Bactrim Dosing for a 30 kg Pediatric Patient
For a 30 kg child with normal renal function, administer Bactrim 240 mg trimethoprim/1200 mg sulfamethoxazole (8 mg/kg trimethoprim component) divided into two doses every 12 hours for most infections. 1, 2
Standard Dosing Calculation
The FDA-approved pediatric dosing for Bactrim is 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per 24 hours, divided every 12 hours for urinary tract infections, acute otitis media, and shigellosis. 1, 2
For a 30 kg patient:
- Trimethoprim: 240 mg/day (120 mg every 12 hours)
- Sulfamethoxazole: 1200 mg/day (600 mg every 12 hours)
- This equals 1.5 single-strength tablets (400mg/80mg) every 12 hours 1, 2
Indication-Specific Adjustments
Mild-to-Moderate Infections
For uncomplicated infections (UTI, skin/soft tissue), use the standard 8-10 mg/kg/day trimethoprim component divided every 12 hours. 3
Severe Infections
For serious infections like severe MRSA, increase to 10-12 mg/kg/day trimethoprim component, or up to 15-20 mg/kg/day divided every 6-8 hours for life-threatening infections. 3 This would translate to 300-360 mg/day trimethoprim for moderate severe infections, or up to 450-600 mg/day for life-threatening cases in this 30 kg patient.
Pneumocystis Pneumonia
For documented PCP, use 75-100 mg/kg sulfamethoxazole and 15-20 mg/kg trimethoprim per 24 hours, divided every 6 hours for 14-21 days. 1, 2 For this 30 kg patient, this equals 450-600 mg trimethoprim/day (112.5-150 mg every 6 hours).
Practical Formulation Guidance
Use liquid formulation for accurate dosing in children <40 kg, particularly when doses don't align perfectly with tablet strengths. 3 The 30 kg patient falls into the range where 1.5 single-strength tablets every 12 hours is appropriate, but liquid may provide more precise dosing. 1, 2
Critical Safety Monitoring
- Obtain baseline CBC with differential and platelets before initiating therapy 3
- Repeat CBC monthly during prolonged therapy to monitor for hematologic toxicity 3
- Use with extreme caution in G6PD deficiency due to hemolytic anemia risk 3
- Monitor for drug interactions with warfarin, methotrexate, and oral hypoglycemics 3
Important Contraindications
Bactrim is contraindicated in children <2 months of age. 1, 2 This 30 kg patient is well beyond this age restriction.
Renal Adjustment
With normal renal function, no dose adjustment is needed. However, if creatinine clearance is 15-30 mL/min, reduce dose by 50%; if <15 mL/min, Bactrim is not recommended. 1, 2