Recommended Dosage of Bactrim DS for UTI Treatment
The recommended dosage of Bactrim DS (trimethoprim-sulfamethoxazole) for treating a urinary tract infection is one double-strength tablet (160 mg trimethoprim/800 mg sulfamethoxazole) taken orally every 12 hours for 10-14 days for uncomplicated UTIs, with a longer 14-day course specifically recommended for pyelonephritis. 1, 2
Dosing Guidelines by UTI Type
Uncomplicated Cystitis (Lower UTI)
- For uncomplicated cystitis in adults, the standard dose is one Bactrim DS tablet (160/800 mg) every 12 hours for 3 days 1, 3
- In regions with known low resistance rates, a shorter 3-day course may be sufficient for uncomplicated lower UTIs 3, 4
- If local resistance patterns are unknown or high (>20%), consider alternative first-line agents such as nitrofurantoin or fosfomycin 1, 3
Pyelonephritis (Upper UTI)
- For pyelonephritis, one Bactrim DS tablet (160/800 mg) every 12 hours for 14 days is recommended 1, 2
- If using Bactrim when susceptibility is unknown, an initial intravenous dose of a long-acting parenteral antimicrobial (such as 1g ceftriaxone) should be administered before starting oral Bactrim 1
- Bactrim should only be used for pyelonephritis if the uropathogen is known to be susceptible 1
Special Considerations
Resistance Patterns
- Local resistance patterns should guide therapy selection; Bactrim should not be used empirically in areas where E. coli resistance exceeds 20% 1, 3
- If resistance is suspected or confirmed, fluoroquinolones or cephalosporins may be more appropriate alternatives 1
- Always obtain urine culture and susceptibility testing in cases of pyelonephritis, recurrent UTI, or treatment failure 1
Dosing in Renal Impairment
- For patients with creatinine clearance 15-30 mL/min: reduce dose to half the usual regimen 2
- For patients with creatinine clearance <15 mL/min: Bactrim is not recommended 2
Treatment Duration Considerations
- While shorter courses (3 days) may be effective for uncomplicated cystitis in women, longer courses are associated with lower early recurrence rates 5, 4
- Men with UTI generally require longer treatment durations (7-14 days) compared to women with uncomplicated UTI 1, 3
Efficacy and Alternatives
- Bactrim has similar efficacy to fluoroquinolones for uncomplicated UTIs but with fewer adverse effects 6
- Fluoroquinolones should be reserved for more invasive infections due to concerns about collateral damage and resistance 1, 3
- Nitrofurantoin and fosfomycin are appropriate first-line alternatives for uncomplicated cystitis but should not be used for pyelonephritis 1, 3
Common Pitfalls to Avoid
- Avoid using Bactrim empirically in areas with high resistance rates (>20%) 1, 3
- Do not use Bactrim in patients with severe renal impairment (CrCl <15 mL/min) 2
- Never use Bactrim in children under 2 months of age 2
- Avoid underdosing or shortening therapy duration for pyelonephritis, as this can lead to treatment failure and recurrence 1
- Remember that Bactrim should only be used for pyelonephritis when the pathogen is known to be susceptible 1