This article is available online at http://dmd.aspetjournals.org ABSTRACT:Ketamine is a widely used drug for its anesthetic and analgesic properties; it is also considered as a drug of abuse, as many cases of ketamine illegal consumption were reported. Ketamine is Ndemethylated by liver microsomal cytochrome P450 into norketamine. The identification of the enzymes responsible for ketamine metabolism is of great importance in clinical practice. In the present study, we investigated the metabolism of ketamine in human liver microsomes at clinically relevant concentrations. Liver to plasma concentration ratio of ketamine was taken into consideration. Pooled human liver microsomes and human lymphoblastexpressed P450 isoforms were used. N-demethylation of ketamine was correlated with nifedipine oxidase activity (CYP3A4-specific marker reaction), and it was also correlated with S-mephenytoin N-demethylase activity (CYP2B6-specific marker reaction). Orphenadrine, a specific inhibitor to CYP2B6, and ketoconazole, a specific inhibitor to CYP3A4, inhibited the N-demethylation of ketamine in human liver microsomes. In human lymphoblast-expressed P450, the activities of CYP2B6 were higher than those of CYP3A4 and CYP2C9 at three concentrations of ketamine, 0.005, 0.05, and 0.5 mM. When these results were extrapolated using the average relative content of these P450 isoforms in human liver, CYP3A4 was the major enzyme involved in ketamine N-demethylation. The present study demonstrates that CYP3A4 is the principal enzyme responsible for ketamine N-demethylation in human liver microsomes and that CYP2B6 and CYP2C9 have a minor contribution to ketamine N-demethylation at therapeutic concentrations of the drug.Ketamine is a N-methyl-D-aspartate receptor antagonist used in clinical practice since 1970 for its anesthetic, sedative, and analgesic properties. It is frequently used for induction of anesthesia in short term surgical operations, in maintaining anesthesia with other anesthetic agents, and as a postoperative pain relief agent in intensive care units (Nimmo and Clements, 1981;White et al., 1982). In recent years, there is increasing evidence of ketamine abuse, many cases of illegal ketamine consumption, and dependence was reported (Jansen and Darracot-Cankovic, 2001;Moore et al., 2001).Ketamine is N-demethylated by cytochrome P450 (P450 1 ) enzymes in the liver into norketamine (Fig. 1). In humans and animals, norketamine (NK) is considered as the major metabolite (Kaka and Hayton, 1980;Woolf and Adams, 1987), and it may contribute to the analgesic effect following ketamine administration (Shimoyama et al., 1999). In a recent study (Yanagihara et al., 2001), the human liver microsomal enzyme CYP2B6 was identified as the main P450 isoform responsible for the N-demethylation of ketamine in pooled human liver microsomes obtained from 10 donors, at a ketamine concentration of 0.005 mM. The expression of CYP2B6 is very low in comparison with other P450 isoforms (Ͻ1% of total P450). In addition, CYP2B6 shows a large interindiv...

Background: Polymorphic thiopurine S-methyltransferase (TPMT) is a major determinant of thiopurine toxicity.Methods: We extracted 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) from erythrocytes with perchloric acid and converted them to 6-thioguanine (6-TG) and a 6-methylmercaptopurine (6-MMP) derivative during a 60-min acid hydrolysis step. The liquid chromatography system consisted of a C 18 column with an ammonium acetate-formic acid-acetonitrile buffer. 8-Bromoadenine was the internal standard. Analytes were measured with positive ionization and multiple reaction monitoring mode. With PCR-restriction fragment length polymorphism analysis and TaqMan allelic discrimination, common TPMT alleles (*1, *2, *3A, *3B, *3C) were determined in 31 792 individuals. We used perchloric acid extraction, acid hydrolysis, and HPLC with ultraviolet detection to measure erythrocyte 6-TG and 6-MMP nucleotide concentrations in 6189 patients with inflammatory bowel disease receiving azathioprine/6-mercaptopurine therapy. Results: Intra-and interday imprecision were <10% at low and high analyte concentrations. The conversion of

6-thioguanine (6-TGN) and methyl 6-mercaptopurine nucleotides (Me6-MPNs) are the two major metabolites found in erythrocytes after administration of azathioprine. In an attempt to understand the role of these metabolites in the pharmacologic and toxic activity of thiopurines, we have developed a HPLC method for the simultaneous determination of 6-TGNs and Me6-MPNs in erythrocytes. A simple and rapid treatment procedure based on deproteinization by perchloric acid with dithiothreitol is described. The nucleotides were hydrolyzed to their own bases by heating the sample for 45 min at 100 °C. During acid hydrolysis Me6-MP was converted into a compound analyzed on a Purospher RP18-e column with 0.02 mol/L dihydrogenophosphate buffer–methanol as eluents. With this procedure, mean recoveries of 73.1% and 84.0% for 6-TGN and Me6-MPN derivatives, respectively, were found

We conclude that the extent of hydroxylation in propofol metabolism was higher than in previous findings after administration of anaesthetic doses of propofol. Moreover, the ratio between hydroxylation and glucuronidation of propofol is subject to an inter-patient variability but this does not correlate with the dose of propofol. However, the variation of the metabolite profile observed in the present report does not seem to indicate an extended role of metabolism in pharmacokinetic variability.

Pharmacokinetic variables of ketamine in intensive care patients are greater than in healthy volunteers and in surgical patients. The increase in the volume of distribution is greater than the increase in clearance, resulting in a longer estimated half-life of ketamine in this patient group.