Bactrim DS Dosage for UTI in Adults
For uncomplicated urinary tract infections in adults, the recommended dosage of Bactrim DS (trimethoprim-sulfamethoxazole) is one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for 3-5 days. 1, 2
Dosage Details
- Standard dosage: One Bactrim DS tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours
- Treatment duration:
Efficacy Evidence
Trimethoprim-sulfamethoxazole remains highly effective for uncomplicated UTIs with:
- 90-100% early clinical cure rates 3
- 90-91% early bacterial cure rates 3
- 79-84% late clinical cure rates 3
Important Considerations
Resistance Patterns
- Only use if local E. coli resistance is <20% 1
- Significantly lower cure rates with resistant organisms (41-54% vs 84-88% for susceptible organisms) 3
Patient-Specific Factors
- Renal impairment: Dose adjustment required 2
- CrCl >30 mL/min: Standard regimen
- CrCl 15-30 mL/min: Half the usual regimen
- CrCl <15 mL/min: Not recommended
Monitoring
- Clinical improvement typically occurs within 48-72 hours 1
- Routine post-treatment cultures not indicated for asymptomatic patients 1
- If symptoms persist beyond 72 hours or recur within 2 weeks, obtain urine culture and susceptibility testing 1
Alternative First-Line Options
If Bactrim DS is contraindicated or resistance is suspected:
- Nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days 3, 1
- Fosfomycin trometamol (single dose) 1
Common Pitfalls to Avoid
Overtreatment: Longer treatment durations (10 days vs 3-5 days) do not improve outcomes for uncomplicated UTIs but increase adverse effects (28% vs 5-9%) 4
Ignoring resistance patterns: Treatment failure is significantly more likely when the pathogen is resistant to trimethoprim-sulfamethoxazole 3
Unnecessary follow-up testing: Routine post-treatment cultures are not indicated in asymptomatic patients 1
Missing upper tract infection: Pyelonephritis requires longer treatment (7-14 days) 1, 2
While the FDA label mentions a 10-14 day course 2, more recent guidelines from the Infectious Diseases Society of America and European Association of Urology recommend shorter 3-5 day courses for uncomplicated UTIs 3, 1, which have been shown to be equally effective with fewer side effects.