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

Bactrim Dosing for Uncomplicated UTI

For uncomplicated UTI in women, the recommended dose is Bactrim DS (trimethoprim 160 mg/sulfamethoxazole 800 mg) one double-strength tablet twice daily for 3 days, but for men, extend treatment to 7 days. 1, 2, 3

Standard Dosing by Patient Population

Women with Uncomplicated Cystitis

• Bactrim DS 160/800 mg twice daily for 3 days is the standard regimen 1, 2, 3
• This 3-day course achieves clinical cure rates of 90-100% when organisms are susceptible 2
• Bacterial eradication rates reach 91-100% for susceptible pathogens 2

Men with UTI

• Bactrim DS 160/800 mg twice daily for 7 days is required 1, 2, 4
• Men require longer treatment duration because male UTIs are considered complicated 4
• The 3-day regimen used in women is inadequate for male patients 4

Critical Resistance Threshold

Only use Bactrim empirically when local E. coli resistance is below 20% 1, 2

When to Avoid Bactrim

• Local resistance data shows >20% E. coli resistance 2
• Patient used trimethoprim-sulfamethoxazole in the preceding 3-6 months 2
• Recent travel outside the United States within 3-6 months 2
• When resistance is present, clinical cure rates drop dramatically from 90-100% to only 41-54% 2

Renal Dose Adjustments

Creatinine Clearance-Based Dosing 3

• CrCl >30 mL/min: Standard dose (1 DS tablet twice daily) 3
• CrCl 15-30 mL/min: Reduce to half-dose (1 single-strength tablet or half DS tablet) 3
• CrCl <15 mL/min: Use not recommended 3

Monitoring in Renal Impairment 4

• Obtain baseline creatinine clearance before initiating therapy 4
• Monitor electrolytes regularly, as trimethoprim can cause hyperkalemia 4
• Check serum creatinine and BUN 2-3 times weekly during therapy 4
• Ensure adequate hydration (at least 1.5 liters daily) to prevent crystalluria 4

Pregnancy Considerations

• Avoid in the first trimester (trimethoprim alone) 1, 4
• Avoid in the last trimester (trimethoprim-sulfamethoxazole combination) 1, 4

Alternative First-Line Agents

When Bactrim is inappropriate due to resistance or contraindications, consider 1, 2:

• Fosfomycin trometamol: 3 g single dose 1
• Nitrofurantoin: 100 mg twice daily for 5 days 1
• Pivmecillinam: 400 mg three times daily for 3-5 days 1

These alternatives maintain excellent activity with resistance rates generally below 10% 2

Common Pitfalls to Avoid

• Do not use the 3-day regimen for men—this is inadequate treatment and requires 7 days minimum 4
• Do not fail to adjust dose in renal impairment (CrCl <30 mL/min)—this significantly increases toxicity risk 4, 3
• Do not use empirically when local resistance exceeds 20%—treatment failures will outweigh benefits 2
• Do not perform routine post-treatment cultures in asymptomatic patients—this is not indicated 1

When to Obtain Urine Culture

Urine culture is recommended in the following situations 1:

• Suspected acute pyelonephritis
• Symptoms that do not resolve or recur within 4 weeks after completion of treatment
• Women who present with atypical symptoms
• Pregnant women

Treatment Failure Management

For patients whose symptoms do not resolve by end of treatment or recur within 2 weeks 1:

• Perform urine culture and antimicrobial susceptibility testing
• Assume the infecting organism is not susceptible to the originally used agent
• Retreat with a 7-day regimen using another agent