Bactrim Dosing for Uncomplicated UTI
For adult women with uncomplicated cystitis, prescribe Bactrim DS (160 mg trimethoprim/800 mg sulfamethoxazole) one double-strength tablet twice daily for 3 days. 1
Standard Dosing by Patient Population
Women with Uncomplicated Cystitis
- Dose: 160 mg trimethoprim/800 mg sulfamethoxazole (one double-strength tablet) twice daily 1
- Duration: 3 days 1, 2
- Clinical cure rates: 90-100% when the pathogen is susceptible 1
- Bacterial eradication rates: 91-100% for susceptible organisms 1
Men with UTI
- Dose: 160 mg trimethoprim/800 mg sulfamethoxazole (one double-strength tablet) twice daily 1
- Duration: 7 days (longer than women due to anatomical differences) 1
Uncomplicated Pyelonephritis
- Dose: 160 mg trimethoprim/800 mg sulfamethoxazole (one double-strength tablet) twice daily 1
- Duration: 14 days 1
- Critical caveat: Only use if susceptibility is confirmed 1
Critical Resistance Threshold
Do not use Bactrim empirically when local E. coli resistance exceeds 20%. 1
- When resistance is below 20%, clinical cure rates remain 84% for susceptible organisms 1
- When organisms are resistant, cure rates plummet to only 41-54% 1
- Treatment failures outweigh benefits when resistance thresholds are exceeded 1
When to Avoid Empiric Bactrim Use
Avoid Bactrim in patients with:
- Recent trimethoprim-sulfamethoxazole use within the preceding 3-6 months 1
- Travel outside the United States within the preceding 3-6 months 1
- Pregnancy in the last trimester 1
- Areas where local resistance data shows >20% E. coli resistance 1
Alternative First-Line Agents
When Bactrim cannot be used due to resistance or contraindications:
- Nitrofurantoin monohydrate/macrocrystals: 100 mg twice daily for 5-7 days (clinical cure rate 88-93%) 3
- Fosfomycin trometamol: 3 g single dose 1, 2
- Pivmecillinam: 400 mg twice daily for 5 days (where available) 1
Important Clinical Caveats
- Each additional day of antibiotic treatment beyond the recommended 3-day duration carries a 5% increased risk for antibiotic-associated adverse events without additional benefits 1
- Hospital antibiograms often overestimate community resistance rates; local outpatient surveillance data is more accurate for guiding empiric therapy 1
- Common side effects include rash, urticaria, nausea, vomiting, and hematologic abnormalities 1
- Fluoroquinolones should be reserved for pyelonephritis rather than simple cystitis, despite low resistance rates, due to concerns about collateral damage 1