Bactrim (TMP-SMX) Dosing for Pyelonephritis
For pyelonephritis, trimethoprim-sulfamethoxazole (TMP-SMX) should be dosed at 160/800 mg (one double-strength tablet) twice daily for 14 days when the causative organism is known to be susceptible. 1, 2
Dosing Recommendations
Standard Dosing
- Adults: 160/800 mg (one double-strength tablet) twice daily for 14 days 1, 2
- Duration: 14 days is the FDA-approved duration for pyelonephritis 1
Special Populations
Renal Impairment
- CrCl >30 mL/min: Standard regimen
- CrCl 15-30 mL/min: Half the usual regimen (80/400 mg twice daily)
- CrCl <15 mL/min: Use not recommended 2
Pregnant Women
- Pregnant women with pyelonephritis require inpatient management, especially those with fever, severe flank pain, nausea/vomiting, signs of sepsis, or inability to tolerate oral medications 3
Initial Parenteral Therapy Considerations
For patients with moderate to severe pyelonephritis, consider:
- Initial dose of a long-acting parenteral antimicrobial (e.g., ceftriaxone 1g IV once) before starting oral TMP-SMX 1, 3
- This approach is particularly important in regions with high resistance rates to TMP-SMX
Efficacy and Resistance Considerations
- TMP-SMX is highly efficacious for pyelonephritis when the causative organism is susceptible 1
- Only use TMP-SMX if local resistance rates for uropathogens causing acute uncomplicated cystitis do not exceed 20% 1
- Always obtain a urine culture before starting therapy for pyelonephritis 3
Alternative Regimens
If TMP-SMX cannot be used due to resistance or contraindications:
- Fluoroquinolones: Ciprofloxacin 500-750 mg twice daily for 7 days or levofloxacin 750 mg once daily for 5-7 days 1, 3
- These are preferred in regions with high TMP-SMX resistance
Monitoring
- Assess clinical response within 48-72 hours of initiating therapy 3
- Consider repeat urine culture 1-2 weeks after completion of therapy 3
Important Caveats
- TMP-SMX has been shown to be less effective than fluoroquinolones for pyelonephritis when resistance is present 4
- In a comparative study, a 7-day ciprofloxacin regimen demonstrated superior bacteriologic and clinical cure rates compared to a 14-day TMP-SMX regimen (99% vs 89% bacteriologic cure) 4
- Recent evidence suggests that a 7-day course of TMP-SMX may be as effective as a 7-day course of ciprofloxacin for susceptible organisms, but the FDA-approved duration remains 14 days 5, 2
Remember that empiric therapy should always be guided by local resistance patterns and adjusted based on culture and susceptibility results.