Bactrim DS Dosage for a 13-Year-Old with Urinary Tract Infection
For a 13-year-old with a urinary tract infection, the recommended dose of Bactrim DS (trimethoprim/sulfamethoxazole) is 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per 24 hours, divided into two doses given every 12 hours for 10-14 days. 1
Dosage Calculation
The FDA-approved dosing for children with urinary tract infections is weight-based:
- 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours
- Given in two divided doses every 12 hours
- Treatment duration: 10-14 days
Weight-Based Dosing Guide
For a 13-year-old, the appropriate dose depends on the patient's weight:
| Weight | Dose (every 12 hours) |
|---|---|
| 10 kg (22 lb) | 1 regular strength tablet |
| 20 kg (44 lb) | 1 regular strength tablet |
| 30 kg (66 lb) | 1½ regular strength tablets |
| 40 kg (88 lb) | 2 regular strength tablets or 1 DS tablet |
Most 13-year-olds will weigh at least 40 kg, which would typically require 1 DS tablet every 12 hours. 1
Treatment Duration
The recommended treatment duration for urinary tract infections is 10-14 days, as specified in the FDA labeling. 1 This is consistent with clinical practice guidelines for the treatment of UTIs in pediatric patients.
Important Considerations
Contraindications
- Bactrim is contraindicated in children less than 2 months of age 1
- Should not be used in patients with known sulfa allergy
Renal Function
- For patients with impaired renal function, dose adjustment is necessary:
- Creatinine clearance >30 mL/min: Standard regimen
- Creatinine clearance 15-30 mL/min: Half the usual regimen
- Creatinine clearance <15 mL/min: Not recommended 1
Monitoring
- Monitor for adverse effects including skin rash, gastrointestinal disturbances, and hematologic abnormalities
- Ensure adequate hydration during treatment
Clinical Efficacy
Trimethoprim-sulfamethoxazole remains highly effective for UTIs when the rate of resistance is known or expected to be <20%. Clinical and microbiological cure rates are typically in the 90-100% range. 2
Common Pitfalls to Avoid
Underdosing: Ensure the full weight-based dose is given to achieve therapeutic concentrations.
Inadequate duration: Complete the full 10-14 day course to prevent recurrence and development of resistance.
Failure to obtain culture: Always obtain a urine culture before starting therapy to guide treatment if the empiric choice needs adjustment.
Ignoring local resistance patterns: Consider local resistance patterns when selecting antimicrobial therapy.
Inadequate follow-up: Consider follow-up urine culture 1-2 weeks after completion of therapy for complicated UTIs.
By following these dosing guidelines and monitoring recommendations, Bactrim DS can be an effective treatment option for urinary tract infections in 13-year-old patients.