What is the recommended dose of Septra (trimethoprim/sulfamethoxazole) for a pediatric patient weighing 17 kilograms with normal renal function?

Septra Dosing for a 17 kg Pediatric Patient

For a 17 kg child with normal renal function, administer Septra at 8 mg/kg/day of the trimethoprim component (68 mg trimethoprim/340 mg sulfamethoxazole per day) divided into two doses every 12 hours for treatment of common infections like urinary tract infections or acute otitis media. 1

Treatment Dosing by Weight

For standard infections (UTI, acute otitis media, shigellosis):

• A 17 kg child falls between the 10 kg and 20 kg weight categories in FDA dosing tables 1
• The FDA-approved dosing is 40 mg/kg/day sulfamethoxazole and 8 mg/kg/day trimethoprim, divided every 12 hours 1
• For this 17 kg patient, this equals approximately 136 mg trimethoprim and 680 mg sulfamethoxazole per day, or 68 mg/170 mg per dose 1

Practical Tablet Dosing

• The closest practical dose using standard tablets would be 1 single-strength tablet (80 mg trimethoprim/400 mg sulfamethoxazole) every 12 hours, which slightly exceeds the calculated dose but remains within safe parameters 1
• Alternatively, liquid formulation allows more precise dosing and is recommended for children under 20 kg 2

Indication-Specific Dosing Variations

For Pneumocystis Jiroveci Pneumonia (Treatment)

• Use 15-20 mg/kg/day trimethoprim (75-100 mg/kg/day sulfamethoxazole) divided every 6 hours for 14-21 days 3, 1
• For this 17 kg child: 255-340 mg trimethoprim per day (51-68 mg every 6 hours) 3

For PCP Prophylaxis

• Use 150 mg/m²/day trimethoprim with 750 mg/m²/day sulfamethoxazole divided into two doses, given 3 consecutive days per week 4, 2
• This is the CDC-recommended regimen for immunocompromised children 4

For MRSA Infections

• Use 4 mg/kg/dose of trimethoprim component every 8-12 hours, typically combined with rifampin 3, 5
• For this 17 kg child: 68 mg trimethoprim per dose every 8-12 hours 5

Critical Dosing Considerations

Renal Function Adjustments

• With creatinine clearance >30 mL/min: use standard dosing 5, 1
• With creatinine clearance 15-30 mL/min: reduce to 50% of usual dose 5, 1
• With creatinine clearance <15 mL/min: Septra is not recommended 5, 1

Monitoring Requirements

• Obtain complete blood count with differential and platelet count at initiation 2, 5
• For prophylactic therapy, repeat CBC monthly to detect hematologic toxicity 2, 5
• Approximately 15% of children experience substantial adverse reactions including rash, gastrointestinal disturbances, and hematologic abnormalities 3, 4

Common Pitfalls to Avoid

• Do not use Septra in children under 2 months of age—it is contraindicated 1
• Liquid formulation provides more accurate dosing than tablets for children weighing less than 20 kg 2
• Recent pharmacokinetic data suggests that 8 mg/kg/day trimethoprim divided every 12 hours achieves appropriate exposure matching adult dosing and targets bacteria with MIC ≤0.5 mg/L in >90% of children 6
• Test doses are not recommended when initiating Septra therapy 2