Particulate drug interactions with polymeric and elastomeric valve components in suspension formulations for metered dose inhalers

PurposeTo characterise the adhesive interactions between three pulmonary active pharmaceutical ingredient (API) materials and the components of pressurised metered dose inhalers (pMDIs) obtained from two commercially available products (termed ‘Prod-1’ and ‘Prod-2’). This is of potential interest, as a greater understanding of the interactions between specific APIs and surfaces may aid manufacturers in component selection during pMDI system development.MethodsThe theoretical work of adhesion (ΔG132) for each API–pMDI component interaction was calculated using the surface component analysis (SCA) approach. These results were correlated with corresponding API–pMDI component separation energy measurements determined using colloid probe AFM.ResultsStrong correlations existed between separation energy and the ΔG132 parameters where the polar contribution was accounted for. This highlighted the adhesive influence of polar surface energy on each interaction in this study. Generally the largest adhesive interactions involved APIs and pMDI components which have a bipolar surface energy (i.e. both γ− and γ+ >1 mJ m−2).ConclusionsFor each API–pMDI interaction in this study, the polar component of surface energy has the greater influence on adhesive events. The bipolar surface energetics of certain APIs and pMDI components were deemed responsible for the increased adhesive interactions observed with these materials. This study highlights that different materials can have different effects on the adhesive interactions with particulate APIs; information that could aid the manufacturer in producing more effective and efficient pMDI systems.