Background Ketamine has rapid antidepressant effects lasting as long as 1 week in patients with major depressive disorder (MDD) and bipolar depression (BD). Ketamine is extensively metabolized. This study examined the relationship between ketamine metabolites and response, diagnosis, and psychotomimetic symptoms in MDD and BD patients. Methods Following a 40-minute ketamine infusion (.5 mg/kg), plasma samples were collected at 40, 80, 110, and 230 minutes and day 1 postinfusion in 67 patients currently experiencing a major depressive episode (MDD, n = 45; BD, n = 22). Concentrations of ketamine, norketamine (NK), dehydronorketamine (DHNK), six hydroxynorketamine metabolites (HNK), and hydroxyketamine (HK) were measured. Plasma concentrations were analyzed by diagnostic group and correlated with patients’ depressive, psychotic, and dissociative symptoms. The relationship between cytochrome P450 gene polymorphisms and metabolites, response, and diagnosis was also examined. Results Ketamine, NK, DHNK, four of six HNKs, and HK were present during the first 230 minutes postinfusion. Patients with BD had higher plasma concentrations of DHNK, (2S,6S;2R,6R)-HNK, (2S,6R;2R,6S)-HNK, and (2S,5S;2R,5R)-HNK than patients with MDD, who, in turn, had higher concentrations of (2S,6S;2R,6R)-HK. Higher (2S,5S;2R,5R)-HNK concentrations were associated with nonresponse to ketamine in BD patients. Dehydronorketamine, HNK4c, and HNK4f levels were significantly negatively correlated with psychotic and dissociative symptoms at 40 minutes. No relationship was found between cytochrome P450 genes and any of the parameters examined. Conclusions A diagnostic difference was observed in the metabolism and disposition of ketamine. Concentrations of (2S,5S;2R,5R)-HNK were related to nonresponse to ketamine in BD. Some hydroxylated metabolites of ketamine correlated with psychotic and dissociative symptoms.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • (R,S)‐ketamine is a phencyclidine derivative that was initially developed as an anaesthetic agent and which is currently being studied in the treatment of pain and depression. After administration, the drug is extensively N‐demethylated to (R,S)‐norketamine. The pharmacokinetics of ketamine and norketamine have been extensively studied in volunteers and patients after the administration of anaesthetic and sub‐anaesthetic doses. However, ketamine and norketamine are extensively transformed into a series of diastereomeric hydroxyketamines and hydroxynorketamines and (R,S)‐dehydronorketamine metabolites. The plasma kinetics of these metabolites have not been elucidated. WHAT THIS STUDY ADDS • The current study expands the characterization of the disposition kinetics of (R,S)‐ketamine and (R,S)‐norketamine and presents a population pharmacokinetic analysis of (R)‐ketamine, (S)‐ketamine, (R)‐norketamine, (S)‐norketamine, (R)‐dehydronorketamine, (S)‐ dehydronorketamine and (2S,6S;2R,6R)‐hydroxynorketamine and the serum concentration–time profiles of multiple ketamine metabolites observed in the plasma of patients after a single 40 min infusion of a sub‐anaesthetic dose of the drug. The data demonstrate that while norketamine is an initial metabolite, it is not the major circulating metabolite and suggest that the determination of the downstream metabolites of ketamine may play a role in the pharmacological effects of the drug. AIM To construct a population pharmacokinetic (popPK) model for ketamine (Ket), norketamine (norKet), dehydronorketamine (DHNK), hydroxynorketamine (2S,6S;2R,6R)‐HNK) and hydroxyketamine (HK) in patients with treatment‐resistant bipolar depression. METHOD Plasma samples were collected at 40, 80, 110, 230 min on day 1, 2 and 3 in nine patients following a 40 min infusion of (R,S)‐Ket (0.5 mg kg−1) and analyzed for Ket, norKet and DHNK enantiomers and (2S,6S;2R,6R)‐HNK, (2S,6S;2R,6R)‐HK and (2S,6R;2R,6S)‐HK. A compartmental popPK model was constructed that included all quantified analytes, and unknown parameters were estimated with an iterative two‐stage algorithm in ADAPT5. RESULTS Ket, norKet, DHNK and (2S,6S;2R,6R)‐HNK were present during the first 230 min post infusion and significant concentrations (>5 ng ml−1) were observed on day 1. Plasma concentrations of (2S,6S;2R,6R)‐HK and (2S,6R;2R,6S)‐HK were below the limit of quantification. The average (S) : (R) plasma concentrations for Ket and DHNK were <1.0 while no significant enantioselectivity was observed for norKet. There were large inter‐patient variations in terminal half‐lives and relative metabolite concentrations; at 230 min (R,S)‐DHNK was the major metabolite in four out of nine patients, (R,S)‐norKet in three out of nine patients and (2S,6S;2R,6R)‐HNK in two out of nine patients. The final PK model included three compartments for (R,S)‐Ket, two compartments for (R,S)‐norKet and single compartments for DHNK and HNK. All PK profiles were well described, and parameters for (R,S)‐Ket and (R,S)‐n...

The objective was to determine the cytochrome P450s (CYPs) responsible for the stereoselective and regiospecific hydroxylation of ketamine ((R,S)-Ket) to diastereomeric hydroxyketamines, (2S,6S;2R,6R)-HK (5a) and (2S,6R;2R,6S)-HK (5b) and norketamine ((R,S)-norKet) to hydroxynorketamines, (2S,6S;2R,6R)-HNK (4a), (2S,6R;2R,6S)-HNK (4b), (2S,5S;2R,5R)-HNK (4c), (2S,4S;2R,4R)-HNK (4d), (2S,4R;2R,4S)-HNK (4e), (2S,5R;2R,5S)-HNK (4f).The enantiomers of Ket and norKet were incubated with HLMs and expressed CYPs. Metabolites were identified and quantified using LC/MS/MS and apparent kinetic constants estimated using single-site Michaelis-Menten, Hill or substrate inhibition equation.5a was predominantly formed from (S)-Ket by CYP2A6 and N-demethylated to 4a by CYP2B6. 5b was formed from (R)- and (S)-Ket by CYP3A4/3A5 and N-demethylated to 4b by multiple enzymes. norKet incubation produced 4a, 4c and 4f and minor amounts of 4d and 4e. CYP2A6 and CYP2B6 were the major enzymes responsible for the formation of 4a, 4d and 4f, and CYP3A4/3A5 for the formation of 4e. The 4b metabolite was not detected in the norKet incubates.5a and 4b were detected in plasma samples from patients receiving (R,S)-Ket, indicating that 5a and 5b are significant Ket metabolites. Large variations in HNK concentrations were observed suggesting that pharmacogenetics and/or metabolic drug interactions may play a role in therapeutic response.

A parallel chiral/achiral LC-MS/MS assay has been developed and validated to measure the plasma and urine concentrations of the enantiomers of ketamine, (R)-and (S)-Ket, in Complex Regional Pain Syndrome (CRPS) patients receiving a 5-day continuous infusion of a subanesthetic dose of (R,S)-Ket. The method was also validated for the determination of the enantiomers of the Ket metabolites norketamine, (R)-and (S)-norKet and dehydronorketamine, (R)-and (S)-DHNK, as well as the diastereomeric metabolites hydroxynorketamine, (2S,6S)-/(2R, 6R)-HNK and two hydroxyketamines, (2S,6S)-HKet and (2S,6R)-Hket. In this method, (R,S)-Ket, (R,S)-norKet and (R,S)-DHNK and the diastereomeric hydroxyl-metabolites were separated and quantified using a C 18 stationary phase and the relative enantiomeric concentrations of (R,S)-Ket, (R,S)-norKet and (R,S)-DHNK were determined using an AGP-CSP. The analysis of the results of microsomal incubations of (R)-and (S)-Ket and a plasma and urine sample from a CRPS patient indicated the presence of 10 additional compounds and glucuronides. The data from the analysis of the patient sample also demonstrated that a series of HNK metabolites were the primary metabolites in plasma and (R)-and (S)-DHNK were the major metabolites found in urine. The results suggest that norKet is the initial, but not the primary, metabolite and that downstream norKet metabolites play a role in (R,S)-Ket-related pain relief in CRPS patients.

ObjectiveIdentify metabolic changes produced by dimethyl fumarate (DMF) treatment and link them to immunological effects.MethodsWe enrolled 18 MS patients and obtained blood prior to DMF and 6 months postinitiation. We also enrolled 18 healthy controls for comparison. We performed global metabolomics on plasma and used weighted correlation network analysis (WGCNA) to identify modules of correlated metabolites. We identified modules that changed with treatment, followed by targeted metabolomics to corroborate changes identified in global analyses. We correlated changes in metabolite modules and individual metabolites with changes in immunological parameters.ResultsWe identified alterations in lipid metabolism after DMF treatment – increases in two modules (phospholipids, lysophospholipids and plasmalogens) and reduction in one module (saturated and poly‐unsaturated fatty acids) eigen‐metabolite values (all P < 0.05). Change in the fatty acid module was greater in participants who developed lymphopenia and was strongly associated with both reduction in absolute lymphocyte counts (r = 0.65; P = 0.005) and change in CD8+ T cell subsets. We also noted significant correlation of change in lymphocyte counts with multiple fatty acid levels (measured by targeted or untargeted methods).InterpretationThis study demonstrates that DMF treatment alters lipid metabolism and that changes in fatty acid levels are related to DMF‐induced immunological changes.