What is the appropriate dose of Bactrim DS (sulfamethoxazole‑trimethoprim) suspension 200‑40 mg per 5 mL for a child weighing 14.7 kg?

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Last updated: September 15, 2026 • View editorial policy

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Bactrim DS Suspension Dosing for 14.7 kg Child

For a child weighing 14.7 kg, administer Bactrim suspension (200-40 mg/5 mL) at 15 mL (600 mg sulfamethoxazole/120 mg trimethoprim) every 12 hours for most common infections.

Dosing Calculation

The standard pediatric dosing for Bactrim is 40 mg/kg/day of sulfamethoxazole and 8 mg/kg/day of trimethoprim, divided into two doses every 12 hours 1. This is the FDA-approved dosing for urinary tract infections, acute otitis media, and shigellosis in children over 2 months of age.

For a 14.7 kg child:

  • Sulfamethoxazole: 40 mg/kg/day × 14.7 kg = 588 mg/day (294 mg per dose)
  • Trimethoprim: 8 mg/kg/day × 14.7 kg = 117.6 mg/day (58.8 mg per dose)

Since the suspension contains 200 mg sulfamethoxazole and 40 mg trimethoprim per 5 mL:

  • 15 mL every 12 hours provides 600 mg sulfamethoxazole and 120 mg trimethoprim per dose
  • This delivers approximately 41 mg/kg/day sulfamethoxazole and 8.2 mg/kg/day trimethoprim

Context-Specific Dosing

For Skin/Soft Tissue Infections (including MRSA)

The same dosing applies: 8-12 mg/kg/day of trimethoprim component in 2 divided doses 2, 3, 2. For this child, 15 mL twice daily falls within this range and is appropriate.

For Pneumocystis jirovecii Pneumonia (Treatment)

Much higher doses are required: 75-100 mg/kg/day sulfamethoxazole and 15-20 mg/kg/day trimethoprim in 4 divided doses 1. This would require 27.5-37.5 mL every 6 hours, which is substantially higher than standard dosing.

For PCP Prophylaxis

Lower doses suffice: 150 mg/m²/day sulfamethoxazole with 30 mg/m²/day trimethoprim in 2 divided doses 4. For a child of this weight, this typically translates to approximately 10 mL twice daily.

Important Caveats

  • Age restriction: Bactrim is contraindicated in children under 2 months of age due to risk of kernicterus 5, 1

  • Duration: Standard treatment courses are typically 10-14 days for UTIs, 5 days for shigellosis and traveler's diarrhea, and 7 days for skin infections depending on clinical response 1

  • Renal function: Dose reduction is required if creatinine clearance is below 30 mL/min 1

  • Resistance concerns: Recent pharmacovigilance data shows TMP-SMX use is associated with increased resistance in bacteremia isolates (RR 2.91-3.35) 6, 7, though this must be balanced against efficacy for specific indications

  • Adverse effects: Monitor for rash (2.5-fold increased risk vs other antibiotics), hyperkalemia (56-fold increase vs azithromycin), and hematologic abnormalities including pancytopenia 7

The 15 mL twice daily dosing provides adequate exposure matching adult therapeutic levels and achieves pharmacodynamic targets for organisms with MIC ≤0.5 mg/L 8. For organisms with higher MICs (up to 1 mg/L), doses of 12-15 mg/kg/day of trimethoprim component may be needed 8.

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.