The single‐dose disposition kinetics of cefonicid were determined in clinically normal lactating goats (n = 6) after intravenous (IV), intramuscular (IM) and subcutaneous (SC) administration of a conventional formulation, and after subcutaneous administration of a long‐acting formulation (SC‐LA). Cefonicid concentrations were determined by high performance liquid chromatography with ultraviolet detection. The concentration–time data were analysed by noncompartmental pharmacokinetic methods. Steady‐state volume of distribution (Vss) and clearance (Cl) of cefonicid after IV administration were 0.14 ± 0.03 L/kg and 0.51 ± 0.07 L/h·kg, respectively. Following IM, SC and SC‐LA administration, cefonicid achieved maximum plasma concentrations of 14.46 ± 0.82, 11.98 ± 1.92 and 17.17 ± 2.45 mg/L at 0.26 ± 0.13, 0.42 ± 0.13 and 0.83 ± 0.20 hr, respectively. The absolute bioavailabilities after IM, SC and SC‐LA routes were 75.34 ± 11.28%, 71.03 ± 19.14% and 102.84 ± 15.155%, respectively. After cefonicid analysis from milk samples, no concentrations were found above LOQ at any sampling time. From these data, cefonicid administered at 20 mg/kg each 12 hr after SC‐LA could be effective to treat bacterial infections in lactating animals not affected by mastitis problems.

Rhodococcus equi is responsible for foal pneumonia worldwide, with a significant economic impact on the production and breeding of horses. In Chile, the first case was reported in 2000, and since then, its incidence has been increasing. Distinctive characteristics of R. equi as an intracellular pathogen in macrophages, emergence of virulence plasmids encoding surface lipoprotein antigens, and appearance of antibiotic resistance against macrolides and rifampicin have significantly complicated the treatment of R. equi pneumonia in foals. Therefore, in vitro susceptibility studies of first-line and newer antibiotics against R. equi are the first step to establishing effective treatments and optimizing new therapeutic options. The aim of the present study is to determine the susceptibility profile of fourteen strains of R. equi isolated from foals in Chile to several antibiotics of the macrolide group including azithromycin, amikacin, tildipirosin and gamithromycin as well as others such as rifampicin, doxycycline and ceftiofur. Identification of R. equi in collected isolates from foals in Chile has been performed by CAMP test and PCR based on detecting of the gene encoding the 16 S rRNA. The presence of genes encoding virulence plasmids was also determined using PCR. Results obtained have demonstrated presence of virulent R. equi strains in Chile. In vitro susceptibility pattern to different antibiotics has shown better results for doxycycline and rifampicin similar to previous studies performed. Current macrolides have been evaluated in order to consider alternative treatment options in a context of emerging resistance to classic macrolides and rifampicin, obtaining better results with gamithromycin (MIC range of 0.125 to 128 mg/ml) than with tildipirosin (MIC range of 16 to 128 mg/ml). An adequate diagnosis of bacterial susceptibility based on antibiograms is necessary to treat the Rhodococcus equi infection in foals.

Ovine respiratory complex is a significant cause of death in sheep flocks, where Pasteurella multocida is the most frequent microorganisms isolated from animals with pneumonia. There is an urgent need to refine the use of different antimicrobials to avoid the problem of antimicrobial resistance and optimize the control of this disease in ovine livestock. The first step in approaching this problem is gaining an insight into the antimicrobial susceptibility of ovine pathogens. This study evaluated the in vitro activity of tildipirosin, gamithromycin, oxytetracycline, and danofloxacin against Pasteurella multocida strains isolated from sheep with fibrinous pneumonia. The strains were incubated following Clinical and Laboratory Standards Institute (CLSI) standard conditions and also with a modified method by 25% supplementation with sheep serum. Minimum inhibitory concentrations (MIC) were determined using the broth microdilution technique. The lowest MIC90 under standard conditions and by supplementation with sheep serum was obtained with tildipirosin. Sheep serum significantly reduced tildipirosin, gamithromycin, and danofloxacin MIC values for Pasteurella multocida strains. In brief, the potency of tildipirosine, gamithromycin, and danofloxacin against Pasteurella multocida increases when sheep serum is added to the culture media.

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