Bactrim Dosing in Dialysis Patients
For hemodialysis patients, administer one-half of a double-strength Bactrim tablet (80mg TMP/400mg SMX) or one standard-strength tablet (40mg TMP/200mg SMX) after each dialysis session, three times weekly. 1
Dosing Algorithm for Hemodialysis Patients
Standard Treatment Regimen
- Post-dialysis administration is mandatory to minimize toxicity risk while maintaining therapeutic levels 1
- The dose should be given after completion of each dialysis session, not before or during 1
- For active infections (such as UTI), use one double-strength tablet (160mg TMP/800mg SMX) after each dialysis session, three times weekly 1
Rationale for Dose Reduction
The substantial removal of both components during dialysis necessitates careful dosing:
- Dialysis removes 44% of trimethoprim and 57% of sulfamethoxazole during a standard 4-hour hemodialysis session 2
- Dialyzer clearance averages 38 ml/min for TMP and 42 ml/min for SMX with cuprophane hollow-fiber dialyzers 2
- The elimination half-life during dialysis is 6.0 hours for TMP and 3.1 hours for SMX 2
Critical Dosing Considerations
Do not use standard renal dosing charts for dialysis patients - these apply only to non-dialysis CKD patients and will result in inappropriate dosing 1. The FDA label recommends avoiding use when creatinine clearance is below 15 mL/min 3, but this guidance predates modern dialysis-specific recommendations and should be superseded by the post-dialysis regimen 1.
Prophylaxis Dosing
For PCP prophylaxis in hemodialysis patients:
- Low-dose regimens (<6 single-strength tablets per week) are safer and equally effective compared to standard-dose regimens 4
- The yearly cumulative discontinuation rate due to adverse events was significantly lower with low-dose regimens (12.1% vs 35.6%, P=0.019) 4
- No cases of PCP occurred in either dosing group during observation 4
Common Pitfalls to Avoid
- Never dose before dialysis - this results in immediate drug removal and subtherapeutic levels 1
- Avoid daily dosing in dialysis patients - accumulation of metabolites occurs and increases toxicity risk without improving efficacy 2
- Do not extrapolate from peritoneal dialysis data - peritoneal dialysance is negligible (5.1 ml/min for TMP, 1.2 ml/min for SMX), requiring different dosing strategies 5
Monitoring Parameters
- Maintain adequate fluid intake to prevent crystalluria, though this is less concerning in anuric dialysis patients 6
- Watch for hypersensitivity reactions, blood dyscrasias, and hepatotoxicity, which may occur more frequently in dialysis patients 7
- Consider drug interactions with anticoagulants, antidiabetic agents, and other medications metabolized hepatically 6