Plasma and red blood cells concentration profiles of ketamine after single intravenous administration in an anaesthetic protocol in horses

The aim of this study was to describe the concentration profile of ketamine in plasma and red blood cells following an intravenous (IV) bolus in the horse. Ten healthy standardbred horses (two males and height females) 7.7 ± 4.6 (mean value ± SD) years old and weighting 380 ± 21 kg (mean value ± SD) were recruited. The horses were premedicated with acepromazine (0.04 mg·kg−1·IV). Fifteen minutes later they received romifidine (0.08 mg·kg−1·IV), and 5 minutes after they were administered midazolam (0.06 mg·kg−1·IV). Immediately, anaesthesia was induced by ketamine (2.2 mg·kg−1·IV). Venous blood samples were collected at scheduled time points. Plasma and red blood cells (RBCs) concentration of ketamine was assayed using a high performance liquid chromatographic method (HPLC/UV-DAD). The high mean recovery rates, the high sensitivity, the good linearity, suggest a clinical applicability of the analytical method. A bicompartmental model resulted as the most appropriate to describe the ketamine concentration—time profile for both plasma and RBCs. The fitted regression line between ketamine plasma concentrations and RBC concentrations supports the good correlation between ketamine concentrations in plasma and in RBCs. The kinetic parameters of ketamine calculated for RBC are equal or very similar to the plasma ones. The study confirms the kinetic behaviour of ketamine used in the horse as anaesthetic inducers in routine surgery. Finally, the bicompartmental model well describes the ketamine profile also in RBCs, that it is very close to the plasma profile, underlining the great importance of RBCs as blood subcompartment.