Septra Pediatric Dosing
Standard Dosing Recommendation
For most infections in children over 2 months of age, administer Septra at 8-12 mg/kg/day of trimethoprim (40-60 mg/kg/day of sulfamethoxazole) divided into 2 doses given every 12 hours. 1, 2, 3
Age-Based Contraindications
- Never use Septra in infants under 2 months of age due to the risk of kernicterus 1, 3
- This is an absolute contraindication regardless of indication 1
Weight-Based Dosing Table
For achieving the standard 8 mg/kg trimethoprim per dose every 12 hours 3:
| Weight | Dose per administration |
|---|---|
| 10 kg (22 lbs) | 1 single-strength tablet (80 mg TMP/400 mg SMX) |
| 20 kg (44 lbs) | 1 single-strength tablet |
| 30 kg (66 lbs) | 1½ single-strength tablets |
| 40 kg (88 lbs) | 2 single-strength tablets OR 1 double-strength tablet |
Indication-Specific Dosing
Mild-to-Moderate Infections
- Urinary tract infections, skin/soft tissue infections: 8-10 mg/kg/day trimethoprim divided every 12 hours for 7-10 days 1, 2, 3
- Acute otitis media: 8 mg/kg/day trimethoprim divided every 12 hours for 10 days 3
Severe Infections
- Serious MRSA infections: 10-12 mg/kg/day trimethoprim divided every 12 hours, or up to 15-20 mg/kg/day divided every 6-8 hours for life-threatening infections 2
- Severe MRSA osteomyelitis: 4 mg/kg/dose trimethoprim every 8-12 hours, typically combined with rifampin for >6 weeks 2
Pneumocystis Jirovecii Pneumonia
- Treatment: 15-20 mg/kg/day trimethoprim (75-100 mg/kg/day sulfamethoxazole) divided every 6 hours for 14-21 days 3
- Prophylaxis: 150 mg/m²/day trimethoprim (750 mg/m²/day sulfamethoxazole) divided twice daily, given 3 consecutive days per week, with maximum 320 mg trimethoprim/1600 mg sulfamethoxazole daily 1, 3
Other Specific Indications
- Shigellosis: 8 mg/kg/day trimethoprim divided every 12 hours for 5 days 3
- Pertussis prophylaxis: 8 mg/kg/day trimethoprim divided every 12 hours for 14 days 1
Renal Impairment Adjustments
Dose reduction is mandatory in renal insufficiency to prevent toxicity 2:
- CrCl 15-30 mL/min: Reduce dose by 50% 2
- CrCl 10-50 mL/min: Administer 3-5 mg/kg every 12 hours (instead of every 6-8 hours for treatment dosing) 2
- CrCl <10 mL/min: Administer 3-5 mg/kg every 24 hours OR use alternative agent 2
- CrCl <15 mL/min: Use not recommended 3
Formulation Considerations
- Use liquid formulation for children weighing <16 kg to ensure accurate dosing 2
- Liquid suspension allows for precise weight-based dosing in younger children 2
Monitoring Requirements
Obtain complete blood count with differential and platelet count at treatment initiation 1, 2
- Repeat monthly during prolonged therapy to assess for hematologic toxicity including neutropenia, thrombocytopenia, and anemia 1, 2
- Monitor for dermatologic reactions, gastrointestinal effects, and hepatic/renal function 1
Critical Safety Precautions
High-Risk Populations Requiring Caution
- G6PD deficiency: Screen before initiating therapy due to hemolytic anemia risk 2, 4
- Renal insufficiency: Requires dose adjustment as outlined above 1, 2
- Hepatic insufficiency: Use with extreme caution; avoid in severe hepatic impairment 1, 2
Hydration Requirements
- Ensure adequate hydration (at least 1.5 liters daily) to prevent crystalluria 2
Adverse Reactions Management
- Adverse reactions occur in approximately 15% of HIV-infected children 1
- For mild rash: Temporarily discontinue and restart when resolved 1
- For urticarial rash or Stevens-Johnson syndrome: Permanently discontinue 1
Important Drug Interactions
Exercise caution when combining with 1, 2:
- Methotrexate: May increase toxicity
- Warfarin and other anticoagulants: Enhanced anticoagulant effect
- Oral hypoglycemics: Increased hypoglycemia risk
- Thiazide diuretics and anticonvulsants: Potential interactions
Clinical Pitfalls to Avoid
- Do not use as monotherapy for non-purulent cellulitis where streptococci are likely pathogens, as Septra has poor activity against beta-hemolytic streptococci 4
- Do not use for mixed aerobic-anaerobic wound infections without additional anaerobic coverage 4
- Avoid in patients with sulfa allergies 4
- Contraindicated in third trimester of pregnancy and nursing mothers due to kernicterus risk 4
Evidence Quality Note
The standard 8-12 mg/kg/day dosing divided every 12 hours achieves therapeutic targets for bacteria with MIC ≤0.5 mg/L in >90% of children and matches adult exposure 2, 5. Higher doses (12-15 mg/kg/day) may be needed for organisms with MIC up to 1 mg/L 5.