Interaction of polyhexamethylene biguanide hydrochloride (PHMB) with phosphatidylcholine containing o/w emulsion and consequences for microbicidal efficacy and cytotoxicity.

Oil-in-water (o/w) emulsions containing egg yolk phosphatidylcholine (EPC) were combined with aqueous polyhexamethylene biguanide hydrochloride (PHMB). The PHMB concentration in the aqueous phase was estimated by filtration centrifugation experiments. In parallel, PHMB concentration was assessed utilizing cytotoxicity assays (neutral red) on cultured murine fibroblasts (L929 cells) and tests of bactericidal efficacy on either Pseudomonas aeruginosa or Staphylococcus aureus. Biological tests were performed in cell culture medium. Filtration centrifugation experiments demonstrated much higher aqueous PHMB concentrations than did the assays for biologically effective PHMB. Therefore, biological test systems should preferably be used to verify effective PHMB concentrations. Tests of microbicidal efficacy in which the same 0.05% PHMB o/w emulsion was re-used 8 times revealed a drug delivery system activated by the presence of test bacteria.