Terbutaline pharmacokinetics in cows: preliminary data.

The objective of this study was to determine the serum pharmacokinetics of terbutaline in healthy cows. In the initial experiment, terbutaline was administered once as an intravenous (i.v.) bolus to 6 near-term pregnant beef cows within 24 h after parturition at a low but therapeutically relevant dose, 5 microg/kg. A 2nd experiment was conducted in the same cows with a higher dose, 0.5 mg/kg, but an otherwise similar experimental design. The serum concentration of terbutaline was determined by means of high-performance liquid chromatography with fluorescence detection in both experiments. After i.v. administration of 0.5 mg/kg, the mean peak serum concentration, residence time, and half-life were 708.22 (standard deviation 509.6) ng/mL, 6.75 (3.6) min, and 6.93 (2.4) min, respectively. The results indicate that terbutaline is rapidly eliminated from the bloodstream after i.v. administration in cattle, falling below the assay's limit of detection 30 min after administration.