Colistin Dosing in Dialysis Patients
The proposed regimen of 2 million IU twice daily plus 1 million IU post-dialysis supplementation is NOT supported by current evidence and should not be used. Instead, follow evidence-based dosing algorithms that account for renal function and dialysis modality.
Recommended Approach
For Patients on Intermittent Hemodialysis (Non-Dialysis Days)
Use standard dosing based on creatinine clearance 1, 2:
- Loading dose: 9 MU (million units) of colistimethate sodium initially
- Maintenance: 4.5 MU twice daily (every 12 hours) for patients with normal renal function
- For renal impairment, adjust according to creatinine clearance:
- CrCl 50-79 mL/min: 2.5-3.8 mg/kg divided into 2 doses daily
- CrCl 30-49 mL/min: 2.5 mg/kg once or twice daily
- CrCl 10-29 mL/min: 1.5 mg/kg every 36 hours
For Patients on Continuous Renal Replacement Therapy (CRRT)
Higher doses are required 3, 4:
- Loading dose: 9 MU initially (essential for rapid therapeutic levels)
- Maintenance: 4.5 MU every 12 hours (total 9 MU daily)
- Some evidence suggests even higher dosing (6.75 MU every 12 hours) may be needed 4
- Supplemental dosing after dialysis sessions: An additional dose equivalent to what was removed may be warranted 2, 5
Critical Considerations
Why Your Proposed Regimen is Problematic
The "2 million morning and night plus 1 million supplement" approach (total 5 million IU daily) is:
- Significantly underdosed compared to guideline recommendations of 9 MU daily for critically ill patients 3
- Lacks a loading dose, which delays achievement of therapeutic concentrations by 2-3 days 6
- Not based on pharmacokinetic principles that account for the slow conversion of colistimethate to active colistin
Dialysis-Specific Factors
Colistin is substantially removed by dialysis 2, 5:
- In SLEDD (sustained low-efficiency daily dialysis), extracorporeal clearance accounts for up to 67% of total drug clearance 5
- CRRT significantly increases colistin clearance, necessitating supplemental dosing 4, 7
- The timing and modality of dialysis critically affect drug levels
Target Attainment Issues
Pharmacodynamic targets are frequently missed with standard dosing 2, 4:
- Target: fAUC/MIC ≥12 for bacterial killing
- In patients with CrCl ≥80 mL/min, even maximum doses (360 mg colistin base activity daily) achieve target in <40% of patients 2
- For pathogens with MIC ≥1 mg/L, monotherapy often fails regardless of dose 2, 7
Practical Dosing Algorithm
Step 1: Determine Dialysis Status
- Intermittent HD: Dose on non-dialysis days based on residual renal function
- CRRT/CVVHDF: Use high-dose regimen with continuous monitoring
Step 2: Calculate Loading Dose
Step 3: Maintenance Dosing
- CRRT patients: 4.5 MU every 12 hours (minimum) 3, 4
- Intermittent HD: Adjust based on CrCl on non-dialysis days 1, 2
- Post-dialysis supplement: Consider additional 2-3 MU after each HD session 2, 5
Step 4: Monitor and Adjust
- Renal function: Check daily; acute kidney injury occurs in 30-60% of patients 3
- Therapeutic drug monitoring: Target Css,avg of 2 mg/L (if available) 2, 6
- Clinical response: Assess at 48-72 hours
Critical Pitfalls to Avoid
Omitting the loading dose is the most common error—colistimethate converts slowly to active colistin, and without a loading dose, therapeutic levels are delayed by days 6.
Underdosing in CRRT patients leads to treatment failure—dialysis removes substantial amounts of drug, requiring higher maintenance doses than in non-dialysis patients 4, 5.
Ignoring MIC values when the pathogen has MIC ≥1 mg/L—consider combination therapy with carbapenems or other agents rather than colistin monotherapy 3.
Failing to monitor renal function closely—nephrotoxicity is dose-related and occurs frequently, but is often reversible if detected early 3, 8.
When to Consider Alternatives
If the pathogen MIC is ≥2 mg/L, colistin monotherapy is unlikely to succeed even with optimal dosing 2, 7. Consider: