Septran (Trimethoprim-Sulfamethoxazole) Dosing in Children
For treatment of urinary tract infections, acute otitis media, and shigellosis in children, the recommended dose is 40 mg/kg/day of sulfamethoxazole and 8 mg/kg/day of trimethoprim, divided into two doses every 12 hours. 1, 2
Treatment Dosing by Indication
Standard Treatment Dosing (UTI, Acute Otitis Media, Shigellosis)
The FDA-approved dosing is weight-based and administered every 12 hours: 1, 2
- Children weighing 20 kg (44 lb): 1 single-strength tablet (400/80 mg) every 12 hours
- Children weighing 30 kg (66 lb): 1½ single-strength tablets or ¾ double-strength tablet every 12 hours
- Children weighing 40 kg (88 lb): 2 single-strength tablets or 1 double-strength tablet every 12 hours
Duration: 10-14 days for UTI and acute otitis media; 5 days for shigellosis 1, 2
Pneumocystis Jirovecii Pneumonia (PCP) Treatment
For documented PCP, use 75-100 mg/kg/day of sulfamethoxazole and 15-20 mg/kg/day of trimethoprim, divided into four doses every 6 hours for 14-21 days. 1, 2
The upper limit dosing guide: 1, 2
- 16 kg (35 lb): 1 tablet every 6 hours
- 24 kg (53 lb): 1½ tablets every 6 hours
- 32 kg (70 lb): 2 single-strength or 1 double-strength tablet every 6 hours
- 40 kg (88 lb): 2½ single-strength tablets every 6 hours
Bacterial Meningitis
For CNS infections including meningitis, use 10-20 mg/kg/day of trimethoprim component divided every 6-12 hours. 3
MRSA Infections
For serious MRSA infections (osteomyelitis, septic arthritis, brain abscess), use 4 mg/kg/dose of trimethoprim component every 8-12 hours, typically combined with rifampin. 3
Prophylaxis Dosing
PCP Prophylaxis
The CDC-recommended prophylactic dose is 150 mg/m²/day of trimethoprim with 750 mg/m²/day of sulfamethoxazole, divided into two doses, given on 3 consecutive days per week. 4, 5, 1, 2
Alternative dosing by body surface area: 1, 2
- 0.26-0.53 m²: ½ tablet every 12 hours (on prophylaxis days)
- 1.06 m²: 1 tablet every 12 hours (on prophylaxis days)
Maximum daily dose: Do not exceed 1,600 mg sulfamethoxazole and 320 mg trimethoprim 1, 2
UTI Prophylaxis
For long-term prophylaxis of recurrent UTI, use 2 mg/kg/day of trimethoprim with 10 mg/kg/day of sulfamethoxazole as a single daily dose. 6 Research supports intermittent dosing (every other day at bedtime) as equally effective, particularly in children with vesicoureteral reflux. 7
Age Restrictions and Special Populations
Septran is contraindicated in infants less than 2 months of age. 1, 2
Renal Impairment Adjustments
Dose adjustments are mandatory in renal dysfunction: 3, 1, 2
- CrCl >30 mL/min: Standard dosing
- CrCl 15-30 mL/min: 50% of usual dose
- CrCl <15 mL/min: Not recommended
For severe renal failure on treatment doses, increase the dosing interval (in hours) to 12 times the serum creatinine level in mg/dL, with a maximum interval of 48 hours. 8
Formulation Selection
Use liquid formulation for children weighing less than 40 kg and younger children to ensure accurate dosing. 4 The liquid suspension allows precise weight-based dosing, which is superior to tablet splitting in this population.
Monitoring Requirements
Obtain a complete blood count with differential and platelet count at initiation of therapy. 4, 5 For children on prophylactic therapy, repeat CBC monthly to detect hematologic toxicity, particularly neutropenia and thrombocytopenia. 4, 5
Monitor serum trimethoprim levels in patients with severe renal failure, targeting peak levels of 5-10 mcg/mL. 8
Common Pitfalls and Caveats
Do not use test doses when initiating Septran in children—this practice is not evidence-based and delays appropriate therapy. 4
Concomitant use with methotrexate is not contraindicated, contrary to widespread belief. 4 NSAIDs and salicylates can be given concurrently in children with normal renal function. 4
Thrombocytopenia is associated with higher serum trimethoprim levels and longer treatment duration. 8 This is the most clinically significant adverse effect requiring monitoring.
Transient neutropenia may occur but often resolves spontaneously without drug discontinuation. 7 However, if neutrophil count drops below 1,000/μL, consider temporary cessation.
Lower-than-recommended prophylactic doses (as low as two-thirds of CDC recommendations) have proven effective in preventing PCP in HIV-infected children, though this is not yet standard practice. 9 The currently recommended 150 mg/m²/day dose may exceed what is minimally necessary for prophylaxis.