Pharmacokinetics of ketamine and three metabolites in Beagle dogs under sevoflurane vs. medetomidine comedication assessed by enantioselective capillary electrophoresis

Abstract

Ketamine is often used for anesthesia in veterinary medicine. One possible comedication is the sedative α-agonist medetomidine. Advantages of that combination are the compensation of side effects of the two drugs and the anesthetic-sparing effect of medetomidine. In vitro studies showed that medetomidine has an inhibitive effect on the formation of norketamine. Norketamine is the first metabolite of ketamine and is also active. It is followed by others like 6-hydroxynorketamine and 5,6-dehydronorketamine (DHNK). In an in vivo pharmacokinetic study Beagle dogs under sevoflurane anesthesia (mean end-tidal concentration 3.0±0.2%) or following medetomidine sedation (450μg/m) received 4mg/kg racemic ketamine or 2mg/kg S-ketamine. Blood samples were collected between 0 and 900min after drug injection. 50μL aliquots of plasma were pretreated by liquid-liquid extraction prior to analysis of the reconstituted extracts with a robust enantioselective capillary electrophoresis assay using highly sulfated γ-cyclodextrin as chiral selector and electrokinetic sample injection of the analytes from the extract across a short buffer plug without chiral selector. Levels of S- and R-ketamine, S- and R-norketamine, (2S,6S)- and (2R,6R)-hydroxynorketamine and S- and R-DHNK were determined. Data were analyzed with compartmental pharmacokinetic models which included two compartments for the ketamine and norketamine enantiomers and a single compartment for the DHNK and 6-hydroxynorketamine stereoisomers. Medetomidine showed an effect on the formation and elimination of all metabolites. Stereoselectivities were detected for 6-hydroxynorketamine and DHNK, but not for ketamine and norketamine.

Separation of hydroxynorketamine stereoisomers using capillary electrophoresis with sulfated β‐cyclodextrin and highly sulfated γ‐cyclodextrin

“…Thus, an injection time of 10 s with 7 kV was chosen for the final method. Finally, injections from liquid/liquid extracts prepared with a mixture of dichloromethane and ethylacetate (75:25%, v/v; ) or dichloromethane alone were compared. Although best analyte recovery was obtained with the solvent mixture, extraction with dichloromethane provided better peak shapes with electrokinetic sample injection .…”

“… and kept at –80°C until used for the in vitro incubation work. Animal plasma samples stemmed from two previously conducted ketamine studies which were executed with the permission of the respective Committee for Animal Experimentation . In the first trail, ponies received an i.v.…”

“…In the other trial, beagle dogs under sevoflurane anesthesia received an i.v. bolus of 4 mg/kg racemic ketamine . The plasma samples were kept frozen until analysis.…”

“…Due to high migration times, detected peaks are broad and their analysis becomes inaccurate. Because of stereoselectivities in metabolism, receptor affinity and antidepressive effects, the stereoselective separation of all metabolites of ketamine is important . This prompted us to find conditions to properly analyze the stereoisomers of hydroxylated norketamine metabolites by cationic CE.…”

Enantioselective capillary electrophoresis for pharmacokinetic analysis of methadone and 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine in equines anesthetized with ketamine and isoflurane

“…Microsoft Excel (Microsoft, Redmont, WA, USA) and SigmaPlot software version 12.5 (Systat Software, San Jose, CA, USA) were used for data evaluation and presentation, respectively. Pharmacokinetic modeling of methadone enantiomers was performed with the Phoenix WinNonlin 6.4 software (Certara: Implementing Translational Science, Cary, NC, USA) as described previously for ketamine and metabolites in plasma of Beagle dogs .…”