Bactrim (Trimethoprim-Sulfamethoxazole) Dosing for a 15-Year-Old with Recurrent UTIs
For a 15-year-old patient weighing 103 pounds (46.7 kg) with recurrent UTIs, the recommended dose of Bactrim is 8-12 mg/kg/day of the trimethoprim component divided into two doses every 12 hours for 10-14 days. 1, 2
Specific Dosing Calculation
Based on the patient's weight of 103 pounds (46.7 kg):
- Trimethoprim component: 8-12 mg/kg/day
- At 8 mg/kg/day: 46.7 kg × 8 mg/kg = 373.6 mg/day
- At 12 mg/kg/day: 46.7 kg × 12 mg/kg = 560.4 mg/day
Recommended Dosing Options:
- 1 double-strength tablet (160 mg TMP/800 mg SMX) every 12 hours for 10-14 days 1, 2
- OR
- 2 regular-strength tablets (80 mg TMP/400 mg SMX per tablet) every 12 hours for 10-14 days 2
Treatment Duration
- For uncomplicated UTIs: 10-14 days of treatment is recommended 1, 2
- For recurrent UTIs: Complete the full 14-day course to ensure complete eradication 1
Monitoring Recommendations
- Evaluate clinical response within 48-72 hours of initiating therapy
- Consider follow-up urine culture 7 days after completing treatment to assess for persistent or recurrent bacteriuria, especially important in recurrent cases 1
- Monitor for adverse effects:
- Skin rashes
- Gastrointestinal disturbances
- Signs of bone marrow suppression
- Hyperkalemia
- Changes in renal function 1
Important Considerations
- Ensure the patient has normal renal function before prescribing this dose
- If renal function is impaired (creatinine clearance 15-30 mL/min), reduce the dose by 50% 2
- If creatinine clearance is below 15 mL/min, Bactrim is not recommended 2
- Obtain a urine culture before initiating treatment to confirm susceptibility, especially important in recurrent cases 1
- Consider local resistance patterns - Bactrim should only be used when local resistance rates are below 20% 1
Prevention of Recurrent UTIs
For patients with frequent recurrences after this treatment course, prophylactic options include:
- Low-dose Bactrim (one single-strength tablet daily or three times weekly) 1
- Increased fluid intake (additional 1.5L daily) 1
- Post-urination hygiene measures 1
- Post-coital single dose if UTIs are related to sexual activity 1
This dosing regimen aligns with current guidelines for treating UTIs in adolescents and will provide effective coverage while minimizing the risk of adverse effects.