What is the recommended dose of nebulized colistin (polymyxin E) for treatment?

Nebulized Colistin Dosing

For nebulized colistin in ventilator-associated pneumonia or tracheobronchitis, administer 2 million IU every 8-12 hours, with higher doses (up to 4 million IU three times daily) reserved for non-resolving cases. 1

Standard Dosing Regimen

• The recommended dose is 2 million IU every 8 or 12 hours delivered via ultrasonic or vibrating plate nebulizers 1
• This dosing achieves lung tissue concentrations >5 times the minimum inhibitory concentration (MIC) in regions with multiple foci of bronchopneumonia 2
• The evidence supporting this recommendation is graded as BIII (moderate recommendation, low-quality evidence) 1

Higher Dose Considerations

• For non-resolving pneumonia cases, escalate to 4 million IU three times per 24 hours (total 12 million IU/day) 3
• This higher dosing regimen has demonstrated clinical cure rates of 67.1% in prospective randomized trials 3
• Higher doses provide therapeutic concentrations even in regions with confluent pneumonia where standard doses may be subtherapeutic 2

Critical Administration Requirements

Nebulized colistin must always be combined with intravenous antimicrobial therapy for pneumonia 1. This is a strong recommendation because:

• Nebulization alone may not achieve adequate systemic concentrations 2
• The combination approach addresses both local lung infection and potential bacteremia 1

For tracheobronchitis specifically, nebulized antibiotics are recommended, though the necessity of concurrent IV therapy remains uncertain and requires further study 1

Device Selection

• Use ultrasonic or vibrating plate nebulizers exclusively 1
• These devices optimize drug delivery to the lower respiratory tract compared to jet nebulizers 1

Clinical Advantages Over IV Route

When comparing nebulized versus intravenous colistin, the aerosolized route demonstrates:

• Significantly lower nephrotoxicity (17.8% vs 39.4% acute renal failure) 3
• Faster bacterial eradication (mean 9.89 vs 11.26 days) 3
• Earlier ventilator weaning (mean gain of 5 ventilator-free days in ICU survivors) 3
• Better oxygenation improvement (P/F ratio 349 vs 316 at day 14) 3

Important Caveats

• Do not use nebulized antibiotics for colonization alone—this is contraindicated (DIII recommendation) 1
• Select between colistin and aminoglycosides based on susceptibility testing; no definitive preference exists when both are susceptible 1
• For isolates with MICs close to susceptibility breakpoints, nebulized therapy is particularly indicated 1
• Nebulized colistin is preferred over polymyxin B for inhaled administration based on controlled clinical evidence 4

Dosing Units Clarification

• Colistin is administered as colistimethate sodium (CMS), the inactive prodrug 5
• 1 million IU colistin = 80 mg CMS 5
• The nebulized doses (2-4 million IU) are substantially lower than IV loading doses (9 million IU) because direct lung delivery bypasses systemic distribution 5, 3