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

Bactrim Dosing for Uncomplicated UTI

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

Standard Dosing by Patient Population

Women with Uncomplicated Cystitis

• Bactrim DS 160/800 mg twice daily for 3 days is the recommended regimen 1
• This short-course therapy achieves 90-100% clinical cure rates when the pathogen is susceptible 1
• Bacterial eradication rates reach 91-100% for susceptible organisms 1

Men with UTI

• Bactrim DS 160/800 mg twice daily for 7 days is required for male patients 1, 2
• The standard 3-day regimen used in women is inadequate for men—do not use it 2
• Some guidelines recommend extending to 7-14 days depending on clinical response 2

Critical Prescribing Restrictions

When NOT to Use Bactrim Empirically

Only prescribe Bactrim when local E. coli resistance is documented to be <20% 1

Avoid empiric Bactrim in patients with:

• Recent trimethoprim-sulfamethoxazole use within the preceding 3-6 months 1
• Recent travel outside the United States within the preceding 3-6 months 1
• Last trimester of pregnancy (European Association of Urology contraindication) 2

Resistance Impact on Efficacy

• When organisms are susceptible: 84-100% cure rate 1
• When organisms are resistant: cure rates plummet to 41-54% 1
• This dramatic difference makes resistance screening essential before prescribing 1

Renal Dose Adjustments

Dosing by Creatinine Clearance

Per FDA labeling 3:

• CrCl >30 mL/min: Standard dose (1 DS tablet twice daily)
• CrCl 15-30 mL/min: Reduce to half-dose (1 single-strength tablet or half DS tablet)
• CrCl <15 mL/min: Use not recommended

Monitoring in Renal Impairment

• Check baseline creatinine clearance before initiating therapy 2
• Monitor electrolytes regularly as trimethoprim can cause hyperkalemia 2
• Ensure adequate hydration (at least 1.5 liters daily) to prevent crystalluria 2

Alternative First-Line Agents

When Bactrim cannot be used due to resistance or contraindications, the Infectious Diseases Society of America and European Association of Urology recommend 1, 2:

• Nitrofurantoin 100 mg twice daily for 5 days (90% clinical cure rate) 1
• Fosfomycin trometamol 3g single dose 2
• Pivmecillinam 400 mg three times daily for 3-5 days 2

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

Common Prescribing Pitfalls

Duration Errors

• Do not extend therapy beyond 3 days in women without clinical indication—each additional day carries a 5% increased risk for antibiotic-associated adverse events without additional benefit 1
• Do not use 3-day regimens in men—this is the most common error 2

Resistance Underestimation

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

Pregnancy Considerations

• Avoid in the last trimester due to potential complications 2
• Trimethoprim should not be used in the first trimester of pregnancy 2

Expected Adverse Effects

Common side effects include 1:

• Rash and urticaria
• Nausea and vomiting
• Hematologic abnormalities

These occur in approximately 21.8% of patients on combination therapy, compared to lower rates with alternative agents 4