Pulmonary pharmacokinetics of tulathromycin in swine. Part 2: Intra-airways compartments

The objective of this study was to assess the pharmacokinetics of tulathromycin in pulmonary and bronchial epithelial lining fluid (PELF and BELF) from pigs. Clinically healthy pigs were allocated to two groups of 36 animals each. All animals were treated with tulathromycin (2.5mg/kg/i.m). Animals in group 2 were also challenged intratracheally with lipopolysaccharide from Escherichia coli 3h prior to tulathromycin administration. Both PELF and BELF samples were harvested using bronchoalveolar lavage fluid and bronchial micro-sampling probes, respectively. Samples were taken for 17days post-tulathromycin administration. No statistical differences in the concentration of tulathromycin were observed in PELF between groups. The concentration vs. time profile in BELF was evaluated only in Group 1. Tulathromycin distributed rapidly and extensively into the airway compartments. The time to maximal (T-max) concentration was 6h postdrug administration in PELF but 72h post-tulathromycin administration for BELF. In group 2, the T-max was seen at 24h post-tulathromycin administration. The area under the concentration time curve (h*ng/mL) was 522000, 348000 and 1290000 for PELFGroup-1, PELFGroup-2, and BELFGroup-1, respectively. Tulathromycin not only distributed rapidly into intra-airway compartments at relatively high concentrations but also resided in the airway lining fluid for a long time (>4days).