Dosing Recommendations for IV Cefazolin and Azithromycin in ESRD on Hemodialysis
For this patient with ESRD on hemodialysis three times weekly, administer cefazolin 2 grams IV after each dialysis session (three times per week), and azithromycin at standard dosing of 500 mg IV daily without any dose adjustment.
Cefazolin Dosing in ESRD
Cefazolin requires significant dose adjustment in ESRD because approximately 60-80% is renally excreted unchanged, with a prolonged half-life of approximately 9-10 hours in dialysis patients compared to 1.8 hours in normal renal function 1, 2.
Recommended Regimen:
- Loading dose: 2 grams IV after dialysis session
- Maintenance dose: 2 grams IV after each dialysis session (three times weekly)
- Timing: Always administer post-dialysis, as hemodialysis removes approximately 60% of cefazolin 2
Rationale:
- Cefazolin achieves peak serum concentrations of approximately 100 mcg/mL after a 2-gram dose in dialysis patients, with trough levels of 12 mcg/mL before the next dialysis session 3
- The interdialytic half-life extends to 9.35 hours, allowing for three-times-weekly dosing that maintains therapeutic levels between sessions 3
- Post-dialysis administration prevents premature drug removal and facilitates directly observed therapy 4
Critical Pitfall:
Do not reduce the individual dose amount—instead, extend the dosing interval. Reducing dose size lowers peak concentrations and compromises efficacy 4. The three-times-weekly schedule maintains adequate drug exposure while preventing accumulation 2.
Azithromycin Dosing in ESRD
Azithromycin requires NO dose adjustment in ESRD, including patients on hemodialysis or peritoneal dialysis 5.
Recommended Regimen:
- Standard dose: 500 mg IV daily
- No adjustment needed for renal function
- No supplemental dosing required post-dialysis
Rationale:
- Unlike clarithromycin (which requires 50% dose reduction when creatinine clearance is <30 mL/min), azithromycin maintains standard dosing in end-stage renal disease 5
- Azithromycin undergoes primarily hepatobiliary elimination rather than renal excretion 5
- The Infectious Diseases Society of America specifically notes that clarithromycin dosing adjustments should not be extrapolated to azithromycin 5
Key Distinction:
This is a critical difference between macrolides—clarithromycin requires dose reduction to 250 mg daily in ESRD, but azithromycin does not 4, 5. Do not confuse these two agents when prescribing for dialysis patients.
Practical Implementation
Dialysis Day Schedule:
- Administer cefazolin 2 grams IV immediately after dialysis session
- Administer azithromycin 500 mg IV at standard time (can be given with or separate from cefazolin)
Non-Dialysis Days:
- Cefazolin: None (three times weekly only)
- Azithromycin: 500 mg IV daily
Monitoring Considerations:
- While therapeutic drug monitoring is not routinely required for cefazolin at this regimen, consider measuring serum concentrations if clinical response is inadequate or toxicity is suspected 4
- Monitor for signs of antibiotic-associated complications, particularly given the recurrent pneumonia and prior antibiotic failures
- Watch for QT prolongation with azithromycin, especially if the patient is on other QT-prolonging medications common in dialysis patients