OBJECTIVE To determine the pharmacokinetics of tilmicosin after oral administration of a single dose of tilmicosin base in swine. METHODS 10 healthy swine. METHODS Tilmicosin base was administered via stomach tube at a single dose of 20 mg/kg (n = 5) or 40 mg/kg (5). Blood samples were obtained from a jugular vein immediately before and at 10, 20, and 30 minutes and 1, 2, 3, 4, 6, 8, 12, 24, 36, 48, 72, 96, and 120 hours after administration of tilmicosin. Tilmicosin concentrations in serum were quantified by use of a high-performance liquid chromatography procedure with UV light. Data for tilmicosin concentrations versus time were analyzed by use of compartmental and noncompartmental methods. RESULTS Tilmicosin concentrations in serum decreased in a biexponential manner after oral administration. Mean +/- SD values for absorption half-lives were 1.49 +/- 0.23 hours and 1.64 +/- 0.40 hours, distribution half-lives were 2.96 +/- 0.58 hours and 3.20 +/- 0.76 hours, elimination half-lives were 25.26 +/- 8.25 and 20.69 +/- 5.07 hours, peak concentrations were 1.19 +/- 0.30 microg/mL and 2.03 +/- 0.28 microg/mL, and time to peak concentrations was 3.12 +/- 0.50 hours and 3.48 +/- 0.77 hours after oral administration of tilmicosin base at a single dose of 20 or 40 mg/kg, respectively. CONCLUSIONS In swine, tilmicosin was rapidly absorbed and slowly eliminated after oral administration of a single dose of tilmicosin base powder.