Preparation, characterization, and pharmacokinetics of tilmicosin- and florfenicol-loaded hydrogenated castor oil-solid lipid nanoparticles.

To effectively control bovine mastitis, tilmicosin (TIL)- and florfenicol (FF)-loaded solid lipid nanoparticles (SLN) with hydrogenated castor oil (HCO) were prepared by a hot homogenization and ultrasonication method. In vitro antibacterial activity, properties, and pharmacokinetics of the TIL-FF-SLN were studied. The results demonstrated that TIL and FF had a synergistic or additive antibacterial activity against Streptococcus dysgalactiae, Streptococcus uberis, and Streptococcus agalactiae. The size, polydispersity index, and zeta potential of nanoparticles were 289.1 ± 13.7 nm, 0.31 ± 0.05, and -26.7 ± 1.3 mV, respectively. The encapsulation efficiencies for TIL and FF were 62.3 ± 5.9% and 85.1 ± 5.2%, and the loading capacities for TIL and FF were 8.2 ± 0.6% and 3.3 ± 0.2%, respectively. The TIL-FF-SLN showed no irritation in the injection site and sustained release in vitro. After medication, TIL and FF could maintain about 0.1 µg/mL for 122 and 6 h. Compared to the control solution, the SLN increased the area under the concentration-time curve (AUC0-t ), elimination half-life (T½ke ), and mean residence time (MRT) of TIL by 33.09-, 23.29-, and 37.53-fold, and 1.69-, 5.00-, and 3.83-fold for FF, respectively. These results of this exploratory study suggest that the HCO-SLN could be a useful system for the delivery of TIL and FF for bovine mastitis therapy.