What is the recommended dose of Sulfatrim (trimethoprim/sulfamethoxazole) for pediatric patients?

Sulfatrim Pediatric Dosing

Standard Dosing for Common Infections

For most pediatric infections in children over 2 months of age, the recommended dose is 8-12 mg/kg/day of trimethoprim (40-60 mg/kg/day of sulfamethoxazole) divided into 2 doses every 12 hours. 1, 2, 3

Dosing by Indication

Urinary Tract Infections and Acute Otitis Media:

• 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided every 12 hours for 10 days 2, 3
• This represents the standard FDA-approved dosing regimen 2, 3

Skin and Soft Tissue Infections (including MRSA):

• 8-12 mg/kg/day of trimethoprim component divided into 2 doses for 7-10 days 1, 4
• The Infectious Diseases Society of America supports this dosing range for MRSA skin infections 4
• For children approaching adult size, use 1-2 double-strength tablets twice daily 4

Shigellosis:

• 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided every 12 hours for 5 days 2, 3
• This shorter 5-day course is specifically indicated for shigellosis 2, 3

Pneumocystis jiroveci Pneumonia (PCP) Treatment:

• 15-20 mg/kg/day of trimethoprim (75-100 mg/kg/day of sulfamethoxazole) divided into 3-4 doses for 21 days 5
• This higher dosing is critical for severe PCP and should be administered intravenously initially, then transitioned to oral once acute pneumonitis resolves 5
• The FDA label supports dosing every 6 hours for PCP treatment 2, 3

PCP Prophylaxis:

• 150 mg/m²/day trimethoprim with 750 mg/m²/day sulfamethoxazole divided twice daily, given 3 consecutive days per week 2, 3
• Total daily dose should not exceed 1600 mg sulfamethoxazole and 320 mg trimethoprim 2, 3
• Alternative: 8 mg/kg/day of trimethoprim divided into two doses for prophylaxis 6

Weight-Based Dosing Table (Standard Infections)

For children 2 months or older receiving standard dosing every 12 hours 2, 3:

• 10-20 kg (22-44 lbs): 1 single-strength tablet (400 mg SMX/80 mg TMP)
• 20-30 kg (44-66 lbs): 1.5 single-strength tablets
• 30-40 kg (66-88 lbs): 2 single-strength tablets OR 1 double-strength tablet (800 mg SMX/160 mg TMP)

Critical Age Restriction

Sulfatrim is absolutely contraindicated in infants under 2 months of age due to the risk of kernicterus. 1, 2, 3

Monitoring Requirements

Obtain a complete blood count with differential and platelet count at treatment initiation and monthly during prolonged therapy. 1, 4, 6

• This monitoring is essential to detect hematologic toxicity including neutropenia, thrombocytopenia, and anemia 1, 4
• Approximately 15% of HIV-infected children experience adverse reactions, which is lower than the rate in adults 5, 1

Common Adverse Effects and Management

Dermatologic reactions (rash, including erythema multiforme and rarely Stevens-Johnson syndrome) are the most common adverse effects 5, 1:

• For mild to moderate rash: temporarily discontinue and restart when resolved 5, 4
• For urticarial rash or Stevens-Johnson syndrome: permanently discontinue 5, 1

Hematologic abnormalities include neutropenia, thrombocytopenia, and anemia 5, 1

Other effects include gastrointestinal complaints, hepatitis, and interstitial nephritis 5, 1

Renal Dosing Adjustments

For patients with impaired renal function 2, 3:

• Creatinine clearance >30 mL/min: Use standard dosing
• Creatinine clearance 15-30 mL/min: Use 50% of standard dose
• Creatinine clearance <15 mL/min: Not recommended

Common Pitfalls to Avoid

Underdosing is the most frequent error in pediatric patients. 4

• Always calculate doses based on current weight, not historical weight 4
• Failure to adjust dosing as children grow leads to subtherapeutic levels 4
• For resistant pathogens with MIC of 1 mg/liter, higher doses (12-15 mg/kg/day of trimethoprim) may be required in younger children 7, 8

Drug interactions require careful attention: 1, 4

• Use caution with methotrexate (increased toxicity risk) 1
• Monitor patients on anticoagulants, hypoglycemics, thiazide diuretics, and anticonvulsants 1

Special populations requiring caution: 1

• Patients with G6PD deficiency (risk of hemolytic anemia)
• Hepatic insufficiency
• Known sulfonamide hypersensitivity