Bactrim Dosage for Uncomplicated UTI
For uncomplicated urinary tract infections in adults, the recommended dose of Bactrim (trimethoprim/sulfamethoxazole) is one double-strength tablet (160/800 mg) or two regular-strength tablets (80/400 mg) taken orally every 12 hours for 3 days. 1, 2, 3
Dosing Recommendations
Adult Dosing
- First-line regimen: 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3 days 1
- While the FDA label mentions 10-14 days 2, 3, clinical guidelines now recommend the shorter 3-day course for uncomplicated UTIs as it provides similar efficacy with fewer adverse events 1
Special Populations
- Renal impairment:
Pediatric Dosing
- For children ≥2 months: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided into two doses given every 12 hours for 10 days 2, 3
- Not recommended for infants under 2 months of age 2, 3
Clinical Considerations
Efficacy and Treatment Duration
- Short-course therapy (3 days) for trimethoprim-sulfamethoxazole is as effective as longer treatment for uncomplicated UTIs, with fewer adverse events 1
- Older studies showed cure rates of 87% with 10-day courses and 76% with single-dose therapy 4, but current guidelines favor the 3-day regimen as the optimal balance between efficacy and side effect risk
Resistance Considerations
- Trimethoprim-sulfamethoxazole should be used as first-line therapy only in areas where local resistance rates are below 20% 5
- If local resistance patterns are unknown or high (>20%), consider alternative first-line agents such as nitrofurantoin or fosfomycin 1
Follow-up Recommendations
- No post-treatment urinalysis or urine culture is required if symptoms resolve 1
- If symptoms persist or recur within 2 weeks, obtain urine culture and antibiogram, and consider treatment with an alternative agent for 7 days 1
Common Pitfalls and Caveats
- Resistance concerns: Local resistance patterns significantly impact treatment success. In areas with high resistance, alternative agents should be considered
- Treatment duration: Despite FDA labeling suggesting 10-14 days, current guidelines recommend 3 days for uncomplicated UTIs to reduce adverse effects while maintaining efficacy
- Adverse effects: Monitor for rash, GI disturbances, and rare but serious reactions including Stevens-Johnson syndrome and bone marrow suppression
- Contraindications: Avoid in patients with sulfa allergies, G6PD deficiency, severe renal impairment, or pregnancy near term
Remember that treatment failure may occur if the causative organism is resistant to trimethoprim-sulfamethoxazole, so clinical response should be monitored and therapy adjusted accordingly.