Dynamics of clomethiazole edisylate interaction with plastic infusion systems

The dynamics of the interaction of clomethiazole edisylate (1) with polyvinyl chloride and cellulose propionate, the main plastics used in the manufacture of infusion bags and sets, was examined. An experimental system in which the plastic was either open or closed to the environment was used to determine the relative contribution of the sorption and permeation processes to loss from solutions of clomethiazole edisylate (I) in contact with the plastic infusion systems. Sorption by the plastic infusion materials accounted for most of the drug loss, while permeation into the external environment accounted for the remainder. The sorption and permeation into and through polyvinyl chloride was temperature dependent. The diffusion coefficient and permeation rate constant both increased with temperature, while the polyvinyl chloride-water partition coefficients were independent of temperature. The activation energy for the diffusion in polyvinyl chloride was 13.5 kcal/mol. The permeability of the infusion bag plastic and the evaporation across an unstirred air boundary layer adjacent to the external surface of the plastic both appeared to contribute to the overall diffusional resistance encountered in the permeation process. The plastic-water partition coefficients are independent of initial concentration, suggesting that the concentration-dependent loss of the drug from solutions stored in plastic infusion bags and burets is a result of the greater diffusivity of the drug in the plastic at the higher initial concentrations. Plasticization of the polymers by the drug is indicated by the increase in the diffusivity of the drug in polyvinyl chloride and cellulose propionate, the increase in the rate and extent of sorption of a radiolabeled marker (diazepam) by the plastic, and the decreased stiffness of polyvinyl chloride exposed to higher concentrations of the drug.