Preservation of Suspensions in the Presence of Surface Active Agents
Preservatives are added to pharmaceutical preparations to prevent the growth of contaminants which might be introduced during preparation or use. The performance of the added preservative however depends very much on the properties of the other ingredients of formulation. Surface-active agents which are employed for various purposes in pharmaceutical preparations have been found to influence the activity of preservatives in creams, emulsions and related preparations. These surface - active agents are being increasingly used as wetting and flocculating agents in the preparation of pharmaceutical suspensions but there is very little information about their interactions, if any, with other components of pharmaceutical suspensions hence the importance of this study. A spectrophotometric investigation of the adsorption of Triton x45, a non-ionic surfactant and PNE, an anionic surfactant, by some powders and starches was carried out. The results show that both surfactants were adsorbed by the powders used in this study through one of several mechanisms, It was also observed that the extent and pattern of adsorption of both PNE and Triton x45 were changed in the presence of methyl and propylpara-hydroxy benzoate The effectiveness of preservation of suspensions by methyl and propyl para hydroxybenzoates was also evaluated by the estimation of contact killing time. These evaluations were conducted in the absence and presence of surfactants and suspended solids using Escherichia coli as the test organism. A significant reduction in the activity of the preservatives by suspended solids was observed. Furthermore, Triton x45 was found to enhance the activity of the preservatives whilst there was no significant change in their activity in the presence of PNE.