What is the recommended dosing of Bactrim (trimethoprim-sulfamethoxazole) for an uncomplicated urinary tract infection (UTI)?

Bactrim Dosing for Uncomplicated UTI

Primary Recommendation

For uncomplicated UTI in women, prescribe Bactrim DS (160 mg trimethoprim/800 mg sulfamethoxazole) one tablet twice daily for 3 days. 1

Dosing by Patient Population

Women with Uncomplicated Cystitis

• Standard dose: Bactrim DS (160/800 mg) twice daily for 3 days 1
• This short-course regimen achieves 90-100% clinical cure rates when the pathogen is susceptible 1
• Bacterial eradication rates are similarly excellent at 91-100% 1

Men with UTI

• Extended duration required: Bactrim DS (160/800 mg) twice daily for 7 days 1
• Men require longer treatment courses than women due to anatomical differences and higher risk of complicated infection 1

Complicated UTI or Pyelonephritis

• Bactrim DS twice daily for 14 days if susceptibility is confirmed 1
• The FDA label indicates 10-14 days for standard UTI treatment 2

Critical Prescribing Restrictions

Do not use Bactrim empirically if local E. coli resistance exceeds 20% 1

When to Avoid Bactrim:

• Local resistance data shows >20% E. coli resistance to trimethoprim-sulfamethoxazole 1
• Patient used Bactrim in the preceding 3-6 months 1
• Recent travel outside the United States within 3-6 months 1
• Last trimester of pregnancy 1

Resistance Impact on Efficacy:

• When organisms are susceptible: 84-100% cure rate 1
• When organisms are resistant: Only 41-54% cure rate 1
• This dramatic drop in efficacy makes resistance screening essential 1

Alternative First-Line Agents

If Bactrim cannot be used due to resistance or contraindications:

• Nitrofurantoin monohydrate/macrocrystals: 100 mg twice daily for 5 days (90-93% clinical cure rate) 3
• Fosfomycin trometamol: 3 g single dose 1
• Pivmecillinam: 400 mg twice daily for 5 days (where available) 1

These alternatives maintain resistance rates generally below 10% across most regions 1

Important Clinical Caveats

Antibiogram Interpretation:

• Hospital antibiograms often overestimate community resistance rates 1
• Use local outpatient surveillance data when available for more accurate empiric therapy guidance 1

Duration Considerations:

• Each additional day of treatment beyond recommended duration carries a 5% increased risk of antibiotic-associated adverse events without additional benefit 1
• The 3-day regimen for women has equivalent efficacy to longer courses with fewer side effects 1

Common Side Effects:

• Rash and urticaria 1
• Nausea and vomiting 1
• Hematologic abnormalities 1

Renal Dosing Adjustment:

• Creatinine clearance 15-30 mL/min: Use half the usual regimen 2
• Creatinine clearance <15 mL/min: Use not recommended 2

Pediatric Dosing (≥2 months of age)

• 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided into two doses every 12 hours for 10 days 2
• Not recommended for children less than 2 months of age 2