Development and comparative anti-microbial evaluation of lipid nanoparticles and nanoemulsion of Polymyxin B

Polymyxin B is a decapeptide, mainly used for the treatment of gram-negative bacteremia. It was anticipated that a prolongation of release may lead to a more efficacious therapy. Lipid nanoparticles and nanoemulsion were formulated and comparatively evaluated for their properties. Lipid nanoparticles of Polymyxin B Sulphate with a mean particle size of 186.9 nm (Polydispersity Index 0.235) were prepared by nano-precipitation technique and nanoemulsion was prepared under the conditions of spontaneous formation with a mean globule size 125.0 nm (Polydispersity Index 0.291). The lipid nanoparticles were screened for lipid load from 0.1-1% along with 1-10% surfactant while in the optimization of nanoemulsion different ratios of oil, surfactant, and co-surfactant were evaluated. The developed systems were taken up for comparative anti-microbial study against a sensitive strain of E. coil using Turbidimetry as the method for monitoring the growth of microorganisms in a time dependent manner. Results of the study using ANOVA revealed an initial comparable activity with no statistical difference between the free drug, lipid nanoparticles, and the nanoemulsion. The anti-microbial effect was significantly sustained by lipid nanoparticles over a period of 18 hr but could not be sustained in case of nanoemulsion after 12 hr. Further, in order to assess anti-microbial activity of the developed delivery templates, a similar study was carried out using the lipid nanoparticles and nanoemulsion without the incorporation of drug. The results showed only a mild anti-microbial action for drug-free lipid nanoparticles but significant activity was exerted by drug-free nanoemulsion against plain drug throughout the study. It was concluded that the developed lipid nanoparticles and nanoemulsion are promising delivery vectors for the anti-microbial drugs. Further, lipid nanoparticles could give an initial as well as sustained effect while the nanoemulsion was capable of exerting potent effect for a shorter period of time.