Bactrim Dosing for a 2-Year-Old Child
For a 2-year-old child, the appropriate dose of Bactrim (trimethoprim-sulfamethoxazole) suspension is based on 8 mg/kg/day of the trimethoprim component divided into two doses every 12 hours, which translates to approximately 5 mL of the 200-40 mg/5 mL suspension twice daily for an average-sized 2-year-old (approximately 12 kg). 1, 2
Weight-Based Dosing Calculation
- The standard pediatric dosing is 8 mg/kg/day of trimethoprim given in two divided doses (or 40 mg/kg/day of sulfamethoxazole), administered every 12 hours 2
- For a typical 2-year-old weighing approximately 12 kg, this equals 96 mg trimethoprim per day (48 mg per dose) 2
- Using Bactrim suspension 200-40 mg/5 mL (which contains 40 mg trimethoprim per 5 mL), this translates to 6 mL twice daily for a 12 kg child 2
- The CDC recommends the simplified approach of 5 mg/kg (trimethoprim component) every 12 hours PO for children ≥2 months to ≤17 years, which would be approximately 60 mg trimethoprim per dose (7.5 mL) for a 12 kg child 1
Age Restrictions and Safety
- Bactrim is contraindicated in infants younger than 2 months of age 2
- For children 2 months and older, Bactrim is FDA-approved for urinary tract infections, acute otitis media, and shigellosis 2
Practical Dosing Table for Common Indications
For urinary tract infections and acute otitis media in a 2-year-old (typically 10-13 kg):
- Weight 10 kg (22 lbs): 1 tablet (400 mg/80 mg) or 5 mL suspension every 12 hours 2
- This provides the target dose of 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours 2
Duration of Therapy
Important Prescribing Considerations
- Always prescribe 10-30% extra volume beyond the calculated amount to account for spillage and measurement errors, as studies show pharmacies frequently dispense inadequate volumes 3
- Request a medication-measuring device on the prescription, as one-third of pharmacies fail to provide one 3
- For a 10-day course at 5 mL twice daily, prescribe at least 110-120 mL (100 mL needed plus 10-20% extra) 3
Monitoring and Precautions
- Contraindicated in patients with known hypersensitivity to trimethoprim or sulfonamides 1
- Monitor for gastrointestinal effects (nausea, vomiting, diarrhea) and hypersensitivity reactions (rashes, drug fever) 1
- For prolonged therapy, consider periodic complete blood counts to monitor for hematologic adverse effects 1
- Rare but serious reactions include Stevens-Johnson syndrome, toxic epidermal necrolysis, and blood dyscrasias 1