Renal Dose of Fosfomycin in Hemodialysis Patients
For patients on hemodialysis three times weekly, administer fosfomycin 2 grams IV immediately after each dialysis session (three times per week), never reducing the dose despite renal impairment. 1
Dosing Strategy
The fundamental principle is post-dialysis administration of the full 2-gram dose to prevent premature drug removal while maintaining concentration-dependent bactericidal activity. 1
Key Dosing Parameters:
- Dose: 2 grams IV (never reduce) 1, 2
- Frequency: After each hemodialysis session (three times weekly) 1
- Timing: Within 30 minutes of dialysis completion 1
- Route: Intravenous administration 2
Pharmacokinetic Rationale
Fosfomycin is heavily dialyzed (70-80% removal) by hemodialysis membranes, with dialyzer clearance of approximately 103 ml/min. 3, 2, 4 When administered before dialysis, the drug is actively eliminated during the session, but when given post-dialysis, plasma levels remain therapeutic (60 mg/L at 44 hours) with a prolonged half-life of 48.8 hours between sessions. 2
The entire dose must be replenished after each dialysis because the artificial kidney completely eliminates the drug during treatment. 4 This approach ensures full therapeutic retention and facilitates directly observed therapy. 1
Critical Implementation Points
Do Not Reduce the Milligram Dose:
Concentration-dependent antibiotics like fosfomycin require adequate peak levels for efficacy, regardless of renal function. 1 Smaller doses may compromise bactericidal activity, so the standard 2-gram dose is maintained even in complete renal failure. 1, 2
Post-Dialysis Administration is Mandatory:
Administering fosfomycin before or during dialysis results in 70-80% drug loss through the dialyzer membrane. 3, 2 Post-dialysis dosing prevents this premature removal and ensures the full therapeutic dose circulates between sessions. 1, 2, 4
Residual Renal Function is Irrelevant:
For patients newly initiated on hemodialysis with some residual kidney function, the post-dialysis dosing regimen remains appropriate regardless of residual function. 1 The thrice-weekly schedule after each dialysis session is the standard approach. 1
Monitoring Considerations
Consider serum drug concentration monitoring in patients with severe infections or those not responding to therapy, as levels can vary based on residual renal function and dialysis efficiency. 1 However, routine monitoring is not required for most patients, as the post-dialysis dosing strategy reliably maintains therapeutic levels. 2
Common Pitfalls to Avoid
- Never administer before dialysis: This results in 70-80% drug loss and therapeutic failure 3, 2
- Never reduce the 2-gram dose: Renal impairment is not an indication to lower the milligram amount 1, 2
- Never skip post-dialysis doses: Each dialysis session removes the drug, requiring replacement 4
- Never use daily dosing: Patients on thrice-weekly hemodialysis receive three doses per week, not seven 1
Loading Dose Considerations
If a loading dose is clinically indicated for severe infections, administer the full standard dose without reduction, as loading doses are not affected by renal impairment. 1 The subsequent maintenance regimen follows the standard 2 grams post-dialysis schedule. 1