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Distribution and antimicrobial activity of preservatives in solubilized and emulsified systems

University of British Columbia

Until recently, evaluation of the effectiveness of preservatives in solubilized and emulsified systems has depended largely on time-consuming microbiological techniques. Mathematical models have now been developed which enable the amount of preservative necessary for adequate preservation to be calculated. These mathematical models have been derived on the assumption that the antimicrobial activity of preservative in solubilized and emulsified systems is largely a function of the free preservative concentration in the aqueous phase. In this work, a physicochemical and microbiological evaluation was made to test the validity of the above assumption and to study the possible effects of changes in surfactant concentration and oil-water ratio on the antimicrobial activity of preservative in solubilized and emulsified systems. Some weaknesses of the earlier models were pointed out. In particular, the concept of the capacity of the system to resist the changes in effective free preservative concentration was developed. The permeability of cellophane membranes to the nonionic surfactant cetomacrogol was investigated using equilibrium dialysis, dynamic dialysis, and an ultrafiltration technique. Cellophane and silicone rubber membranes were compared in an equilibrium dialysis study of the interaction of chlorocresol with nonionic surfactants. The magnitude of errors introduced into the binding parameters using cellophane membrane were related to the permeability of the membranes to the nonionic surfactants and to changes in volume and in surfactant concentration which occurred" as a result of osmotic differential across the membrane. The diafiltration technique was evaluated for the interaction of benzoic acid with cetomacrogol. The results of the diafiltration technique were compared with those obtained using the equilibrium dialysis technique. Various technical artifacts of the diafiltration technique were pointed out. Interaction of preservative mixtures with the nonionic surfactant cetomacrogol was studied using the equilibrium dialysis technique. Attempts to correlate the data with theory of competitive protein binding were unsuccessful. The interaction of chlorocresol with certain nonionic surfactants and their mixtures was studied using the equilibrium dialysis technique. Binding parameters which characterized the interaction of the preservative with each individual surfactant were used to predict the binding behaviour of surfactant mixtures. Various factors affecting the distribution of preservatives between oil .and water and the interaction between preservatives and surfactants are discussed. These factors were related to the problem of the distribution of a preservative in oil and water emulsion systems. Methodology used to evaluate the various physicochemical parameters and the antimicrobial activity is reviewed, and equations for representing the results are discussed. The Millipore filtration method was compared with a pour-plate technique for the viable counting of E. eoli. The bactericidal activity of chlorocresol in aqueous cetomacro-gol solutions and liquid paraffin emulsions of varying oil-water ratios against coli was studied using a viable count method. The microbiological results were related with the physicochemical models of preservative distribution in solubilized and emulsified systems.

Text

2010-01-28

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http://hdl.handle.net/2429/19230

Pharmaceutical Sciences

University of British Columbia

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