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 (2.5 mg/kg/i.m). Animals in group 2 were also challenged intratracheally with lipopolysaccharide from Escherichia coli 3 h 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 17 days 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 (Tmax ) concentration was 6 h postdrug administration in PELF but 72 h post-tulathromycin administration for BELF. In group 2, the Tmax was seen at 24 h post-tulathromycin administration. The area under the concentration time curve (h*ng/mL) was 522 000, 348 000 and 1 290 000 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 (>4 days).