Biostatic activity of binary mixtures of local anesthetics and preservatives

ABSTRACT

The biostatic activity of binary mixtures of five different preservatives with cinchocaine, amethocaine, amylocaine, lignocaine, and procaine was determined against Staphylococcus aureus, Escherichia coli and Saccharomyces cervesiae. The preservatives used were cetrimide, chlorhexidine, chlorocresol, phenoxyethanol and phenylmercuric nitrate. The sensitivity of the three test organisms towards the different combinations varied to some extent. While 19, 17 and 18 out of 25 combinations were synergistic with E. coli, S. aureus and S. cervesiae, respectively, 2, 6 and 8 combinations were antagonistic against the same organisms. Out of the total 75 local anesthetic preservative combinations studied, 55 showed synergistic biostatic activity, while 12 displayed antagonism. The remaining 8 combinations were additive in action. The number of synergistic combinations were as follows Amylocaine, 9, procaine, 9, amethocaine, 11, cinchocaine, 12 and lignocaine 13. More antagonistic combinations were observed with procaine [5], followed by amylocaine [3], then the other three local anesthetics. Regarding the preservative component of the local anesthetic preservative combinations, those containing chlorocresol or phenoxyethanol were mainly synergistic [13-14 combinations out of 15 each] and showing no antagonism. Although local anesthetics mixed with cetrimide, chlorhexidine or phenylmercuric nitrate had synergistic combinations, there antagonistic ones were 1, 5 and 6, respectively, for the preservatives mentioned