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Nebulisers for the Generation of Liposomal Aerosols

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Nebulisers for the Generation of Liposomal Aerosols NEBULISERS FOR THE GENERATION OF LIPOSOMAL AEROSOLS Paul Anthony Bridges BPharm MRPharmS School of Pharmacy University of London London June 1997 Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy ProQuest Number: 10104800 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10104800 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 ABSTRACT The thesis details investigations into the use of various types of medical nebuliser for the generation of liposomal aerosols. Chapter 1 provides a comprehensive introduction to the theory and practice of drug delivery to the respiratory tract. It also reviews the potential applications of inhaled liposomes to drug delivery, and the devices used to generate liposomal aerosols. A preliminary investigation into the physicochemical attributes of liposomes which may. influence aerosol generation is detailed in chapter 2. These include studies of the stability of liposome bilayers to disruptive energy (ie. membrane extrusion and sonication), investigations of the surface tension and viscosity of liposomes, and also the release of a liposomally entrapped hydrophilic marker. Chapter 3 demonstrates how these physicochemical attributes may influence nebulised liposomal aerosols. Most notably, the aerosol droplet size and output rate are proportional to the concentration of the formulation. The residual liposome concentration is determined by the mean liposome size. The droplet size, nébulisation time, aerosol output, and residual liposome concentration are all significantly influenced by the particular jet nebuliser model selected for aerosol generation. The relative stability of different liposome formulations to nébulisation is also determined by a variety of factors, as revealed in chapter 4 of the thesis. The release of an entrapped marker, and the reduction in liposome size during nébulisation, is influenced by the nebuliser model, and also the liposome size and bilayer composition. Chapter 5 investigates the freeze drying of liposomes. The chapter concludes that liposomes for nébulisation may be freeze dried in the presence of a cryoprotectant, without influencing the aerosol produced following subsequent rehydration. Chapter 6 reveals that the droplet size produced from ultrasonic nebulised liposomes is relatively large, and the output inefficient from concentrated formulations. In addition, ultrasonic nébulisation is associated with similar liposome stability concerns as jet nébulisation. TABLE OF CONTENTS Title page .................................................................................................................................1 Abstract ................................................................................................................................... 2 Table of contents .....................................................................................................................3 List of tables ............................................................................................................................7 List of figures.......................................................................................................................... 9 Abbreviations .......................................................................................................................16 Acknowledgements ...............................................................................................................18 1 INTRODUCTION 1.1 The inhaled route for drugs ....................................................................................19 1.2 The respiratory tract ...............................................................................................20 1.3 Inhaled aerosols ....................................................................................................... 23 1.4 Fate of inhaled matter .............................................................................................23 1.4.1 Deposition of particles .................................................................................23 1.4.2 Clearance of deposited particles .................................................................. 26 1.5 Delivery of drugs to the lung ..................................................................................27 1.5.1 Inhaled drugs for local action ..................................................................... 27 1.5.2 Inhaled drugs for systemic activity .............................................................27 1.5.3 Fate of inhaled drugs ....................................................................................28 1.5.4 Characteristics of therapeutic aerosols ........................................................30 1.6 Therapeutic aerosol generators .............................................................................. 32 1.6.1 Metered dose inhalers ....................................................................................32 1.6.2 Dry powder inhalers ......................................................................................34 1.6.3 Nebulisers .....................................................................................................35 1.6.3.1 Ultrasonic nebulisers .................................................................... 36 1.6.3.2 Jet nebulisers .................................................................................37 1.6.3.3 Output of nebulisers ..................................................................... 38 1.6.3.4 Nébulisation times ........................................................................40 1.6.3.5 Temperature and concentration effects ........................................40 1.6.3.6 Droplet size ...................................................................................41 1.6.3.7 Nebulisers and liposomes ............................................................43 1.7 Liposomes .............................................................................................................. 43 1.7.1 Liposomes as drug carriers .........................................................................44 1.7.2 Medical applications of liposomes ...........................................................46 1.7.3 Disadvantages of liposomes as drug carriers .............................................48 1.8 The pulmonary delivery of liposomes ................................................................ 48 1.9 Liposomes as drug carriers to the respiratory tract ......................................... 52 1.10 Human studies of inhaled liposomes .................................................................. 64 1.11 Devices used for the aerosolisation of liposomes ................................................ 68 1.12 Aims of the study ....................................................................................................71 2 PHYSICOCHEMICAL PROPERTIES OF LIPOSOMES 2.1 Introduction ........................................................................................................... 72 2.1.1 Structure of liposomes ................................................................................72 2.1.2 Mechanism of liposome formation ............................................................73 2.1.3 Preparation of liposomes ............................................................................75 2.1.4 Release of entrapped agents from liposomes .............................................78 2.1.5 Size of liposomes ........................................................................................81 2.1.6 Size reduction of liposomes ....................................................................... 81 2.1.7 Entrapment and release of soluble solutes by liposomes ............................82 2.1.8 Surface tension of liposomes ......................................................................84 2.1.9 Viscosity of liposomes ............................................................................... 86 2.2 Materials.................................................................................................................87 2.3 Methods .................................................................................................................. 88 2.3.1 Purification of eggPC ................................................................................. 88 2.3.2 Preparation of MLVs ................................................................................. 88 2.3.3 Liposome analysis ...................................................................................... 89 2.3.4 Size reduction of prepared liposomes ....................................................... 89 2.3.4.1 Extrusion through polycarbonate membrane filters ................89 2.3.4.2 Probe sonication .......................................................................90 2.3.5 Liposomal entrapment and release of SCO ..............................................90 2.3.5.1 SCO standard curve
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