Enantioselective CE analysis of hepatic ketamine metabolism in different species in vitro

Abstract

Ketamine, an injectable anesthetic and analgesic consisting of a racemic mixture of S-and R-ketamine, is routinely used in veterinary and human medicine. Nevertheless, metabolism and pharmacokinetics of ketamine have not been characterized sufficiently in most animal species. An enantioselective CE assay for ketamine and its metabolites in microsomal preparations is described. Racemic ketamine was incubated with pooled microsomes from humans, horses and dogs over a 3 h time interval with frequent sample collection. CE data revealed that ketamine is metabolized enantioselectively to norketamine (NK), dehydronorketamine and three hydroxylated NK metabolites in all three species. The metabolic patterns formed differ in production rates of the metabolites and in stereoselectivity of the hydroxylated NK metabolites. In vitro pharmacokinetics of ketamine N-demethylation were established by incubating ten different concentrations of racemic ketamine and the single enantiomers of ketamine for 8 min and data modeling was based on Michaelis-Menten kinetics. These data revealed a reduced intrinsic clearance of the S-enantiomer in the racemic mixture compared with the single S-enantiomer in human microsomes, no difference in equine microsomes and the opposite effect in canine microsomes. The findings indicate species differences with possible relevance for the use of single S-ketamine versus racemic ketamine in the clinic.

Chiral electromigration techniques in pharmaceutical and biomedical analysis

“…Thormann and colleagues have extensively studied the in vitro and in vivo metabolism of the anesthetic drug ketamine in equine plasma [129,130], dog plasma [131], equine, canine and human liver microsomes [132,133] and single human CYP isoenzymes [134]. The drug undergoes hepatic first-pass metabolism, the major pathways include N-demethylation to norketamine followed by hydroxylation and further glucuronidation or formation of 5,6-dehydronorketamine.…”

Stereoselective determination of drugs and metabolites in body fluids, tissues and microsomal preparations by capillary electrophoresis (2000–2010)

“…Systems studied include sulfoxidation [128,130,137], N-oxidation [129], hydroxylation [108,114,131,132,[134][135][136], dealkylation [131,134,135,138,139], carboxylation [133] and ketoreduction [119] reactions in presence of human or rat liver microsomes (HLM or RLM, respectively), human or rat liver S9 fraction, human liver cytosol (HLC), recombinant human single cytochrome P450 (CYP) enzymes or recombinant human single flavin monooxygenase (FMO) enzymes (Table 4). Not included in Table 4 are our investigations dealing with the metabolism of ketamine in different species which includes the N-demethylation to norketamine followed by hydroxylation of norketamine [156,[166][167][168][169] (Table 6 and Section 3.4). Cimetidine [128], fenbendazole [130] and thiobencarb [137] are prochiral drugs which undergo metabolism by primary oxidation of the sulfide moiety to their sulfoxides, compounds that exhibit a sulfur stereogenic center, and by a second oxidation to the achiral sulfon derivative.…”

“…Compared to the previous decade, during which mostly uncharched CDs were employed [26], we noted a strong increase of the use of charged CDs. S-␤-CD, with 7-11 mol sulfate/mol ␤-CD, was most often used [58,60,63,69,71,79,80,83,95,97,99,101,108,110,118,123,131,134,135,139,[154][155][156][157][158][159][160][161][162][163][164][165][166][167][168][169] whereas the better defined highly sulfated CD derivatives (HS-␤-CD and HS-␥-CD [170]) were only used in a few assays [50,51,72,111,144,145]. These and other selectors, such as phosphated-␥-CD (PH-␥-CD) [94,106,126], carboxymethyl-␤-CD (CM-␤-CD) or carboxymethyl-␥-CD (CM-␥-CD) …”

“…Hepatic ketamine metabolism in different species in vitro [167] rac-K, S-K NK Equine, canine and human liver microsomes…”

“…As with our previous compilation 10 years ago [26], insight into the achievements is presented via distinction between enantiomer analysis in fortified body fluids (Table 1), body fluids and tissues of humans and animals (Tables 2 and 3), in vitro preparations (Table 4) and in forensic biosamples (Table 5 [ ). Furthermore, the stereoselective CE work associated with a multidisciplinary ketamine project is presented separately (Table 6 [ [154][155][156][157][158][159][160][161][162][163][164][165][166][167][168][169]). Major focus is given on systems in which stereoisomers of parent drug and metabolites are analyzed together in one run.…”