Preparation and stability study of norfloxacin-loaded solid lipid nanoparticle suspensions

This work aims to develop norfloxacin-loaded solid lipid nanoparticle (NFX-SLN) suspensions as a novel formulation. NFX-SLN suspensions were prepared by hot homogenization and ultrasonic technique. The stability of the suspensions was studied after stored at 4°C and room temperature from 3 to 9 months. The physicochemical characteristics of the NFX-SLN, in vitro release patterns, in vitro antibacterial activity and in vivo therapeutic efficacy in mice after infection with Escherichia coli were conducted and used to evaluate the stability of the suspension. The results showed that the mean diameter (MD), polydispersity index (PDI), zeta potential (ZP) and loading capacity (LC) of nanoparticles were 250±5 nm, 0.256±0.065, -31.1±1.85 mV and 9.63±0.16%, respectively. After 9 months of storage at 4°C, the NFX-SLN showed no significant changes in MD, PDI and LC except a miner change in ZP. Moreover, the stored suspension displayed same sustained release patterns and in vitro sustained bactericidal activities as that of the fresh preparation. In vivo therapeutic results revealed that the stored suspension had similar enhanced therapeutic efficacy as the fresh preparation compared with native drug. At room temperature the formulation was stable for 3 months, but the LC, ZP and PDI changed and the suspension displayed accelerated release and weakened in vitro antibacterial activity after 6 months. These results demonstrate that NFX-SLN suspensions could be a promising formulation for enhanced pharmacological activity of norfloxacin and were stable at 4°C and less stable at room temperature.