Gas Antisolvent Micronization of Pharmaceutical Powders (Spine title: Gas Antisolvent Micronization of Pharmaceutical Powders) (Thesis format: Monograph) by Shawn Dodds Graduate Program in Engineering Department of Chemical and Biochemical Engineering A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering Science Faculty of Graduate Studies The University of Western Ontario London, Ontario, Canada © Shawn Dodds, 2006 THE UNIVERSITY OF WESTERN ONTARIO FACULTY OF GRADUATE STUDIES Certificate of Examination Supervisor Examiners ______________________________ ______________________________ Dr. Paul Charpentier Dr. Amin Rizkalla ______________________________ Supervisory Committee Dr. Kibret Mequanint ______________________________ ______________________________ Dr. Sohrab Rohani Dr. Lars Konermann The thesis by Shawn Dodds entitled: Gas Antisolvent Micronization of Pharmaceutical Powders is accepted in partial fulfilment of the requirements for the degree of Master of Engineering Science Date August 10th, 2006 _______________________________ Chair of the Thesis Examination Board - ii - Abstract The purpose of this work was to study the effect of process conditions on the crystallization of beclomethasone-17,21-dipropionate (BDP), an anti-inflammatory steroid commonly used to treat asthma, using the gas antisolvent (GAS) technique. A better understanding of how GAS process conditions affect the particle size distribution (PSD) of BDP through experimental and modelling work is desirable to optimize GAS operating conditions for the production of inhalable powders. The GAS technique was chosen for its ability to produce micron sized particles, while reducing the residual organic solvent content to the ppm level. The effects of temperature, agitation rate, and antisolvent addition rate on the PSD were studied. An increase in the agitation rate led to a decrease in particle size at 20oC, but affected only the level of aggregation at 25oC. Therefore, it was concluded that at 20oC mass transfer was limiting, while at 25oC it was not. It was also found that an increase in the CO2 addition rate led to a decrease in the size of both aggregates and particles. However, the particle sizes were identical at both 20 and 25oC, though the aggregate sizes were lower at 20oC. Therefore an increase in flowrate acts by decreasing the precipitation time scale, but has little effect on mass transfer. A phase equilibrium study was performed using two different models: an expanded liquid phase model (ELPM), and a relative partial molar volume fraction (RPMVF) model. While both models were satisfactory for model compounds such as naphthalene, only the RPMVF model could describe the more complicated cholesterol- acetone-CO2 system. - iii - A population balance was used to model the PSDs of GAS processed powders. Secondary nucleation was implemented to account for the bimodal nature of the PSD. While a good representation of the primary mode was achieved, secondary nucleation could not account for the second mode. Therefore, an effect other than secondary nucleation, such as agglomeration, was responsible for producing the bimodal PSDs observed experimentally in the BDP/acetone/CO2 system. However, the model still achieved a good fit of the dp(50%) and dp(90%) experimental results, and so is useful for approximating particle sizes, and could be used to estimate the inhalable fraction of a powder. Keywords: Beclomethasone-17,21-dipropionate, gas antisolvent process, supercritical fluids, phase modelling, population balance - iv - Acknowledgements No project is ever the work of an individual, and as such there are many people to thank. First of all, I would like to thank my advisor, Dr. Paul Charpentier, for his support and friendship throughout this project. Dr. Jolyon Mitchell’s expertise in particle sizing and the pharmaceutical industry in general was invaluable, and this project certainly would have stalled very early without his help. Also, I would like to thank Mr. Jeff Wood for providing a critical eye when things were going well, and excellent ideas when they were not. The help of Todd Simpson and Mohamad Rahbari running the SEM was greatly appreciated, as was the help of Tim Stephens with the Mastersizer and Touraj Manifar with the HPLC. Also, Mehdi Sheikhzadeh, Mike Gaylard and Souheil Afara provided technical assistance on numerous occasions. I would like to thank all of my colleagues in the Laboratory for Environmentally Friendly Solvents, my friends and my family for their support. Finally, I would like to thank Kathy for her constant moral support, and for not getting angry after a few too many late nights in the lab. - v - Table of Contents Certificate of Examination............................................................................................... ii Abstract............................................................................................................................. iii Acknowledgements ............................................................................................................v Table of Contents ............................................................................................................. vi List of Figures................................................................................................................. viii List of Tables .................................................................................................................... xi Nomenclature .................................................................................................................. xii List of Symbols for Sections 5 and 6 ............................................................................ xiii 1. Introduction................................................................................................................1 2. Background and Literature Review.........................................................................4 2.1. Supercritical and near-critical fluids................................................................... 4 2.2. GAS process........................................................................................................ 9 2.3. Crystallization................................................................................................... 11 2.4. Asthma .............................................................................................................. 13 2.5. Beclomethasone dipropionate........................................................................... 16 2.6. Literature Review: pharmaceutical micronization by supercritical fluids........ 20 2.6.1. Generic Pharmaceuticals.......................................................................... 21 2.6.2. Proteins..................................................................................................... 25 2.6.3. Steroids & Hormones................................................................................ 28 2.6.4. Encapsulation ........................................................................................... 32 3. Experimental Procedures........................................................................................36 3.1. GAS experiments.............................................................................................. 36 3.1.1. Materials................................................................................................... 36 3.1.2. Apparatus.................................................................................................. 36 3.1.3. GAS crystallization procedure.................................................................. 39 3.2. Controller tuning............................................................................................... 40 3.2.1. Apparatus.................................................................................................. 40 3.2.2. Procedure.................................................................................................. 41 3.3. Particle characterization.................................................................................... 42 3.3.1. Laser diffraction particle sizing................................................................ 42 3.3.2. Scanning Electron Microscopy (SEM)...................................................... 43 3.3.3. Differential Scanning Calorimetry (DSC) ................................................ 44 3.3.4. High Performance Liquid Chromatography (HPLC)............................... 45 4. Experimental Results...............................................................................................46 4.1. PID controller tuning ........................................................................................ 46 4.2. GAS experiments.............................................................................................. 52 4.2.1. Effect of agitation rate .............................................................................. 58 4.2.2. Effect of CO2 Addition Rate ...................................................................... 66 4.2.3. Effect of Temperature ............................................................................... 73 5. Thermodynamics of the GAS process....................................................................76 5.1. Expanded liquid phase model (ELPM)............................................................. 76 5.2. Relative partial molar volume fraction (RPMVF) model................................