The aim of this study is to prepare mucopenetrating nanoparticles of the antibiotic cefixime and perform their physical characterisation after pegylation and lyophilization, as well as to determine the percentage of drug in the most fitting nanoparticles to achieve maximum bioavailability and, according to that, a better therapeutic effect. Moreover, since in the experimental part of the work for cefixime determination was used HPLC method, prior to the tests it has been carried out its development and validation. Nanoparticles were formed using Gantrez™ AN-169, anhydrous polymer and then. PEGylated with PEGs of different molecular weight; PEG 4000, PEG 6000 and PEG 000. PEGylation stabilizes a suspension of nanoparticles which would otherwise swell in aqueous medium and dissolve. Nanoparticle size does not exceed 200 nm, which meets the criteria for achieving optimal therapeutic effect. The amount of zeta potential in all three samples of PEGylated nanoparticles is greater than -40 mV, but due to the negative charges on the mucins, it is not expected to bind the nanoparticles in the mucus. As hypothesized, polydispersity index, measured after coating nanoparticles was less than 0,2, and it is, thereby, it is confirmed that the system is monodispersed. When nanoparticles were PEGylated with PEG 6000, the increase in polydispersity index is not statistically significant and the administration of these nanoparticles noticing the highest incorporation percentage of cefixime, of about 10%. The abovementioned facts show that the nanoparticles coated with PEG 6000 most appropriate system for the further research.