What is the recommended dose of inhaled colistin for a patient with bronchiectasis and chronic Pseudomonas aeruginosa infection, who is taking sotalol for arrhythmia management and has impaired renal function?

Inhaled Colistin Dosing for Bronchiectasis with Chronic Pseudomonas aeruginosa Infection

The recommended dose of inhaled colistin is 1 million international units (1 MU) twice daily, administered via nebulizer. 1, 2, 3

Standard Dosing Regimen

• Administer 1 million IU (1 MU) of colistin twice daily via nebulizer 1, 2, 3
• The British Thoracic Society specifically endorses this as first-line therapy for patients with bronchiectasis and chronic P. aeruginosa infection experiencing ≥3 exacerbations per year 1, 2
• Treatment duration should be at least 6 months to achieve clinical benefit 3, 4

Critical Safety Contraindications in This Patient

This patient has impaired renal function, which creates a significant safety concern:

• Avoid inhaled aminoglycosides (including colistin) if creatinine clearance is <30 mL/min 1, 2
• Use with extreme caution if creatinine clearance is between 30-50 mL/min, with close monitoring 1
• The patient is also taking sotalol, which can prolong QT interval—while colistin itself has minimal systemic absorption when inhaled, monitor for any additive nephrotoxic effects 1

Preparation and Administration Details

• Prepare isotonic solution by dissolving 2 million units of colistin in 3 mL water plus 3 mL physiological saline (for a single dose, use 1 million units in 3 mL total isotonic solution) 1
• Use a nebulizer that produces particles in the 2-5 μm range to ensure adequate lower airway deposition 1
• Perform a bronchodilator challenge test when stable before initiating therapy to assess for bronchospasm 1
• Administer bronchodilators before colistin if the patient has reactive airways 1

Alternative Options Given Renal Impairment

If creatinine clearance is <30 mL/min, consider these alternatives instead:

• Azithromycin 250 mg three times weekly as an alternative to inhaled antibiotics 1
• Erythromycin can also be used as an alternative oral macrolide option 1
• These macrolides are recommended specifically for patients who cannot tolerate inhaled antibiotics 1, 2

Monitoring Requirements

• Review patients every 6 months to assess efficacy, toxicity, and continuing need 1, 2, 5
• Monitor sputum culture and sensitivity regularly, though in vitro resistance may not affect clinical efficacy 1, 5
• Assess for ototoxicity and balance issues, using with caution if significant hearing loss or balance problems exist 1, 2
• Avoid concomitant nephrotoxic medications (this is particularly important given the patient's sotalol use and renal impairment) 1, 2

Clinical Efficacy Evidence

• Inhaled colistin extends median time to exacerbation from 111 to 165 days in intention-to-treat analysis, with greater benefit (168 vs 103 days, p=0.038) in adherent patients 3
• Reduces P. aeruginosa bacterial density significantly at 4 weeks (p=0.001) and 12 weeks (p=0.008) 3
• Improves quality of life as measured by St. George's Respiratory Questionnaire at 26 weeks (p=0.006) 3
• Achieves P. aeruginosa eradication in approximately 45% of treated patients 6, 4

Common Pitfalls to Avoid

• Do not use inhaled colistin if creatinine clearance is <30 mL/min—this is an absolute contraindication per British Thoracic Society guidelines 1, 2
• Discontinuation rates due to adverse effects can reach 25% in elderly patients, most commonly due to bronchospasm or cough 6
• Nephrotoxicity occurs in approximately 8.3% of patients receiving systemic colistin, with risk factors including pre-existing renal insufficiency and diabetes 7
• Ensure respiratory specialist initiation of prophylactic antibiotics 1, 2