Drug-polymer interaction in relation to surface tension and polymer properties

Sammanfattning: Polymers are important in a variety of pharmaceutical applications. Many of them are derived from cellulose but there are several biological sources of importance for their production. Polymers display a very wide diversity of properties which makes a detailed characterization necessary. The investigated polymers are more or less surface active due to the presence of hydrophilic and hydrophobic parts. They show surface activity at very low concentrations which makes them useful as stabilizers in suspensions and emulsions. The surface tension measurements were performed by the pendant drop method.The surface activity and the cloud point (CP) are related to each other. These parameters depend on the hydrophilic/hydrophobic balance of the polymer. The time dependence of surface tension is mainly related to the concentration in the dynamic region (2-10 ppm). The half-life of the surface tension (t1/2) at these concentrations was found to be inversely correlated to the diffusion coefficient and to the square of the bulk concentration, which is expected for a diffusion process. Furthermore, t1/2 was related to the intrinsic viscosity of the polymers.The in situ colonic effective permeability of fluvastatin in the rat was found to be inversely proportional to the surface tension of fluvastatin.The interaction between charged amphiphiles and oppositely charged polymers was investigated by surface tension measurements since surface activity is an important property of pharmaceutical formulation. The adsorption of charged amphiphiles to oppositely charged polyelectrolytes involve charge to charge interaction at low amphiphile concentration. An increase in amphiphile concentration is followed by a cooperative increase in adsorption at a certain concentration due to hydrophobic interaction between already adsorbed amphiphiles. The strength of the interaction is related to the hydrophobicity of the amphiphile. Also the charge density isimportant since the distance between the charges influence the concentration where the hydrophobic interaction starts.