Colistin Dosing in Maintenance Hemodialysis Patients
For patients on maintenance hemodialysis, administer colistin methanesulfonate (CMS) 2 million IU every 12 hours with a normal loading dose of 6-9 million IU, and schedule dialysis at the end of a dosing interval with a supplemental 1.5 million IU dose after each dialysis session.
Loading Dose
The loading dose remains critical even in hemodialysis patients and should not be reduced 1. Administer 6-9 million IU of CMS regardless of renal function, as the loading dose ensures adequate plasma concentrations from day one 1. The pharmacokinetic rationale is that colistin has a relatively long half-life, and without a loading dose, it takes 2-3 days to reach therapeutic steady-state concentrations—a delay that can be fatal in critically ill patients 1.
Maintenance Dosing
The maintenance dose is 2 million IU CMS every 12 hours 1. This represents a substantial reduction from the standard dose in patients with normal renal function (4.5 million IU every 12 hours), reflecting the dramatically reduced clearance in hemodialysis patients.
Timing with Dialysis Sessions
Critical timing consideration: Schedule hemodialysis at the end of a dosing interval 1. This is essential because approximately 30% of the administered CMS dose is removed during a single dialysis session 2.
After each dialysis session, administer a supplemental dose of 1.5 million IU 3. This replaces the drug removed during dialysis and maintains therapeutic concentrations. Research demonstrates that dialysis clearance of CMS is approximately 4.26-5.67 L/h, representing substantial drug removal 3, 2.
Practical Dosing Schedule Example
- Day 1: Loading dose of 6-9 million IU
- Non-dialysis days: 2 million IU every 12 hours (total 4 million IU/day)
- Dialysis days: 2 million IU every 12 hours PLUS 1.5 million IU post-dialysis (total 5.5 million IU/day) 3
Important Monitoring Considerations
Renal function monitoring remains mandatory even in dialysis patients 4. While these patients already have end-stage renal disease, colistin nephrotoxicity can still impact residual renal function and complicate future transplant eligibility. Monitor for:
- Changes in residual urine output
- Electrolyte disturbances
- Signs of additional nephrotoxic injury
Dosing Unit Conversion Warning
Critical safety note: Colistin dosing uses multiple unit systems that frequently cause prescribing errors 1, 5. The conversion is:
- 1 million IU = 80 mg CMS (mass) = 33 mg colistin base activity (CBA)
Always verify which unit system your institution uses to prevent potentially fatal dosing errors.
Combination Therapy Consideration
While the evidence for combination therapy versus monotherapy remains controversial 4, combination therapy with a carbapenem or other active agent is preferred when treating serious infections 5. The 2023 guidelines provide moderate-quality evidence supporting combination therapy over monotherapy for improved treatment failure rates and microbiological clearance 5.
Alternative: Polymyxin B
Consider polymyxin B as an alternative, which may have lower nephrotoxicity and does not require dose adjustment in dialysis patients (1.5-3 mg/kg/day with 2-2.5 mg/kg loading dose) 1. Polymyxin B is not a prodrug and is not significantly removed by dialysis, simplifying dosing in this population.