Dosing of Trimethoprim/Sulfamethoxazole (Bactrim DS) with GFR of 85
For a patient with a GFR of 85 mL/min, the standard dosing regimen for Bactrim DS (trimethoprim/sulfamethoxazole) should be used without any dose adjustment.
Rationale for Standard Dosing
According to the FDA drug label and clinical guidelines, dose adjustments for trimethoprim/sulfamethoxazole are only necessary when renal function is significantly impaired:
- The FDA drug label clearly states that dose adjustments are only required when creatinine clearance falls below 30 mL/min 1
- For patients with creatinine clearance above 30 mL/min, the usual standard regimen is recommended 1
- For patients with creatinine clearance between 15-30 mL/min, half the usual regimen is recommended 1
- For patients with creatinine clearance below 15 mL/min, use is not recommended 1
Dosing Recommendations for Specific Indications
For a patient with GFR of 85 mL/min, the following standard dosing regimens apply:
Urinary Tract Infections
- 1 DS tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for 10-14 days 1
Acute Exacerbations of Chronic Bronchitis
- 1 DS tablet every 12 hours for 14 days 1
Traveler's Diarrhea
- 1 DS tablet every 12 hours for 5 days 1
Pneumocystis jiroveci Pneumonia
- 75-100 mg/kg/day sulfamethoxazole and 15-20 mg/kg/day trimethoprim divided every 6 hours for 14-21 days 1
Pharmacokinetic Considerations
The pharmacokinetics of trimethoprim/sulfamethoxazole support standard dosing for patients with GFR of 85 mL/min:
- Both trimethoprim and sulfamethoxazole disposition are not significantly altered until creatinine clearance is less than 30 mL/min 2
- At higher GFR levels (>30 mL/min), the drugs and their metabolites are cleared efficiently without accumulation that would necessitate dose adjustment
Clinical Pearls and Caveats
- Monitor for adverse effects even in patients with normal renal function, as they can occur independently of drug accumulation
- Common adverse effects include rash, gastrointestinal disturbances, and rarely hematologic abnormalities
- For elderly patients, even with preserved GFR, consider monitoring more closely as they may have higher peak concentrations of trimethoprim compared to younger adults 3
- If the patient is also taking other nephrotoxic medications, more careful monitoring may be warranted even with normal renal function
Conclusion
A patient with a GFR of 85 mL/min has normal renal function for the purposes of trimethoprim/sulfamethoxazole dosing and should receive the standard dosing regimen appropriate for their indication without any renal adjustment.