What is the recommended dose of Bactrim (Sulfamethoxazole and Trimethoprim) for a 23-month-old child weighing 11.8 kg?

Bactrim Dosing for a 23-Month-Old Child Weighing 11.8 kg

For a 23-month-old child weighing 11.8 kg, the recommended dose of Bactrim (trimethoprim-sulfamethoxazole) is 40 mg/kg/day of sulfamethoxazole and 8 mg/kg/day of trimethoprim, divided into two doses given every 12 hours. 1

Calculating the Exact Dose

Based on the child's weight of 11.8 kg:

• Sulfamethoxazole: 40 mg/kg/day × 11.8 kg = 472 mg/day
• Trimethoprim: 8 mg/kg/day × 11.8 kg = 94.4 mg/day

Divided into two doses:

• Sulfamethoxazole: 236 mg per dose, twice daily
• Trimethoprim: 47.2 mg per dose, twice daily

Administration Guidelines

• Duration of therapy depends on the indication:

  • Urinary tract infection: 10-14 days 1
  • Acute otitis media: 10 days 1
  • Shigellosis: 5 days 1

• Bactrim is contraindicated in infants younger than 2 months of age 1, but this child is 23 months old and can safely receive the medication.

Formulation Options

Bactrim is available as:

1. Oral suspension (typically 40 mg trimethoprim and 200 mg sulfamethoxazole per 5 mL)
2. Tablets (single strength: 80 mg trimethoprim/400 mg sulfamethoxazole; double strength: 160 mg trimethoprim/800 mg sulfamethoxazole)

For this child, the oral suspension would be most appropriate, with approximately 5.9 mL per dose twice daily.

Important Considerations

• Monitor for adverse reactions, particularly:

  • Skin reactions (most common adverse effect) 2
  • Gastrointestinal intolerance 2
  • Hematologic reactions (rare but can include anemia, thrombocytopenia) 2

• Ensure adequate hydration during treatment to prevent crystalluria

• If preparing a suspension from tablets (not recommended if commercial suspension is available), be aware that suspensions made from tablets may produce inconsistent dosing due to foaming 3

Follow-up and Monitoring

• Clinical improvement should be seen within 48-72 hours of appropriate therapy 4
• If treating a UTI, consider follow-up urine culture after completion of therapy to ensure eradication of infection
• If no improvement is seen within 48-72 hours, reassess diagnosis and consider alternative antibiotics

This dosing recommendation follows the FDA-approved guidelines for pediatric patients and provides appropriate coverage for common pediatric infections while minimizing the risk of adverse effects.