What is the appropriate prescription for Bactrim (trimethoprim/sulfamethoxazole) for a 2-year-old with a skin infection?

Bactrim Prescription for Skin Infection in a 2-Year-Old

For a 2-year-old with a skin infection, prescribe Bactrim (trimethoprim-sulfamethoxazole) at 8-12 mg/kg/day based on the trimethoprim component, divided into 2 oral doses, for 5-10 days depending on clinical response. 1

Dosing Specifics

The standard pediatric dose is 8-12 mg/kg/day (based on trimethoprim component) given orally in 2 divided doses. 1 For practical prescribing:

• A 2-year-old typically weighs 12-14 kg
• This translates to approximately 96-168 mg of trimethoprim per day (480-840 mg sulfamethoxazole)
• Divide into twice-daily dosing (every 12 hours)
• Bactrim suspension contains 40 mg trimethoprim/200 mg sulfamethoxazole per 5 mL 1

Treatment Duration

Treat for 5-10 days based on clinical response, with most uncomplicated skin infections requiring 7 days. 2 For MRSA skin abscesses specifically, a 10-day course is superior to 3 days in reducing treatment failure and recurrence. 3

When to Use Bactrim

Bactrim is appropriate for:

• Purulent skin infections (abscesses, furuncles) where community-acquired MRSA is suspected 2
• Empirical coverage when the child has not responded to beta-lactam therapy 2
• Confirmed MRSA infections based on culture results 2

Critical Limitations in Young Children

If streptococcal coverage is needed (non-purulent cellulitis), Bactrim MUST be combined with a beta-lactam such as amoxicillin, as it has poor activity against beta-hemolytic streptococci. 2 This is a common pitfall—using Bactrim alone for cellulitis without purulent drainage risks treatment failure.

For minor superficial infections like impetigo, consider mupirocin 2% topical ointment instead, which avoids systemic antibiotic exposure. 2

Important Safety Considerations

• Bactrim is contraindicated in infants under 2 months of age 1
• At 2 years old, this child is just above the minimum age threshold
• Monitor for sulfa allergy reactions 1
• Ensure adequate hydration to prevent crystalluria
• Avoid in patients with sulfa allergies—consider clindamycin as an alternative 1

Clinical Decision Algorithm

1. Determine infection type:

   • Purulent (abscess, pustules) → Bactrim alone is appropriate 2
   • Non-purulent (cellulitis without drainage) → Add amoxicillin for streptococcal coverage 2

2. Assess severity:

   • Mild-moderate, outpatient → Oral Bactrim as above 2
   • Severe, systemic toxicity, hospitalized → IV vancomycin or clindamycin instead 2

3. Consider incision and drainage:

   • For abscesses, surgical drainage is the primary treatment; antibiotics are adjunctive 2
   • Antibiotics reduce new lesion formation and recurrence in MRSA cases 2, 3

Alternative Agents

If Bactrim is not suitable:

• Clindamycin 10-13 mg/kg/dose every 6-8 hours (if local resistance <10%) 2
• Linezolid 10 mg/kg/dose every 8 hours for children under 12 years 2
• Tetracyclines are contraindicated in children under 8 years of age 2