Colistin powders with high aerosolisation efficiency for respiratory infection: preparation and in vitro evaluation

Area of Science:

• Pharmaceutical Technology
• Microbiology
• Drug Delivery

Background:

• Colistin is a last-line antibiotic for multi-drug-resistant Gram-negative bacterial respiratory infections.
• Parenteral colistin administration is limited by nephrotoxicity.
• Inhalation therapy offers a promising alternative to improve efficacy and reduce adverse effects.

Purpose of the Study:

• To develop inhalable powder formulations of colistin (sulphate) using spray drying.
• To evaluate the physical stability, aerosol performance, and antimicrobial activity of the spray-dried colistin formulations.

Main Methods:

• Spray drying was used to produce inhalable colistin (sulphate) powder formulations.
• Antimicrobial activity was assessed against Acinetobacter baumannii using broth micro-dilution.
• Physical stability was evaluated at various relative humidity (RH) and temperature conditions.
• Aerosol efficiency was measured by emitted dose and fine particle fraction.

Main Results:

• Spray-dried colistin powders retained antimicrobial activity.
• Formulations were amorphous and stable at 60% RH and 25°C, with high aerosol efficiency (>86% emitted dose, >83% fine particle fraction).
• Elevated RH (≥75%) decreased aerosol performance and caused particle fusion at 90% RH without re-crystallisation.

Conclusions:

• Spray drying is a suitable method for producing physically stable, inhalable colistin powder formulations.
• The developed formulations maintain antimicrobial activity and good aerosol properties under ambient conditions.
• This approach holds potential for effective and safer treatment of respiratory infections.