Colistin Dosing for Hemodialysis Patients
For adult patients on intermittent hemodialysis, administer a normal loading dose of 6-9 million IU colistimethate sodium (CMS), followed by a maintenance dose of 2 million IU every 12 hours, with dialysis performed toward the end of the dosing interval 1.
Dose Calculation Using Your Formulation
Given your vial contains:
- 150 mg colistimethate sodium = 4.5 million IU (MIU) colistin base activity
- 1 mg CMS = 30,000 units
Loading Dose
- Target: 6-9 million IU
- Using your vials: 1.5 to 2 vials (6.75-9 MIU)
- In mg: 200-300 mg CMS
The loading dose is critical and should be given regardless of renal function, as plasma colistin concentrations remain suboptimal for 2-3 days without it 1.
Maintenance Dose
- Target: 2 million IU every 12 hours
- Using your vials: Approximately 0.44 vials per dose (67 mg CMS)
- Practical dosing: Reconstitute one 150 mg vial and administer 0.9 mL of the reconstituted solution (at 75 mg/mL concentration per FDA label) to deliver approximately 67 mg
Critical Timing Considerations
Schedule hemodialysis at the end of the CMS dosing interval 1. This is essential because:
- CMS is extensively removed by dialysis (approximately 30% of the administered dose) 2
- Dialysis clearance of CMS is substantial at 4.26-5.67 L/h 2
- A supplemental dose should be administered after the dialysis session 3, 2
Research data suggests that on dialysis days, patients may benefit from a supplemental dose of 1.5 MIU (approximately 50 mg CMS or 0.33 vials) immediately post-dialysis 3.
Pharmacokinetic Rationale
The evidence strongly supports this approach because:
- Colistin exposure is increased 3-fold in hemodialysis patients compared to those with normal renal function, as a greater fraction of CMS converts to colistin 3
- CMS nonrenal clearance is actually increased in ICU-HD patients, but colistin accumulates due to enhanced conversion 3
- The half-life of colistin is relatively long compared to the dosing interval, necessitating the loading dose 1
Monitoring and Safety
Monitor renal function closely during treatment 4. While dialysis patients already have renal impairment, colistin nephrotoxicity remains a concern and is associated with higher mortality 1. The incidence of renal failure appears lower with polymyxin B than colistin 1, which may be considered as an alternative if available.
Common Pitfalls to Avoid
Do not skip the loading dose - This is the most critical error. Even with renal dysfunction, the loading dose must be given to achieve therapeutic levels quickly 1
Do not dialyze immediately after dosing - This removes the drug before it can exert antibacterial effect 1, 3, 2
Do not use the same maintenance dose as patients with normal renal function - The 4.5 million IU every 12 hours recommended for creatinine clearance >50 mL/min is excessive for dialysis patients 1, 4
Avoid confusion between dosing units - Multiple reporting systems exist (IU, mg CMS, mg colistin base activity), which frequently causes errors 1. Always verify conversions: 1 million IU ≈ 80 mg CMS ≈ 30 mg colistin base activity 1
Alternative Consideration
If colistin toxicity is a major concern, polymyxin B may be preferable with a loading dose of 2-2.5 mg/kg followed by 1.5-3 mg/kg/day in 2 doses, with no dose adjustment needed for dialysis 1.