly less likely to misdose medication 5
Clinical Context
- Acetaminophen will improve comfort but does not prevent febrile seizures 1
- For post-vaccination fever, acetaminophen can be given at the time of vaccination and every 4 hours for 24 hours 1
- If alternating with ibuprofen becomes necessary (though ibuprofen is generally not recommended under 6 months), stagger medications every 3-4 hours 1