Tilmicosin- and florfenicol-loaded hydrogenated castor oil-solid lipid nanoparticles to pigs: Combined antibacterial activities and pharmacokinetics

The combined antibacterial effects of tilmicosin (TIL) and florfenicol (FF) against Actinobacillus pleuropneumoniae (APP) (n=2), Streptococcus suis (S.suis) (n=2), and Haemophilus parasuis (HPS) (n=2) were evaluated by chekerboard test and time-kill assays. The pharmacokinetics (PKs) of TIL- and FF-loaded hydrogenated castor oil (HCO)-solid lipid nanoparticles (SLN) were performed in healthy pigs. The results indicated that TIL and FF showed synergistic or additive antibacterial activities against APP, S.suis and HPS with the fractional inhibitory concentration (FIC) ranging from 0.375 to 0.75. The time-kill assays showed that 1/2 minimum inhibitory concentration (MIC) TIL combined with 1/2 MIC FF had a stronger ability to inhibit the growth of APP, S.suis, and HPS than 1 MIC TIL or 1 MIC FF, respectively. After oral administration, plasma TIL and FF concentrations could maintain about 0.1g/ml for 192 and 176hr. The SLN prolonged the last time point with detectable concentrations (T-last), area under the concentration-time curve (AUC(0-t)), elimination half-life (T-1/2ke), and mean residence time (MRT) by 3.1, 5.6, 12.7, 3.4-fold of the active pharmaceutical ingredient (API) of TIL and 11.8, 16.5, 18.1, 12.1-fold of the API of FF, respectively. This study suggests that the TIL-FF-SLN could be a useful oral formulation for the treatment of APP, S.suis, and HPS infection in pigs.