Trimethoprim-Sulfamethoxazole Dosing for Dialysis Patients with UTI
For patients on hemodialysis with a urinary tract infection, trimethoprim-sulfamethoxazole should be dosed at half the standard dose (one single-strength tablet daily or one double-strength tablet three times weekly) administered after each dialysis session. 1
Dosing Recommendations
Standard Dosing
- Normal renal function: 1 double-strength tablet (160mg/800mg) every 12 hours
- Duration: 7-14 days for complicated UTIs 2
Dialysis Patient Dosing
- Hemodialysis patients:
- ½ standard dose (1 single-strength tablet daily or 1 double-strength tablet three times weekly)
- Administer scheduled dose after each dialysis session 1
- Peritoneal dialysis patients:
- Similar adjustments apply, with dose administered after peritoneal dialysis
Pharmacokinetic Considerations
Trimethoprim-sulfamethoxazole is primarily eliminated by the kidneys through both glomerular filtration and tubular secretion 3. In patients with renal impairment:
- Mean serum half-lives of both components are significantly increased
- Approximately 84.5% of sulfamethoxazole and 66.8% of trimethoprim are normally excreted in urine within 72 hours 3
- Reduced renal clearance in dialysis patients necessitates dose adjustment to prevent drug accumulation and toxicity
Monitoring Recommendations
- Monitor for signs of adverse effects, particularly:
- Hyperkalemia (due to trimethoprim's potassium-sparing effects)
- Increased serum creatinine (trimethoprim can compete with creatinine for tubular secretion)
- Acute kidney injury, which occurs in approximately 11.2% of patients on TMP-SMX 4
- Bone marrow suppression (monitor CBC)
Clinical Considerations
- Assess culture and sensitivity results to confirm appropriate antibiotic choice
- Consider alternative agents if the patient has:
- Sulfa allergy
- Severe renal impairment with GFR <15 mL/min (where alternative agents may be preferred)
- History of adverse reactions to TMP-SMX
Alternative Options for Dialysis Patients
If TMP-SMX is contraindicated or not tolerated, consider:
- Ciprofloxacin: 250-500 mg after each dialysis 1
- Levofloxacin: 250 mg after each dialysis 1
- Cephalexin: Dose adjusted based on dialysis schedule
Important Cautions
- Avoid nitrofurantoin in dialysis patients (ineffective with GFR <30 mL/min and potentially toxic) 2
- TMP-SMX may increase risk of hyperkalemia in dialysis patients
- Monitor for drug interactions, particularly with warfarin and methotrexate
- Patients with both diabetes and renal impairment are at higher risk for adverse effects 4
The recommendation for half-dose TMP-SMX in dialysis patients with administration after dialysis is well-established in guidelines and supported by pharmacokinetic principles to optimize efficacy while minimizing toxicity.