Pharmacokinetics of ketamine in plasma and milk of mature Holstein cows

Sellers, G., Lin, H. C., G. Riddell, M. G., Ravis, W. R., Lin, Y. J., Duran, S. H., Givens, M.D. Pharmacokinetics of ketamine in plasma and milk of mature Holstein cows. J. vet. Pharmacol. Therap. 33, 480-484. The purpose of this study was to evaluate the pharmacokinetics of ketamine in mature Holstein cows following administration of a single intravenous (i.v.) dose. Plasma and milk concentrations were determined using a high-performance liquid chromatography assay. Pharmacokinetic parameters were estimated using a noncompartmental method. Following i.v. administration, plasma Tmax was 0.083 h and plasma Cmax was 18 135 ± 22 720 ng/mL. Plasma AUC was 4484 ± 1,398 ng·h/mL. Plasma t[fraction one₋half]β was 1.80 ± 0.50 h and mean residence time was 0.794 ± 0.318 h with total body clearance of 1.29 ± 0.70 L/h/kg. The mean plasma steady-state volume of distribution was calculated as 0.990 ± 0.530 L/kg and volume of distribution based on area was calculated as 3.23 ± 1.51 L/kg. The last measurable time for ketamine detection in plasma was 8.0 h with a mean concentration of 24.9 ± 11.8 ng/mL. Milk Tmax was detected at 0.67 ± 0.26 h with Cmax of 2495 ± 904 ng/mL. Milk AUC till the last time was 6593 ± 2617 ng·h/mL with mean AUC milk to AUC plasma ratio of 1.99 ± 2.15. The last measurable time that ketamine was detected in milk was 44 ± 10.0 h with a mean concentration of 16.0 ± 9.0 ng/mL.