TMP/SMX Dosing for Recurrent UTI Prophylaxis
For recurrent UTI prophylaxis in women, use TMP/SMX 40mg/200mg (half of a single-strength tablet) once daily at bedtime, or alternatively, the same dose three times weekly. 1
Prophylactic Dosing Regimens
Daily Prophylaxis
- The standard prophylactic dose is one double-strength tablet (160mg TMP/800mg SMX) once daily for adults requiring continuous prophylaxis 2
- Lower-dose regimens using 40mg TMP/200mg SMX once nightly have demonstrated excellent efficacy with an infection rate of only 0.1 per patient-year 1
Intermittent Prophylaxis
- Thrice-weekly dosing (40mg TMP/200mg SMX three times per week at bedtime) is highly effective for recurrent UTI prevention, maintaining suppression of periurethral and anal canal colonization with Enterobacteriaceae 1
- This regimen resulted in only 2 breakthrough infections during 21.3 cumulative patient-years of prophylaxis 1
Treatment Dosing (For Acute Episodes)
Uncomplicated Cystitis
- For acute uncomplicated UTI in women: 160mg TMP/800mg SMX (one double-strength tablet) twice daily for 3 days 3
- This 3-day regimen achieves 90-100% clinical cure rates when organisms are susceptible 3
- The FDA-approved duration for uncomplicated UTI is 10-14 days, but guideline societies strongly recommend the shorter 3-day course based on superior evidence 2
Men with UTI
- Men require 160mg TMP/800mg SMX twice daily for 7 days due to higher risk of prostatic involvement 3
Complicated UTI or Pyelonephritis
- For pyelonephritis: 160mg TMP/800mg SMX twice daily for 14 days, but only after confirming susceptibility 3
Critical Resistance Threshold
Do not use TMP/SMX empirically if local E. coli resistance exceeds 20%, as efficacy plummets from 84% to only 41-54% when organisms are resistant 3
Additional Risk Factors for Resistance
- Recent TMP/SMX use within the preceding 3-6 months 3
- International travel within the preceding 3-6 months 3
Pediatric Dosing
- Children ≥2 months: 40mg/kg SMX and 8mg/kg TMP per 24 hours, divided into two doses every 12 hours for 10 days 2
- For prophylaxis in children: 750mg/m²/day SMX with 150mg/m²/day TMP given in divided doses twice daily on 3 consecutive days per week 2
Renal Dosing Adjustments
- CrCl >30 mL/min: Use standard dosing 2
- CrCl 15-30 mL/min: Reduce dose by 50% 2
- CrCl <15 mL/min: Use not recommended 2
Alternative First-Line Agents When TMP/SMX Cannot Be Used
- Nitrofurantoin monohydrate/macrocrystals 100mg twice daily for 5 days achieves 90% clinical cure and 92% bacterial cure rates 3
- Fosfomycin trometamol 3g single dose offers convenient single-dose therapy with equivalent efficacy 3
Common Pitfalls
- Avoid using TMP/SMX for prophylaxis without first documenting local resistance patterns - hospital antibiograms often overestimate community resistance 3
- Do not continue prophylaxis indefinitely without reassessment - in one study, 21 of 32 patients had recurrent infection within 6 months of stopping prophylaxis (mean 2.6 months), indicating the need for ongoing evaluation 1
- Resistance development during prophylaxis is uncommon - only 1 patient developed transient colonization with resistant E. coli during thrice-weekly prophylaxis 1