Recommended Dosage of Trimethoprim-Sulfamethoxazole for UTIs
For uncomplicated UTIs in adults, the recommended dose of trimethoprim-sulfamethoxazole is 160/800 mg (one double-strength tablet) twice daily for 3 days. 1
Dosing Recommendations by UTI Type
Uncomplicated UTIs
- Adults: 160/800 mg (1 double-strength tablet) twice daily for 3 days 1
- Alternative FDA-approved regimen: 160/800 mg (1 double-strength tablet) every 12 hours for 10-14 days 2
Complicated UTIs/Pyelonephritis
- Adults: 160/800 mg (1 double-strength tablet) twice daily for 14 days 1
- If susceptibility is unknown, combine with an initial IV dose of a long-acting parenteral antimicrobial (e.g., 1g ceftriaxone) 1
Pediatric Dosing
- Children ≥2 months: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided into two doses given every 12 hours for 10 days 2
- Weight-based dosing:
- 22 kg (10-20 lb): 1 tablet every 12 hours
- 44 kg (20-30 lb): 1½ tablets every 12 hours
- 66 kg (30-40 lb): 2 tablets or 1 DS tablet every 12 hours 2
Special Considerations
Renal Impairment
- CrCl >30 mL/min: Standard regimen
- CrCl 15-30 mL/min: Half the usual regimen
- CrCl <15 mL/min: Not recommended 2
Hemodialysis Patients
- Half the standard dose (one single-strength tablet daily or one double-strength tablet three times weekly) administered after each dialysis session 1
Important Clinical Considerations
Efficacy Considerations
- TMP-SMX should only be used when local resistance rates are below 20% and the patient has no history of recent TMP-SMX use or international travel 1
- For uncomplicated UTIs, 3-day regimens are as effective as longer courses while reducing side effects and resistance development 1
Monitoring
- Evaluate clinical response within 48-72 hours of initiating therapy
- No routine follow-up urine culture needed in patients who respond to therapy
- Follow-up urine culture should be performed 7 days after completing treatment to assess for persistent or recurrent bacteriuria 1
Adverse Effects
- Monitor for hyperkalemia, increased serum creatinine, acute kidney injury, and bone marrow suppression 1
- Serious adverse reactions occur less frequently with shorter treatment courses (8.5% with single-dose vs. 15% with 10-day regimens) 3
Alternative Treatments
- When TMP-SMX is not appropriate due to resistance concerns, consider:
- Nitrofurantoin 100 mg twice daily for 5 days
- Fosfomycin trometamol 3 g single dose 1
Common Pitfalls to Avoid
- Using TMP-SMX in areas with high resistance rates (>20%)
- Prescribing prolonged courses unnecessarily, which increases risk of side effects without improving outcomes
- Treating asymptomatic bacteriuria, which increases antibiotic resistance without clinical benefit
- Failing to obtain a urine culture before treatment, especially in recurrent cases 1