The adhesion force of micronized Salmeterol Xinafoate particles to pharmaceutically relevant surface materials

Abstract
The adhesion of micronized Salmeterol Xinafoate to various surface materials has been investigated by the centrifuge technique. The adhesion of the drug to these materials used for manufacture and storage of interactive mixtures of the drug and milled lactose monohydrate depends on different properties of the surfaces. A longer contact with polyvinylchloride, polyethylene or aluminium surfaces, or a contact with these surfaces under mechanical pressure should be avoided because the adhesion force between the drug and these surfaces is much higher than between the drug and excipient particles. Hence detachment and a consequent loss of drug in the formulation could occur. Such a problem does not appear to exist for the contact with polyhydroxymethylene surfaces. Characteristics of the surface materials such as the surface free energy (acid - base concept), surface roughness and Young's modulus were determined and related to the experimental results. The work of adhesion appeared to have a very important influence on the adhesion forces measured. About 20% of the work of adhesion was due to acid - base interactions. The larger the work of adhesion, the stronger was the adhesion between the particles and the surfaces in contact. Surface roughness reduced the adhesion force, and stiffer materials (having a high Young's modulus) were found to have a lower adhesion force to the drug particles.

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