Recommended Loading Dose of Colistin for a 69kg Man
For a 69kg man, the recommended loading dose of colistin (colistimethate) is 10.5 million international units (MIU). 1, 2
Calculation Method
The loading dose is calculated using the following approach:
- The recommended loading dose is 5 mg of colistin base activity (CBA) per kg of body weight 1, 2
- For a 69kg man: 5 mg/kg × 69kg = 345 mg CBA
- Conversion factor: 1 MIU of colistimethate sodium ≈ 33 mg of colistin base activity 2
- Therefore: 345 mg CBA ÷ 33 mg/MIU = 10.45 MIU (rounded to 10.5 MIU)
Dosing Considerations
- The loading dose should be administered intravenously over 0.5-1 hour 2
- This loading dose is critical regardless of renal function to rapidly achieve therapeutic concentrations 2
- After the loading dose, maintenance dosing should be calculated based on renal function using the formula: 2.5 mg CBA × (1.5 × CrCl + 30) IV every 12 hours 1, 2
Important Clinical Considerations
- Colistin has a narrow therapeutic window, making appropriate dosing crucial 2
- Underdosing may lead to treatment failure and development of resistance 3
- Higher colistin doses have been associated with improved microbiological success (adjusted odds ratio per 1 mg/kg/day = 1.74) 3
- However, higher doses also increase the risk of nephrotoxicity (8-30% of patients) 2, 3
- Close monitoring of renal function during treatment is essential 2
Common Pitfalls to Avoid
- Failing to administer a loading dose, which can delay achieving therapeutic concentrations
- Confusion between colistin base activity (CBA) and colistimethate sodium (CMS) dosing
- Using body weight-based dosing for maintenance therapy rather than the recommended renal function-based approach
- Inadequate monitoring of renal function during treatment
Alternative Considerations
If the patient has severe renal impairment or is on renal replacement therapy, dosing should be adjusted accordingly. For patients on hemodialysis or continuous renal replacement therapy, specific dosing regimens are recommended 4, 5.
For critically ill patients with multidrug-resistant infections, consider that newer agents such as ceftolozane-tazobactam, ceftazidime-avibactam, or imipenem-cilastatin-relebactam may be preferred over colistin if the organism is susceptible, due to better safety profiles 2.