Co-trimoxazole Pediatric Syrup Dosage and Uses
For most pediatric infections, administer co-trimoxazole at 8 mg/kg/day trimethoprim (40 mg/kg/day sulfamethoxazole) divided into 2 doses every 12 hours, which is the standard recommended regimen supported by both FDA labeling and major pediatric guidelines. 1, 2
Standard Dosing by Weight
The FDA-approved dosing for children over 2 months is 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided every 12 hours. 2 This translates to practical weight-based dosing:
- 10 kg (22 lbs): 1 single-strength tablet equivalent (80 mg TMP/400 mg SMX) every 12 hours 1
- 20 kg (44 lbs): 1 single-strength tablet every 12 hours 2
- 30 kg (66 lbs): 1½ single-strength tablets every 12 hours 2
- 40 kg (88 lbs): 2 single-strength tablets (or 1 double-strength) every 12 hours 2
For children under 20 kg, liquid formulation is strongly recommended for accurate dosing. 1, 3
Indication-Specific Dosing
Urinary Tract Infections and Acute Otitis Media
Administer 8 mg/kg trimethoprim (40 mg/kg sulfamethoxazole) every 12 hours for 10 days. 2 This is the FDA-approved standard regimen. 2
Non-Severe Pneumonia
The recommended dose is 8 mg/kg trimethoprim per dose twice daily for 5 days. 1 However, amoxicillin is now preferred over co-trimoxazole as first-line therapy for non-severe pneumonia due to concerns about resistance and lack of anti-malarial activity. 4 Co-trimoxazole should be reserved as second-line therapy when amoxicillin fails. 4
Severe MRSA Infections
For serious MRSA infections including osteomyelitis, use 4 mg/kg trimethoprim every 8-12 hours (higher end of dosing range), typically combined with rifampin for >6 weeks. 4, 1 For life-threatening infections, doses up to 15-20 mg/kg/day trimethoprim divided every 6-8 hours may be used. 1
Pneumocystis Jiroveci Pneumonia (PCP)
Treatment requires 15-20 mg/kg/day trimethoprim (75-100 mg/kg/day sulfamethoxazole) divided every 6 hours for 14-21 days. 3, 2 This is substantially higher than standard dosing and requires close monitoring. 3
For PCP prophylaxis, use 150 mg/m²/day trimethoprim with 750 mg/m²/day sulfamethoxazole divided twice daily, given 3 consecutive days per week, with a maximum of 320 mg trimethoprim/1600 mg sulfamethoxazole daily. 1, 3
Shigellosis
Use the same dose as UTI (8 mg/kg trimethoprim every 12 hours) but for only 5 days. 2
Critical Safety Considerations
Age Restrictions
Co-trimoxazole is absolutely contraindicated in infants under 2 months of age due to the risk of kernicterus. 5, 2 This is a non-negotiable contraindication. 5
Renal Impairment Adjustments
For creatinine clearance 15-30 mL/min, reduce the dose by 50%. 1, 2 Specifically:
- CrCl 10-50 mL/min: Administer 3-5 mg/kg every 12 hours (instead of every 6-8 hours) 1
- CrCl <10 mL/min: Administer 3-5 mg/kg every 24 hours 1
- CrCl <15 mL/min: Use is not recommended; consider alternative agents 1, 2
Mandatory Monitoring
Obtain a complete blood count with differential and platelet count at treatment initiation, and repeat monthly during prolonged therapy to detect hematologic toxicity including neutropenia, thrombocytopenia, and anemia. 1, 3, 5 This is essential as approximately 15% of children experience substantial adverse reactions. 3
Screen for G6PD deficiency before initiating therapy due to hemolytic anemia risk. 1 This is particularly important in at-risk populations. 5
Hydration Requirements
Ensure adequate hydration (at least 1.5 liters daily for older children, proportionally adjusted for younger children) to prevent crystalluria. 1
Common Pitfalls to Avoid
Do not use co-trimoxazole as first-line therapy for pneumonia in malaria-endemic areas because it lacks anti-malarial activity, unlike alternatives. 4 Amoxicillin is now the preferred first-line agent. 4
Do not assume standard dosing is appropriate for severe infections. MRSA osteomyelitis and PCP require substantially higher doses than routine UTI treatment. 4, 1, 3
Do not overlook drug interactions. Co-trimoxazole increases methotrexate toxicity, enhances warfarin's anticoagulant effect, and increases hypoglycemia risk with oral hypoglycemics. 1, 5
Treatment failure in pneumonia is defined as development of chest indrawing, central cyanosis, stridor while calm, or persistently raised respiratory rate at 72 hours (48 hours in high HIV prevalence areas). 4 If failure occurs on co-trimoxazole, switch to amoxicillin 50 mg/kg in two divided doses. 4
Duration of Treatment
Standard treatment duration is 5-10 days for most infections (5 days for shigellosis and pneumonia, 10 days for UTI and otitis media). 2 Severe infections like osteomyelitis require >6 weeks of therapy. 4 PCP treatment requires 14-21 days. 3, 2