Micronization of insulin from halogenated alcohol solution using supercritical carbon dioxide as antisolvent

The objective of this research was to obtain particles of insulin in a size range suitable for pulmonary inhalation therapy, without seriously degrading the insulin or reducing the potency of the insulin, by precipitating insulin from solution in halogenated alcohol using supercritical carbon dioxide (CO₂) as an antisolvent. Pulmonary delivery of insulin via inhalation of dry powders or liquid aerosols is a promising alternative form of diabetes therapy. Particle micronization via precipitation from organic solvents using supercritical CO₂ as an antisolvent has been shown to produce particles of various pharmaceutical compounds with size distributions suitable for pulmonary inhalation therapy (narrowly distributed, with mass mean aerodynamic diameters in the range of 1–5 μm). Halogenated alcohols make excellent solvents for proteins, such as insulin.; Biosynthetic human insulin crystals (mass mean aerodynamic diameter = 22 μm, standard deviation = 1.7 μm) were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the solution was sprayed through an ultrasonic nozzle into supercritical CO₂, and the insulin precipitated as the HFIP and CO₂ became miscible. The experimental design consisted of a 23 factorial with a center point replicate. Experimental parameters investigated included pressure (83.7 and 97.5 bar), solution concentration (15 and 30 mg/mL) and solution flow rate (2 and 4 mL/min). Temperature (37°C), CO₂ mass flow rate (137 g/min) and volume of solution sprayed (20 mL) were held constant. High-performance liquid chromatography, circular dichroism spectroscopy, infrared and Raman spectroscopy, scanning electron microscopy, size distribution analysis, thermogravimetric analysis, and atomic absorption spectroscopy were used to characterize the processed insulin powder at Lilly Research Laboratories.; The processed insulin retained its potency, was slightly degraded chemically, and experienced reversible structural changes. Particles in the range of 1–5 μm could be obtained through deagglomeration of the precipitated powder, which consisted of physical aggregates of 50 nm spheres. Over the ranges of operating variables studied, the factors chosen for the experimental design had little effect on the product characteristics. Supercritical fluid processing of insulin from solution in HFIP, followed by deagglomeration, is a viable means of producing microparticles suitable for pulmonary inhalation therapy.