Unit Conversion for Colistin: MU vs IU
No, 0.75 MU (Million Units) is NOT the same as 75,000 IU (International Units)—0.75 MU equals 750,000 IU, which is 10 times higher than 75,000 IU. This is a critical distinction that could lead to severe underdosing if confused.
Understanding Colistin Unit Conversions
The correct conversion is: 1 MU = 1,000 IU 1, 2, 3
Therefore:
- 0.75 MU = 750,000 IU (not 75,000 IU)
- 75,000 IU = 0.075 MU (which is 10-fold lower)
Critical Context for Pediatric Dosing with Renal Impairment
Loading Dose (Always Full Dose Regardless of Renal Function)
Always administer the full loading dose of 0.15 MU/kg (equivalent to 5 mg CBA/kg) regardless of renal function to rapidly achieve therapeutic levels 2, 4. This is non-negotiable—never reduce the loading dose in renal impairment 2.
Maintenance Dose Adjustments Based on Renal Function
For pediatric patients, maintenance dosing must be adjusted based on creatinine clearance 2:
- Normal renal function: 0.075 MU/kg every 12 hours (equivalent to 2.5-5 mg CBA/kg/day) 1, 2
- Moderate renal impairment (CrCl 30-49 mL/min): 2.5 mg CBA/kg once daily 2
- Severe renal impairment (CrCl 10-29 mL/min): 1.5 mg CBA/kg every 36 hours 2
Critical Pitfalls to Avoid
Do not underdose colistin in an attempt to reduce nephrotoxicity—subtherapeutic levels lead to treatment failure and increased mortality while still carrying nephrotoxic risk 2, 4. The confusion between MU and IU could result in a 10-fold underdosing error, which would be catastrophic for patient outcomes.
Monitor renal function 2-3 times per week during therapy 2, 4, as acute kidney injury occurs in approximately 20% of pediatric patients with normal baseline renal function 5, though nephrotoxicity risk in pediatric populations (5.8%) is lower than in adults (36%) 2, 4.
Never use colistin as monotherapy—always combine with at least one additional agent to which the pathogen displays in vitro susceptibility 1, 2, 3.