What is the dosing for cotrimoxazole (trimethoprim/sulfamethoxazole) in pediatric patients with skin infections?

Cotrimoxazole Dosing for Pediatric Skin Infections

For pediatric skin infections, trimethoprim-sulfamethoxazole (TMP-SMX) should be dosed at 8-12 mg/kg/day (based on the trimethoprim component) divided into 2 doses orally for skin and soft tissue infections. 1

Dosing Guidelines

• For skin and soft tissue infections (SSTI), including those caused by methicillin-resistant Staphylococcus aureus (MRSA), the recommended dose is 8-12 mg/kg/day based on the trimethoprim component, given in 2 divided doses orally 1
• For standard formulations, this typically translates to:
  • For children weighing <40 kg: 8-12 mg/kg/day of trimethoprim component in 2 divided doses 1
  • For children approaching adult size: 1-2 double-strength tablets twice daily (each double-strength tablet contains 160 mg trimethoprim and 800 mg sulfamethoxazole) 1
• Duration of therapy for uncomplicated skin infections is typically 7 days, depending on clinical response 1

Clinical Considerations

• For MRSA skin infections specifically, a 10-day course is more effective than a 3-day course in preventing treatment failure and recurrence 2
• TMP-SMX is considered bactericidal against many skin pathogens, though clinical efficacy data for skin infections is somewhat limited compared to other indications 1
• When treating skin abscesses, surgical drainage remains the primary intervention, with TMP-SMX as adjunctive therapy 2
• Doses should be adjusted upward as the child grows to maintain appropriate therapeutic levels 1

Special Populations and Considerations

• TMP-SMX is not recommended for neonates; refer to specific neonatal dosing guidelines if treatment is absolutely necessary 1
• For children with HIV infection receiving TMP-SMX for Pneumocystis jiroveci pneumonia prophylaxis, higher doses are used: 150/750 mg/m² per day of TMP-SMX divided in 2 doses three times weekly 1
• Concomitant use of TMP-SMX with methotrexate is not contraindicated, though monitoring may be warranted 1

Monitoring and Safety

• Complete blood counts with differential and platelet count should be performed at initiation of TMP-SMX therapy and at monthly intervals during prolonged treatment to assess for hematologic toxicity 1
• Monitor for adverse reactions, which may include:
  • Rash (including erythema multiforme and rarely Stevens-Johnson syndrome)
  • Hematologic abnormalities (neutropenia, thrombocytopenia)
  • Gastrointestinal complaints
  • Hepatotoxicity (rare but reported in pediatric patients) 3
• If mild to moderate skin rash occurs, TMP-SMX can be temporarily discontinued and restarted when the rash resolves 1
• If life-threatening reactions occur (anaphylaxis, Stevens-Johnson syndrome), the drug should be permanently discontinued 1

Common Pitfalls

• Underdosing is a common error in pediatric patients; ensure doses are calculated correctly based on weight or body surface area 1
• Failure to adjust dosing as children grow can lead to subtherapeutic levels 1
• Not completing the full course of therapy may lead to treatment failure and recurrence, particularly with MRSA infections 2
• Overlooking potential drug interactions, especially in patients on multiple medications 1

By following these evidence-based dosing guidelines, clinicians can effectively treat pediatric skin infections while minimizing the risk of adverse events and antimicrobial resistance.