Columbano, Angela; (2001) Modification of microparticle surfaces by use of alkylpolyglycoside surfactants. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The purpose of the PhD was to study the interactions of alkylpolyglycoside surfactants (APGs) with a model hydrophobic and a model hydrophilic drug, in part to determine whether these surfactants improve the stability of suspensions in metered dose inhalation systems (MDI). The adsorption of APGs on a hydrophobic drug (micronised beclomethasone dipropionate, BDP) from water was studied and the BDP-APG microparticles characterised. It was found that the APG caused changes in the morphology and size of the drug. It was also observed that the surfactants with the highest purity allowed the transition from the original anhydrous form of BDP to the monohydrate, whereas the monohydrate could not form in the presence of aqueous solutions of the technical grades of APGs. This indicated that technical APGs interacted in a more homogeneous way with the surface of BDP particles. The study of the surface energy of BDP by inverse gas chromatography (IGC) before and after adsorption of the APGs showed that presence of the surfactants modified the surface energy of the drug. The changes were linked to the amount of surfactant adsorbed, to the nature of the surfactant and to the way it interacted with the surface of the drug. Microparticles of a model hydrophilic drug (salbutamol sulphate) and APGs were prepared by spray drying drug-surfactant solutions, and by adsorption of APGs to the micronised form of the drug from an organic solvent. Their characteristics in terms of morphology, particles size and, when applicable amorphous content, were investigated. Through IGC it was found that the APGs modified the surface energy parameters of the drug, indicating that the surfactant was on the surface of the particles. Finally, the suspension stability of the microparticles of drug-alkylpolyglycosides in MDI propellants (HFA 227 and 134a) was examined by optical suspension characterisation. The results of a short-term stability study were encouraging especially for the BDP-APG particles, which showed a clear superiority to the drug alone. This confirmed the possibility of using APGs to help to stabilise MDI suspensions, even though the surfactants are not soluble in the propellants.

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