Bactrim Dosing in Renal Impairment (Creatinine 57 µmol/L)
For a patient with a creatinine of 57 µmol/L (approximately 0.64 mg/dL, indicating normal renal function), use standard Bactrim dosing without adjustment. 1
Creatinine Interpretation and Dosing Decision
- A creatinine of 57 µmol/L converts to approximately 0.64 mg/dL, which corresponds to a creatinine clearance well above 30 mL/min in most patients 1
- Standard dosing applies: 1 double-strength tablet (160/800 mg) twice daily for most indications, or 2 single-strength tablets twice daily 1
- Dose adjustment is only required when creatinine clearance falls below 30 mL/min 2, 1
Standard Dosing Regimens by Indication
For urinary tract infections and shigellosis:
- 1 double-strength tablet (160/800 mg) every 12 hours for 10-14 days (UTI) or 5 days (shigellosis) 1
For acute exacerbations of chronic bronchitis:
- 1 double-strength tablet every 12 hours for 14 days 1
For Pneumocystis jirovecii pneumonia treatment:
- 75-100 mg/kg sulfamethoxazole and 15-20 mg/kg trimethoprim per 24 hours, divided every 6 hours for 14-21 days 1
For PCP prophylaxis:
- 1 double-strength tablet daily 1
Renal Dosing Guidelines (When Needed)
The FDA-approved dosing adjustments apply only when renal function is significantly impaired 1:
- CrCl >30 mL/min: Standard dosing regimen 2, 1
- CrCl 15-30 mL/min: Reduce dose by 50% (half the usual regimen) 2, 1
- CrCl 5-15 mL/min: Further reduction to 500 mg daily or 500 mg three times weekly after dialysis 2
- CrCl <15 mL/min: Use not recommended per FDA labeling 1
Important Clinical Considerations
Drug interactions that increase hyperkalemia risk:
- ACE inhibitors, ARBs, and MRAs significantly increase potassium levels when combined with trimethoprim 2
- Monitor potassium closely, especially in patients on these medications 2
Nephrotoxicity risk factors:
- Trimethoprim/sulfamethoxazole can cause acute kidney injury in 5.8-11.2% of patients, particularly those with hypertension and diabetes 3
- AKI typically manifests as intrinsic renal impairment rather than interstitial nephritis 3
- Most cases resolve promptly after discontinuation 3
- Baseline and follow-up creatinine monitoring is essential for courses ≥6 days 3, 4
Timing with dialysis (if applicable):
- Administer after dialysis to prevent premature drug removal and facilitate directly observed therapy 2, 5
Monitoring Parameters
- Check baseline renal function and electrolytes before initiation 2
- Recheck creatinine and potassium 1-2 weeks after starting therapy, especially in high-risk patients 2, 3
- For prolonged courses (>6 days), monitor renal function periodically 3
- Discontinue immediately if unexplained creatinine elevation occurs 3
Common Pitfalls to Avoid
- Do not assume dose reduction is needed based solely on creatinine level—calculate actual creatinine clearance, as this patient's creatinine of 57 µmol/L is normal 1, 6
- Avoid concurrent NSAIDs and high-potassium salt substitutes, which increase toxicity risk 2
- Do not overlook drug accumulation in elderly patients—even with "normal" creatinine, age-related renal decline may warrant closer monitoring 4
- Recognize that trimethoprim alone can increase serum creatinine by 10-20% through competitive inhibition of tubular secretion without true renal injury 3, 4