Bactrim Dosing in Dialysis Patients
For hemodialysis patients, administer one-half the standard Bactrim dose (either 1 single-strength tablet or ½ double-strength tablet) after each dialysis session, three times weekly. 1
Hemodialysis Dosing Regimen
Prophylaxis Dosing
- Single-strength tablets (400mg SMX/80mg TMP): 1 tablet post-dialysis, three times weekly 1
- Double-strength tablets (800mg SMX/160mg TMP): ½ tablet post-dialysis, three times weekly 1
- Always administer immediately after dialysis completion to prevent premature drug removal and ensure adequate therapeutic levels 1, 2
Treatment Dosing for Active Infections
- UTI treatment: 1 double-strength tablet (160mg TMP/800mg SMZ) after each dialysis session, three times weekly 2
- Maintain standard individual dose sizes while extending the dosing interval—never reduce individual doses as this leads to subtherapeutic peak concentrations and treatment failure 2
- Post-dialysis administration is critical because 44% of TMP and 57% of SMZ are removed during a 4-hour dialysis session 3
Peritoneal Dialysis Dosing
For CAPD patients, administer 320mg TMP/1600mg SMZ (2 double-strength tablets) every 48 hours for mild to moderate systemic infections. 4
- Limited data exist for peritoneal dialysis; begin with hemodialysis-equivalent dosing and verify adequacy using serum concentration monitoring 5
- CAPD clearance is minimal (2.27 ml/min for TMP, 1.72 ml/min for SMX), allowing for less frequent dosing compared to hemodialysis 4
Pharmacokinetic Rationale
The dosing adjustments are necessary because:
- Both TMP and SMX accumulate significantly when creatinine clearance falls below 30 mL/min 6
- Hemodialysis removes substantial amounts of both drugs: elimination half-life during dialysis is 6.0 hours for TMP and 3.1 hours for SMZ 3
- Dialysis clearance averages 38 ml/min for TMP and 42 ml/min for SMZ, with extraction ratios of 19% and 21% respectively 3
- The N4-acetyl-SMZ metabolite accumulates proportionally with serum creatinine and may contribute to toxicity 7
Critical Safety Monitoring
Required Monitoring Parameters
- Serum drug concentration monitoring should be considered to ensure adequate absorption without excessive accumulation and to avoid toxicity 5
- Monitor complete blood count for thrombocytopenia and neutropenia, which occur more frequently in dialysis patients receiving TMP-SMX 8, 7
- Thrombocytopenia correlates with higher serum TMP levels and longer treatment duration 7
- Monitor liver function tests, though hepatotoxicity is not clearly related to increased serum concentrations 6
Drug Interactions
- Watch for interactions with anticoagulants (potentiates warfarin), antidiabetic agents, and other hepatically metabolized medications 1
- Maintain adequate fluid intake to prevent crystalluria, though this is less concerning in anuric dialysis patients 1
Common Pitfalls to Avoid
- Never administer before dialysis: Pre-dialysis dosing results in premature drug removal and treatment failure 1, 2
- Do not reduce individual dose sizes: Maintain full per-dose amounts while extending intervals to achieve adequate peak concentrations 2
- Avoid daily dosing in hemodialysis: The three-times-weekly post-dialysis schedule is specifically designed for drug clearance patterns 1, 2
- Do not use standard renal dosing charts: Dialysis-specific guidelines supersede non-dialysis CKD dosing recommendations 2
Clinical Efficacy Evidence
A prospective study in 261 hemodialysis patients demonstrated that daily TMP-SMX prophylaxis (later modified to post-hemodialysis dosing) was highly effective, with 0% infection rates in the prophylaxis group versus 17.4% in the non-prophylaxis group (p<0.001), confirming both efficacy and safety of this approach 8.