What is the recommended dosage of Bactrim (sulfamethoxazole and trimethoprim) for treating uncomplicated urinary tract infections?

Bactrim Dosing for Uncomplicated Urinary Tract Infections

For uncomplicated UTIs in women, prescribe Bactrim DS (160 mg trimethoprim/800 mg sulfamethoxazole) one tablet twice daily for 3 days, but only when local E. coli resistance rates are below 20%. 1

Standard Dosing by Patient Population

Women with Uncomplicated Cystitis

• Bactrim DS: 1 double-strength tablet (160/800 mg) twice daily for 3 days 1, 2
• This short-course regimen achieves 90-100% clinical cure rates when organisms are susceptible 1
• Bacterial eradication rates reach 91-100% for susceptible pathogens 1

Men with UTI

• Bactrim DS: 1 double-strength tablet (160/800 mg) twice daily for 7 days 1
• Men require longer treatment duration than women due to anatomical differences and higher risk of prostatic involvement 1

Complicated UTI or Pyelonephritis

• Bactrim DS: 1 double-strength tablet twice daily for 14 days 1, 2
• Use only if susceptibility is confirmed by culture 1

Critical Resistance Threshold

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

When to Avoid Bactrim

• Local resistance data shows >20% E. coli resistance 1
• Patient used trimethoprim-sulfamethoxazole in the preceding 3-6 months 1
• Recent travel outside the United States within 3-6 months 1
• When resistance is present, clinical cure rates drop dramatically from 84% to only 41% 1

Hospital Antibiogram Caveat

• Hospital antibiograms often overestimate community resistance rates 1
• Local outpatient surveillance data is more accurate for guiding empiric therapy 1

Alternative First-Line Agents

When Bactrim cannot be used due to resistance or allergy:

• Nitrofurantoin monohydrate/macrocrystals: 100 mg twice daily for 5 days 3

  • Clinical cure rate: 90% (equivalent to Bactrim) 3
  • Bacterial cure rate: 92% 3
  • Resistance rates generally below 10% across all regions 1

• Fosfomycin trometamol: 3 g single dose 1, 3

  • Slightly lower efficacy than nitrofurantoin but convenient single-dose option 3

• Pivmecillinam: 400 mg twice daily for 5 days (where available) 3

Common Side Effects and Safety

• Rash, urticaria, nausea, vomiting, and hematologic abnormalities are common with Bactrim 1
• Each additional day of treatment beyond recommended duration carries a 5% increased risk for antibiotic-associated adverse events without additional benefits 1
• Avoid in the last trimester of pregnancy 1

Renal Dosing Adjustments

For patients with impaired renal function 2:

• Creatinine clearance >30 mL/min: Standard dosing
• Creatinine clearance 15-30 mL/min: Half the usual regimen
• Creatinine clearance <15 mL/min: Use not recommended