Effects of norquetiapine, the active metabolite of quetiapine, on cloned hERG potassium channels.

Quetiapine is an atypical antipsychotic drug that is widely used for the treatment of schizophrenia. It is mainly metabolized by a cytochrome P450 system in the liver. Norquetiapine is a major active metabolite in humans with a pharmacological profile that differs distinctly from that of quetiapine. We used the whole-cell patch-clamp technique to investigate the effects of norquetiapine on hERG channels that are stably expressed in HEK cells. Quetiapine and norquetiapine inhibited the hERG tail currents at -50mV in a concentration-dependent manner with IC50 values of 8.3 and 10.8µM, respectively, which suggested equal potency. The block of hERG currents by norquetiapine was voltage-dependent with a steep increase over a range of voltages for channel activation. However, at more depolarized potentials where the channels were fully activated, the block by norquetiapine was voltage-independent. The steady-state inactivation curve of the hERG currents was shifted to the hyperpolarizing direction in the presence of norquetiapine. Norquetiapine did not produce a use-dependent block. A fast application of norquetiapine inhibited the hERG current elicited by a 5s depolarizing pulse to +60mV, which fully inactivated the hERG currents, suggesting an inactivated-state block. During a repolarizing pulse wherein the hERG current was slowly deactivated, albeit remaining in an open state, a fast application of norquetiapine rapidly and reversibly inhibited the open state of the hERG current. Our results indicated that quetiapine and norquetiapine had equal potency in inhibiting hERG tail currents. Norquetiapine inhibited the hERG current by preferentially interacting with the open and/or inactivated states of the channels.

The preclinical discovery and development of quetiapine for the treatment of mania and depression.

INTRODUCTION: Bipolar disorder is a chronic disabling condition characterized by alternating manic and depressive episodes. Bipolar disorder has been associated with functional impairment, poor quality of life, morbidity and mortality. Despite its significant clinical, social and economic burden, treatment options for bipolar disorder are still limited. Several clinical trials have shown efficacy of the atypical antipsychotic quetiapine (QTP) in the treatment of this condition. However, the mechanisms underlying the antidepressant and anti-manic effects of QTP remain poorly understood. Areas covered: The article provides the emerging evidence from pre-clinical studies regarding the antidepressant and anti-manic mechanisms of action of QTP. In combination with its primary active metabolite norquetiapine, QTP modulates several neurotransmitter systems, including serotonin, dopamine, noradrenaline and histamine. QTP also seems to influence mediators of the immune system. Expert opinion: Pre-clinical studies have provided valuable information on the potential antidepressant mechanisms of action of QTP, but pre-clinical studies on QTP's anti-manic effects are still scarce. A major problem refers to the lack of valid experimental models for bipolar disorder. Additionally, immune and genetic based studies are largely descriptive. The role of the QTP metabolite norquetiapine in modulating non-neurotransmitter systems also needs to be further addressed.

Comparative Physicochemical and Pharmacokinetic Properties of Quetiapine and Its Active Metabolite Norquetiapine.

Quetiapine (QTP) is an atypical antipsychotic drug commonly used to treat several psychiatric disorders and is metabolized into the active metabolite norquetiapine (NQTP). This study was designed to evaluate and compare the physicochemical properties, metabolic stability, brain distribution, and pharmacokinetics of QTP and NQTP. Compared to QTP, NQTP had a higher pKa, solubility, and rat liver microsomal stability, optimal log D and similar log P values. For pharmacokinetic evaluation, QTP and NQTP were administered orally and intravenously to rats at various doses. The plasma QTP and NQTP concentrations in rats were determined by a fully-validated liquid-chromatography tandem mass spectrometry (LC-MS/MS). Over the investigated dosing range, both QTP and NQTP showed linear pharmacokinetics. Following oral administration of the same dose, the area under the concentration-time curve (AUC0-∞) and maximum serum concentration (Cmax) were larger after NQTP administration compared to QTP administration. In addition, NQTP had a greater absolute oral bioavailability compared to QTP (15.6% vs. 0.63%, respectively). The brain-to-plasma concentration ratio was greater after NQTP administration compared to the QTP and NQTP ratios after QTP administration. NQTP administration results in increased systemic exposure and brain distribution compared to QTP administration. Future studies are needed to evaluate the pharmacologic and toxicologic effects of increased NQTP exposures.

Reversible dimers of the atypical antipsychotic quetiapine inhibit p-glycoprotein-mediated efflux in vitro with increased binding affinity and in situ at the blood-brain barrier.

The multidrug resistance transporter P-glycoprotein (P-gp) is highly expressed in the capillary endothelial cells of the blood-brain barrier (BBB) where it functions to limit the brain penetration of many drugs, including antipsychotic agents used to treat schizophrenia. Therefore, in an effort to inhibit the transporter, we designed dimers of the antipsychotic drug and P-gp substrate quetiapine (QT), linked by variable length tethers. In P-gp overexpressing cells and in human brain capillary endothelial hCMEC/D3 cells, the dimer with the shortest tether length (QT2C2) (1) was the most potent inhibitor showing >80-fold better inhibition of P-gp-mediated transport than monomeric QT. The dimers, which are linked via ester moieties, are designed to revert to the therapeutic monomer once inside the target cells. We demonstrated that the addition of two sterically blocking methyl groups to the linker (QT2C2Me2, 8) increased the half-life of the molecule in plasma 10-fold as compared to the dimer lacking methyl groups (QT2C2, 1), while retaining inhibitory potency for P-gp transport and sensitivity to cellular esterases. Experiments with purified P-gp demonstrated that QT2C2 (1) and QT2C2Me2 (8) interacted with both the H- and R-binding sites of the transporter with binding affinities 20- to 30-fold higher than that of monomeric QT. Using isolated rat brain capillaries, QT2C2Me2 (8) was a more potent inhibitor of P-gp transport than QT. Lastly, we showed that QT2C2Me2 (8) increased the accumulation of the P-gp substrate verapamil in rat brain in situ three times more than QT. Together, these results indicate that the QT dimer QT2C2Me2 (8) strongly inhibited P-gp transport activity in human brain capillary endothelial cells, in rat brain capillaries, and at the BBB in an animal model.

Norepinephrine transporter occupancy in the human brain after oral administration of quetiapine XR.

Quetiapine, originally developed as an antipsychotic, demonstrates efficacy in clinical studies of schizophrenia, bipolar mania and depression, major depressive disorder and generalized anxiety disorder. This broad spectrum of efficacy was not predicted from the preclinical pharmacology of quetiapine. Binding studies in vitro show that quetiapine and its major active human metabolite, norquetiapine, have moderate to high affinity for dopamine D2 and serotonin 5-HT2A receptors, while norquetiapine alone has high affinity for the norepinephrine transporter (NET). This positron emission tomography (PET) study measured NET occupancy in human subjects treated with extended-release quetiapine (quetiapine XR) at doses relevant in the treatment of depression. PET measurements using the specific NET radioligand (S,S)-[(18)F]FMeNER-D2 were performed before and after quetiapine XR treatment at 150 and 300 mg/d for 6-8 d in nine healthy males (aged 21-33 yr). Regions of interest were defined for the thalamus, using the caudate as reference region. NET occupancy was calculated using a target:reference region ratio method. Plasma concentrations of quetiapine and norquetiapine were monitored during PET measurements. Following quetiapine XR treatment, the mean NET occupancy in the thalamus was 19 and 35%, respectively, at quetiapine XR doses of 150 and 300 mg/d. The estimated plasma concentration of norquetiapine corresponding to 50% NET occupancy was 161 ng/ml. This is the first demonstration of NET occupancy by an antipsychotic in the human brain. NET inhibition is accepted as a mechanism of antidepressant activity. NET occupancy may therefore contribute to the broad spectrum of efficacy of quetiapine.

Effect of atypical antipsychotics on antioxidant enzyme activities in human erythrocytes (in vitro study).

OBJECTIVE: This study was set out to examine the impact of atypical antipsychotic drugs: aripiprazole, clozapine, ziprasidone, olanzapine, quetiapine, sertindole and amisulpride on the activity of antioxidant defence enzymes in human erythrocytes in vitro. METHODS: Cu,Zn-superoxide dismutase (SOD1), catalase (CAT), selenium-dependent glutathione peroxidase and glutathione reductase activities were determined after drugs incubation with blood of 15 apparently healthy non-smoking male volunteers (ages 23-39) for 1 h at 37 °C. RESULTS: A statistically significant increase in SOD1 activity was found in samples incubated with aripiprazole (p < 0.01) and quetiapine (p < 0.05) compared with incubated control. SOD1 activity profile following native polyacrylamide gel electrophoresis indicates that aripiprazole and quetiapine protect enzyme activity from inhibition with hydrogen peroxide. Our results showed that sertindole decreases activity of CAT comparing with control non-treated erythrocytes. Moreover, in sertindole treated erythrocytes, negative correlation between SOD1 and glutathione peroxidase activities was found. Increased amount of hydrogen peroxide in such situation may leave erythrocytes and transform their role in circulation from anti-oxidative to pro-oxidative. CONCLUSIONS: Our results indicate that mechanism through sertindole could express its in vivo toxic effects and point toward possible (neuro)protective effects of aripiprazole and quetiapine.

Metabolism of the active metabolite of quetiapine, N-desalkylquetiapine in vitro.

The antipsychotic drug quetiapine has been approved for the treatment of unipolar and bipolar depression. The antidepressant activity is considered to be mediated by the active metabolite N-desalkylquetiapine, which is mainly formed by CYP3A4. Little is known about the subsequent elimination of this metabolite. Therefore, this study investigated the possible involvement of cytochrome P450 (P450) enzymes in the metabolism of N-desalkylquetiapine. Screening for and interpretation of metabolites were performed by incubating N-desalkylquetiapine in human liver microsomes (HLM) followed by liquid chromatography-tandem mass spectrometry. The possible involvement of P450 enzymes in N-desalkylquetiapine metabolism was evaluated by coincubation of selective P450 inhibitors in HLM and subsequent experiments with recombinant human P450 enzymes. In HLM experiments, three chromatographic peaks were interpreted as possible metabolites of N-desalkylquetiapine, namely, N-desalkylquetiapine sulfoxide, 7-hydroxy-N-desalkylquetiapine, and an unrecognized metabolite (denoted M3). Inhibition of CYP2D6 (by quinidine) reduced formation of 7-hydroxy-N-desalkylquetiapine by 81%, whereas the CYP3A4 inhibitor ketoconazole inhibited formation of N-desalkylquetiapine sulfoxide and M3 by 65 and 34%, respectively. Inhibitors of CYP1A2, CYP2C9, and CYP2C19 showed only limited changes in metabolite formation. In recombinant systems, 7-hydroxy-N-desalkylquetiapine was exclusively formed by CYP2D6, whereas N-desalkylquetiapine sulfoxide and M3 were formed by both CYP3A4 and CYP2D6. Overall, intrinsic clearance of N-desalkylquetiapine was 12-fold higher by recombinant CYP2D6 relative to CYP3A4. In conclusion, N-desalkylquetiapine is metabolized by both CYP2D6 and CYP3A4 in vitro with preference for the former enzyme. The pharmacologically active metabolite, 7-hydroxy-N-desalkylquetiapine, was exclusively formed by CYP2D6, whereas the two other metabolites were mainly formed by CYP3A4.

Potential role of a quetiapine metabolite in quetiapine-induced neutropenia and agranulocytosis.

Clozapine was the first of the atypical antipsychotics to be developed, but its use has been restricted because of toxicity issues, particularly the risk of potentially life-threatening drug-induced neutropenia and agranulocytosis, which occurs in about 1% of patients. Bioactivation of clozapine by peroxidases forms a reactive nitrenium ion, which covalently adducts to protein and leads to neutrophil toxicity. The current generation of clozapine-inspired atypical antipsychotics has reduced toxicity through improved potency/decreased dose or through structural modification to prevent peroxidase-catalyzed nitrenium ion formation. Through the substitution of sulfur for the bridging nitrogen found in clozapine, quetiapine does not directly form a nitrenium ion when incubated with myeloperoxidase/H(2)O(2). We present evidence that cytochrome P450 2D6 catalyzes the formation of 7-hydroxyquetiapine, which can be oxidized by human myeloperoxidase to form a reactive quinone-imine and a reactive radical, which may account for the continued, although reduced, neutrophil toxicity. In the presence of myeloperoxidase/H(2)O(2) and glutathione, covalent 7-hydroxyquetiapine-glutathione adducts were formed. Bioactivation of quetiapine was verified in vivo in rat where three 7-hydroxyquetiapine-mercaptate adducts and a 7-hydroxyquetiapine-glutathione adduct were detected from bile after oral dosing. The decreased incidence of agranulocytosis with quetiapine over clozapine is postulated to be due to the lower exposure of the toxic precursor, 7-hydroxyquetiapine versus clozapine, respectively.

Effect of quetiapine and norquetiapine on anxiety and depression in major psychoses using a pharmacokinetic approach: a prospective observational study.

BACKGROUND: Quetiapine apparently differs from other antipsychotic drugs in terms of its antidepressant activity and efficacy in bipolar depression. The mechanism of this activity is unknown although it may be mediated by its metabolite N-desalkylquetiapine (norquetiapine). OBJECTIVE: The aim of the study was to analyse the relationships between quetiapine and norquetiapine plasma concentrations and clinical improvement in depressive and anxious symptoms. METHODS: This was a prospective observational study. Recruited patients were evaluated during a clinical post-acute phase. Patients were recruited from patients hospitalized in the Psychiatric Department of Ospedale Maggiore Policlinico of Milan, Italy. After discharge they were followed-up as outpatients. The study involved 41 outpatients (23 males, 18 females; age >18 years) diagnosed as affected by schizophrenia (17 patients), borderline personality disorder (eight patients) or bipolar depression (16 patients) on the basis of the Diagnostic and Statistical Manual of Mental Disorders, fourth text revision (DSM-IV-TR) criteria. Patients were prescribed 50-800 mg of quetiapine (Seroquel®). Patients were evaluated after discharge from the psychiatric department (baseline, T0), after 15 days (T1) and after 3 months (T2) using the Brief Psychiatry Rating Scale (BPRS) with particular reference to the dimensions of depression (items 5, 9 and 13) and anxiety (items 1, 2 and 6). Plasma quetiapine and norquetiapine concentrations were determined by means of high-performance liquid chromatography at T2. RESULTS: There was a significant improvement in the mean BPRS total score, as well as in the dimensions of anxiety and depression. The bipolar patients only showed a significant curvilinear relationship described by a second-order polynomial model between the plasma norquetiapine/quetiapine concentration ratio and the improvement in depression at T2. There was a significant negative linear correlation between the norquetiapine/quetiapine ratio and anxiety in all of the patients. CONCLUSION: The results of this study confirm the efficacy of quetiapine on both anxious and depressive symptoms. Norquetiapine has a specific effect on anxiety and depressive symptoms, showing a correlation between plasma concentrations and clinical efficacy only in patients with bipolar depression.

Measurement of quetiapine and four quetiapine metabolites in human plasma by LC-MS/MS.

There is interest in monitoring plasma concentrations of N-desalkylquetiapine in relation to antidepressant effect. A simple LC-MS/MS method for quetiapine and four metabolites in human plasma (50 µL) has been developed to measure concentrations of these compounds attained during therapy. Analytes and internal standard (quetiapine-d8) were extracted into butyl acetate-butanol (10:1, v/v) and a portion of the extract analysed by LC-MS/MS (100 × 2.1 mm i.d. Waters Spherisorb S5SCX; eluent: 50 mmol/L methanolic ammonium acetate, pH* 6.0; flow-rate 0.5 mL/min; positive ion APCI-SRM, two transitions per analyte). Assay calibration (human plasma calibrators) was linear across the ranges studied (quetiapine and N-desalkylquetiapine 5-800, quetiapine sulfoxide 100-15,000, others 2-100 µg/L). Assay validation was as per FDA guidelines. Quetiapine sulfone was found to be unstable and to degrade to quetiapine sulfoxide. In 47 plasma samples from patients prescribed quetiapine (prescribed dose 200-950 mg/day), the (median, range) concentrations found (µg/L) were: quetiapine 83 (7-748), N-desalkylquetiapine, 127 (7-329), O-desalkylquetiapine 12 (2-37), 7-hydroxyquetiapine 3 (<1-48), and quetiapine sulfoxide 3,379 (343-21,704). The analyte concentrations found were comparable to those reported by others except that the concentrations of the sulfoxide were markedly higher. The reason for this discrepancy in unclear.

A randomized, double-blind study of once-daily extended release quetiapine fumarate (quetiapine XR) monotherapy in patients with generalized anxiety disorder.

This study evaluated once-daily, extended-release quetiapine fumarate (quetiapine XR) monotherapy in generalized anxiety disorder (GAD). This was a 10-week (8-week active treatment/2-week posttreatment drug-discontinuation/tapering phase), double-blind, randomized, placebo-controlled study (D1448C00009). Primary end point was change from randomization at week 8 in Hamilton Anxiety Rating Scale (HAM-A) total score. Overall, 951 patients with GAD were randomized (quetiapine XR: 50 mg/d, n = 234; 150 mg/d, n = 241; 300 mg/d, n = 241; placebo, n = 235). At week 8, HAM-A total scores significantly (P < 0.001) improved versus placebo (-11.10) with quetiapine XR 50 mg/d (-13.31) and 150 mg/d (-13.54), but not 300 mg/d (-11.87; P = 0.240). At week 1, HAM-A total scores significantly improved versus placebo (-5.94) with quetiapine XR 50 mg/d (-7.47; P < 0.01), 150 mg/d (-8.19; P < 0.001), and 300 mg/d (-7.23; P < 0.01). Versus placebo at week 8, quetiapine XR 50 and 150 mg/d significantly improved HAM-A psychic (P < 0.01 and P < 0.001, respectively) and somatic (P < 0.001; P < 0.01, respectively) cluster scores, HAM-A response (≥ 50% total score reduction; P < 0.05), and Clinical Global Impression-Improvement categorical changes (P < 0.05). For quetiapine XR 150 mg/d, significant (P < 0.05) improvements were seen for HAM-A remission (total score, ≤ 7) and Clinical Global Impression-Severity of Illness scores. For quetiapine XR 300 mg/d, improvements in these secondary variables were not significantly different versus placebo. Pittsburgh Sleep Quality Index global scores improved with all 3 doses (quetiapine: XR 50 mg/d, -4.07 [P < 0.05]; 150 mg/d, -4.38 [P < 0.05]; 300 mg/d, -3.97 [P < 0.05], versus -3.31 with placebo). Adverse events (>10% with quetiapine XR) were dry mouth, somnolence, sedation, dizziness, headache, and fatigue. Quetiapine XR (50/150 mg/d) monotherapy was effective at week 8 in patients with GAD; symptom improvement was seen at week 1 for all doses (50/150/300 mg/d). Safety and tolerability were consistent with the known profile of quetiapine.

Comparison of D2 dopamine receptor occupancy after oral administration of quetiapine fumarate immediate-release and extended-release formulations in healthy subjects.

Quetiapine is an established drug for treatment of schizophrenia, bipolar disorder, and major depressive disorder. While initially manufactured as an immediate-release (IR) formulation, an extended-release (XR) formulation has recently been introduced. Pharmacokinetic studies show that quetiapine XR provides a lower peak and more stable plasma concentration than the IR formulation. This study investigated if the pharmacokinetic differences translate into different time curves for central D2 dopamine receptor occupancy. Eleven control subjects were examined with positron emission tomography (PET) and the radioligand [11C]raclopride. Eight subjects underwent all of the scheduled PET measurements. After baseline examination, quetiapine XR was administered once-daily for 8 d titrated to 300 mg/d on days 5-8, followed by 300 mg/d quetiapine IR on days 9-12. PET measurements were repeated after the last doses of quetiapine XR and IR at predicted times of peak and trough plasma concentrations. Striatal D2 receptor occupancy was calculated using the simplified reference tissue model. Peak D2 receptor occupancy was significantly higher with quetiapine IR than XR in all subjects (50 ± 4% and 32 ± 11%, respectively), consistent with lower peak plasma concentrations for the XR formulation. Trough D2 receptor occupancy was similarly low for both formulations (IR 7 ± 7%, XR 8 ± 6%). The lower peak receptor occupancy associated with quetiapine XR may explain observed pharmacodynamic differences between the formulations. Assuming that our findings in control subjects are valid for patients with schizophrenia, the study supports the view that quetiapine, like the prototype atypical antipsychotic clozapine, may show antipsychotic effect at lower D2 receptor occupancy than typical antipsychotics.

Pharmacokinetic variability of quetiapine and the active metabolite N-desalkylquetiapine in psychiatric patients.

BACKGROUND: Quetiapine is an atypical antipsychotic drug that was recently also approved for the treatment of uni- and bipolar depression. The antidepressive response is considered to be mediated by the metabolite N-desalkylquetiapine, and the aim of this study was to assess the interindividual pharmacokinetic variability of quetiapine and N-desalkylquetiapine in psychiatric patients based on therapeutic drug monitoring samples. METHODS: Serum measurements of quetiapine and N-desalkylquetiapine performed between October 2007 and July 2008 were retrospectively included from a routine therapeutic drug monitoring database. Pharmacokinetic variability was expressed as the 5-95 percentile range in dose-adjusted serum concentrations (C/D ratios). The impact of age (65 years or older), gender, and sampling time on the C/D ratios was studied by linear mixed model analysis. Samples from patients comedicated with CYP3A4 inducers or inhibitors were examined separately. RESULTS: In total, 927 serum samples from 601 patients were included (all using quetiapine immediate-release tablets). The 5-95 percentiles of the C/D ratio ranged 15-fold (0.14-2.1 nmol/L/mg) for quetiapine and fivefold (0.44-2.1 nmol/L/mg) for N-desalkylquetiapine. Elderly (65 years or older) obtained 1.5- and 1.2-fold higher C/D ratios of quetiapine (P = 0.002) and N-desalkylquetiapine (P = 0.03) compared with younger patients, respectively. Sampling time was also found to significantly affect the C/D ratios of quetiapine (P = 0.001), whereas gender was not a significant variable (P > 0.13). In three patients treated with potent CYP3A4 inducers, the observed C/D ratios of quetiapine and N-desalkylquetiapine were 77% and 11% lower than the mean C/D ratio in the study population, respectively. CONCLUSION: The pharmacokinetic variability was greater for quetiapine compared with N-desalkylquetiapine. Age 65 years or older and comedication with CYP3A4 inducers affected the serum levels of both agents, but the relative impact was greater on quetiapine.

Interaction of clozapine and its nitrenium ion with rat D2 dopamine receptors: in vitro binding and computational study.

The interaction of diazepine analogues like clozapine or olanzapine with D2 receptor was greatly affected by a mixture of HRP/H(2)O(2) known to induce the formation of nitrenium ion. Unlike diazepine derivatives, the oxidative mixture had low impact on the affinity of oxa- and thiazepine derivatives such as loxapine, clothiapine or JL13 for the D2 receptor. Molecular docking simulations revealed a huge difference between the mode of interaction of clozapine nitrenium ion and the parent drug. Electronic and geometric changes of the tricyclic ring system caused by the oxidation appeared to prevent the compound finding the correct binding mode and could therefore explain the difference observed in binding affinities.

Sensorimotor gating and habituation in antipsychotic-naive, first-episode schizophrenia patients before and after 6 months' treatment with quetiapine.

Impaired prepulse inhibition of the startle reflex (PPI) in schizophrenia has been replicated in many studies. However, previous results may have been influenced by course of illness, and antipsychotic medication. Studies on antipsychotic-naive, first-episode schizophrenia patients are lacking, since these patients are so difficult to recruit. Furthermore, longitudinal studies are few, and their results are inconsistent: some results indicating a reduction of PPI deficits by treatment with atypical antipsychotics, while others do not. This study reports on PPI, habituation and sensitization of the human startle reflex in a large group of antipsychotic-naive, first-episode schizophrenia patients, and the effect of subsequent treatment with quetiapine. Thirty-four antipsychotic-naive, first-episode schizophrenia patients (24 males, 10 females), and age- and gender-matched healthy controls were tested in a psychophysiological test battery at baseline and again after 6 months. During this period, the patients were treated with quetiapine, while the controls received no treatment. Sixteen patients completed the study. At baseline, male patients showed significantly lower PPI than controls. Treatment with quetiapine for 6 months increased male PPI to a level where it was no longer statistically different from the controls. The much smaller group of females did not show PPI deficits at baseline. In addition, compared to controls, patients appeared highly aroused and showed a strong yet non-significant trend for reduced sensitization at baseline, but not at follow-up. Patients and controls showed similar levels of habituation, both at baseline, and at follow-up. These findings indicate that PPI deficits are already present from the earliest stage of clinical onset of schizophrenia, before the patients have received any antipsychotic treatment. In addition, following 6 months' treatment with quetiapine these PPI deficits were normalized. Furthermore, the results suggest that schizophrenia patients in the antipsychotic-naive state show reduced levels of sensitization, yet normal levels of habituation.

Dopamine D2/3 receptor occupancy by quetiapine in striatal and extrastriatal areas.

Quetiapine is next to clozapine an antipsychotic agent that exerts hardly any extrapyramidal side-effects at clinical efficacious doses. Some previous receptor occupancy studies reported preferential extrastriatal D2/3 receptor (D2/3R)-binding properties of second-generation antipsychotics and suggested this as possible reason for improved tolerability. This positron emission tomography (PET) investigation was designed to compare the occupancy of dopamine D2/3Rs by quetiapine in striatal and extrastriatal brain regions. Therefore, a cohort of 16 quetiapine-treated psychotic patients underwent an [18F]fallypride (FP) PET scan. Due to the high affinity of FP and its comparatively long half-life, striatal and extrastriatal binding potentials could be determined in one single scan. Receptor occupancy was calculated as percent reduction in binding potential relative to age-matched medication-free patients suffering from schizophrenia. Quetiapine occupied 44+/-18% in the temporal cortex and 26+/-17% in the putamen, a difference significant at the level of p=0.005 (Student's t test). Quetiapine showed a mean occupancy of 36+/-16% and in the thalamus. In the caudate nucleus there was an occupancy of 29+/-16% (p=0.0072). Individual occupancy levels did not exceed 59% in any of the striatal volumes of interest. The time-interval between scan and last drug ingestion did not influence the relationship between plasma concentration and central D2/3R occupancy. Taken together, quetiapine shows preferential extrastriatal binding at D2/3Rs; the extent of this difference is comparable to that previously described for clozapine. Both antipsychotics show very low affinity for D2/3Rs.

General unknown screening procedure for the characterization of human drug metabolites in forensic toxicology: applications and constraints.

LC coupled to single (LC-MS) and tandem (LC-MS/MS) mass spectrometry is recognized as the most powerful analytical tools for metabolic studies in drug discovery. In this article, we describe five cases illustrating the utility of screening xenobiotic metabolites in routine analysis of forensic samples using LC-MS/MS. Analyses were performed using a previously published LC-MS/MS general unknown screening (GUS) procedure developed using a hybrid linear IT-tandem mass spectrometer. In each of the cases presented, the presence of metabolites of xenobiotics was suspected after analyzing urine samples. In two cases, the parent drug was also detected and the metabolites were merely useful to confirm drug intake, but in three other cases, metabolite detection was of actual forensic interest. The presented results indicate that: (i) the GUS procedure developed is useful to detect a large variety of drug metabolites, which would have been hardly detected using targeted methods in the context of clinical or forensic toxicology; (ii) metabolite structure can generally be inferred from their "enhanced" product ion scan spectra; and (iii) structure confirmation can be achieved through in vitro metabolic experiments or through the analysis of urine samples from individuals taking the parent drug.

Metabolic consequences of using low-dose quetiapine for insomnia in psychiatric patients.

Quetiapine is frequently prescribed for insomnia that is comorbid with psychiatric disorders, but there has been no documentation of metabolic adverse effects associated with this practice. The objective of this study was to document changes in weight, body mass index, and waist circumference that occurred when low-dose quetiapine was used at bedtime for insomnia. The study was a retrospective chart review conducted at a community mental health center. Patients were non-elderly (19-65 years old) psychiatric patients who received quetiapine at < or =200 mg at bedtime for the explicit indication of insomnia. Forty-three patients were included in the study. Weight and BMI increased by an average of 4.9 lb. (P = 0.037) and 0.8 points (P = 0.048), respectively. Males experienced statistically significant increases in weight and BMI, and Caucasians experienced a statistically significant increase in BMI. There were no significant differences between baseline and endpoint metabolic parameters when examined by baseline BMI, age category, psychiatric diagnosis, or concomitant psychotropic medication. Despite the low doses typically used when quetiapine is prescribed for insomnia, metabolic adverse effects can occur and should be considered in the overall benefit to risk analysis.