Plasma Concentrations of Quetiapine, N-Desalkylquetiapine, O-Desalkylquetiapine, 7-Hydroxyquetiapine, and Quetiapine Sulfoxide in Relation to Quetiapine Dose, Formulation, and Other Factors

Pharmacokinetic interaction of quetiapine and lamotrigine - victim and perpetrator?

OBJECTIVE

We aimed to investigate the ambiguous findings of earlier research regarding the reduction of quetiapine plasma levels when combined with lamotrigine, most likely via UDP-glucuronosyltransferase induction by lamotrigine.

METHODS

One thousand one hundred and fifty samples, divided into four groups of patients receiving either quetiapine immediate- (IR) or extended-release (XR) without or in combination with lamotrigine were compared regarding absolute and dose-adjusted plasma concentrations. Furthermore, samples of intra-individual controls were analyzed.

RESULTS

Patients receiving quetiapine IR in combination with lamotrigine showed 31% lower plasma (p = 0.002) and 23% lower dose-adjusted plasma concentrations (p = 0.004) compared to those receiving IR monotherapy. The proportion of patients with quetiapine plasma concentrations below the lower limit of the therapeutic reference range was 50% and 30% in the combination group and in patients receiving monotherapy, respectively (p = 0.03). However, no significant differences regarding plasma concentration (p = 0.13) and dose-adjusted plasma concentration (p = 0.42) were observed in patients with combination vs. monotherapy with the XR formulation of quetiapine. In the intra-individual controls, no trends could be identified, possibly due to insufficient number of samples (p > 0.05).

CONCLUSIONS

The combination of quetiapine IR with lamotrigine is associated with significantly lower drug concentrations of quetiapine, potentially impacting quetiapine effectiveness. For quetiapine ER, a significant interaction is less likely.

Post-therapy plasma concentrations of quetiapine in Taiwanese patients

AIMS

Quetiapine is widely used to treat psychiatric disorders such as major depression, generalized anxiety disorder, dysthymic disorder, and insomnia other than schizophrenia and bipolar disorder. This study investigated the diagnostic distribution of quetiapine use in patients in a psychiatric hospital, the doses of quetiapine prescribed, and the plasma concentrations (Cps) of quetiapine and active metabolites.

METHODS

We enrolled 107 patients who had been prescribed quetiapine for at least 4 weeks. Diagnoses, demographics, and concomitant medications were recorded. Blood sampling was performed in the morning, approximately 12 h after the before-bed dose of quetiapine.

RESULTS

Diagnoses comprised schizophrenia (n = 25), bipolar disorder (n = 51), major depression (n = 15), dysthymic disorder (n = 9), and others (n = 7). The daily dose (DD) of quetiapine ranged from 25 to 800 (175.9 ± 184.4) mg, with the mean Cp being 105.6 ± 215.3 ng/ml, with a mean Cps/DD ratio of 0.58 ± 0.55 ng/ml/mg. There was a moderate positive linear correlation between the dose and Cps of quetiapine (r = 0.60), and the interpatient variation in Cps/DD ratio was up to 26-fold.

CONCLUSION

Quetiapine is used in various doses to treat many psychiatric disorders other than psychosis, and it is usually prescribed as a secondary antipsychotic for symptoms such as insomnia or agitation. A wide interpatient variation of the Cps/DD ratio was noticed. Patients of East Asian descent may exhibit a 50% to 100% increase in the Cps/DD ratio for quetiapine compared with patients of Western descent.

Racial/Ethnic Differences in the Pharmacokinetics of Antipsychotics: Focusing on East Asians

Empirical clinical studies have suggested that East Asian patients may require lower dosages of psychotropic drugs, such as antipsychotics, lithium, and antidepressants, than non-Asians. Both the pharmacokinetic and pharmacodynamic properties of a drug can affect the clinical response of an illness. The levels of antipsychotics used for the treatment of schizophrenia may affect patient clinical responses; several factors can affect these levels, including patient medication adherence, body weight (BW) or body mass index, smoking habits, and sex. The cytochrome P450 (CYP) system is a major factor affecting the blood levels of antipsychotics because many antipsychotics are metabolized by this system. There were notable genetic differences between people of different races. In this study, we determined the racial or ethnic differences in the metabolic patterns of some selected antipsychotics by reviewing therapeutic drug monitoring studies in East Asian populations. The plasma concentrations of haloperidol, clozapine, quetiapine, aripiprazole, and lurasidone, which are metabolized by specific CYP enzymes, were determined to be higher, under the same daily dose, in East Asian populations than in Western populations.

New insights into quetiapine metabolism using molecular networking

Metabolism is involved in both pharmacology and toxicology of most xenobiotics including drugs. Yet, visualization tools facilitating metabolism exploration are still underused, despite the availibility of pertinent bioinformatics solutions. Since molecular networking appears as a suitable tool to explore structurally related molecules, we aimed to investigate its interest in in vitro metabolism exploration. Quetiapine, a widely prescribed antipsychotic drug, undergoes well-described extensive metabolism, and is therefore an ideal candidate for such a proof of concept. Quetiapine was incubated in metabolically competent human liver cell models (HepaRG) for different times (0 h, 3 h, 8 h, 24 h) with or without cytochrom P450 (CYP) inhibitor (ketoconazole as CYP3A4/5 inhibitor and quinidine as CYP2D6 inhibitor), in order to study its metabolism kinetic and pathways. HepaRG culture supernatants were analyzed on an ultra-high performance liquid chromatography coupled with tandem mass spectrometry (LC-HRMS/MS). Molecular networking approach on LC-HRMS/MS data allowed to quickly visualize the quetiapine metabolism kinetics and determine the major metabolic pathways (CYP3A4/5 and/or CYP2D6) involved in metabolite formation. In addition, two unknown putative metabolites have been detected. In vitro metabolite findings were confirmed in blood sample from a patient treated with quetiapine. This is the first report using LC-HRMS/MS untargeted screening and molecular networking to explore in vitro drug metabolism. Our data provide new evidences of the interest of molecular networking in drug metabolism exploration and allow our in vitro model consistency assessment.

Norquetiapine blocks the human cardiac sodium channel Nav1.5 in a state-dependent manner

Quetiapine, an atypical antipsychotic drug, is used for the treatment of schizophrenia and acute mania. Although a previous report showed that quetiapine blocked hERG potassium current, quetiapine has been considered relatively safe in terms of cardiovascular side effects. In the present study, we used the whole-cell patch-clamp technique to investigate the effect that quetiapine and its major metabolite norquetiapine can exert on human cardiac sodium channels (hNa_v1.5). The half-maximal inhibitory concentrations of quetiapine and norquetiapine at a holding potential of -90 mV near the resting potential of cardiomyocytes were 30 and 6 μM, respectively. Norquetiapine as well as quetiapine was preferentially bound in the inactivated state of the hNa_v1.5 channel. Norquetiapine slowed the recovery from inactivation of hNa_v1.5 and consequently induced strong use-dependent inhibition. Our results indicate that norquetiapine blocks hNa_v1.5 current in concentration-, state- and use-dependent manners, suggesting that the blockade of hNa_v1.5 current by norquetiapine may shorten the cardiac action potential duration and reduce the risk of QT interval prolongation induced by the inhibition of hERG potassium currents.

Effects of Age, Drug Dose, and Sampling Time on Salivary Levels of Olanzapine, Quetiapine, and Their Metabolites

Although blood is the basic test material to monitor levels of antipsychotic drugs in a person’s system, saliva could serve as a more convenient test material. Therefore, the aim of this novel study was to determine the correlations between the salivary levels of olanzapine and quetiapine (and their metabolites: N-demethyl olanzapine and norquetiapine) and the patient’s sex and age, dose level, and the time of sampling. The study involved two groups of patients: 21 female patients starting treatment immediately after being admitted to the hospital and 36 male and female nursing home residents, long-time users of the studied drugs. Women had lower levels of the tested analytes than men. Quetiapine levels in the saliva of people starting the treatment showed a positive correlation with the age of the patients and a strong positive correlation with the dose level. The saliva levels of olanzapine showed a strong correlation with its metabolite in patients who had recently started treatment. Among long-time users of this drug, salivary levels differed significantly before and after administration. In conclusion, the results indicate that there is a possibility of using saliva as a material for monitoring quetiapine or olanzapine concentrations, especially in people starting treatment.

Degradation studies of quetiapine fumarate by liquid chromatography-diode array detection and tandem mass spectrometry methods

Quetiapine fumarate (QUE) is an antipsychotic agent with a chemical structure that is susceptible to degradation; therefore, it is important to study its stability using appropriate analytical tools. Knowledge of the stability profile of a drug is important because chemical degradation of its active component often results in a loss of potency, affecting its efficacy and safety. This current work reports degradation studies of QUE as drug substance, under different stress conditions such as oxidation, hydrolysis, heat, humidity and photolysis, by a stability-indicating LC method. The chemical stability was evaluated using a simple HPLC/diode array detection method, with a core-shell C₁₈ column under isocratic conditions, which allows the separation of all primary degradation products (DPs) in a short run time. QUE was mainly degraded under oxidative and hydrolytic conditions, with the formation of three and two DPs, respectively, which were identified by electrospray ionization-tandem mass spectrometry. The method was properly validated in terms of linearity, accuracy, precision, selectivity, robustness and quantitation limit. Commercial tablets containing 25 mg of QUE were quantified, with results obtained within the United States Pharmacopeia limits. The proposed method is suitable to assess the stability and perform routine analysis of QUE in pharmaceutical samples.

The straw man of prescribing in psychiatry

‘Drug-centred’ prescribing in psychiatry has been proposed as a new and better approach than the current ‘disease-centred’ alternative. It targets symptoms most important to the patient using the concept that psychotropics act indirectly by altering normal functioning. I contend that it is a straw man: psychiatrists already use ‘drug-centred’ prescribing, applying their knowledge of a drug's pharmacological profile and evidence base to treat each patient's symptoms, not their diagnostic classification. Furthermore, there is no compelling evidence that psychotropics act by altering ‘normal’ functioning: rather, they have diverse effects on different mental states.

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.

Impact of genetic variability in CYP2D6, CYP3A5, and ABCB1 on serum concentrations of quetiapine and N-desalkylquetiapine in psychiatric patients

BACKGROUND

To investigate the impact of genetic variability in CYP2D6, CYP3A5, and ABCB1 on steady-state serum concentrations of quetiapine and the active metabolite, N-desalkylquetiapine, in psychiatric patients.

METHODS

Measured serum concentrations of quetiapine and N-desalkylquetiapine from patients with biobanked DNA samples were included retrospectively from a routine therapeutic drug monitoring database. The impact of CYP2D6, CYP3A5, and ABCB1 (345C>T) genotypes on dose-adjusted serum concentrations (C/D ratios) of quetiapine and N-desalkylquetiapine was investigated by multivariate mixed model analysis.

RESULTS

In total, 289 patients with 633 serum measurements were included. In the multivariate analysis, mean C/D ratio of N-desalkylquetiapine was estimated to be 33% and 22% higher in inherent CYP2D6 poor metabolizers (P = 0.03) and heterozygous extensive metabolizers (P < 0.001), respectively, compared with inherent extensive metabolizers. The ABCB1 3435C>T polymorphism and CYP3A5 genotype had no significant influence on either of the substances in the present material.

CONCLUSIONS

Genetic variability in CYP2D6 contributes to the interindividual variability in steady-state serum concentrations of N-desalkylquetiapine. Although the metabolite exhibits relevant pharmacological activity, the quantitative effect of CYP2D6 genotype on serum concentration of N-desalkylquetiapine is probably of limited clinical relevance for quetiapine treatment.

Quetiapine extended-release (Seroquel-XR) versus amitriptyline monotherapy for treating patients with fibromyalgia: a 16-week, randomized, flexible-dose, open-label trial

RATIONALE

Previous open-label studies have suggested that quetiapine could be a valuable alternative for treating fibromyalgia.

OBJECTIVE

This study aims to compare the efficacy and tolerability of extended-release quetiapine with amitriptyline for treating fibromyalgia.

METHODS

This study was a randomized, open-label, flexible-dose, non-inferiority trial. Patients with fibromyalgia were randomized to receive quetiapine extended-release (XR) (N = 45) (50 to 300 mg daily) or amitriptyline (N = 45) (10 to 75 mg daily) for 16 weeks. The primary endpoint was the change from baseline to endpoint in the Fibromyalgia Impact Questionnaire (FIQ) total score; the non-inferiority threshold was established at 8 points. The secondary outcomes included sleep quality, anxiety, depression, and quality of life.

RESULTS

Twenty-two (49%) patients in the quetiapine group and 34 (76%) patients in the amitriptyline group completed the study. We found a reduction of 9.8 points in the total FIQ score at the endpoint for the quetiapine-treated patients compared to 13.9 points for the amitriptyline-treated patients, for a difference of 4.14 points (80% confidence interval (CI) -0.70 to 8.98). No significant differences were found between the quetiapine XR and amitriptyline groups for any of the secondary outcomes. The proportion of patients discontinuing treatment due to adverse events was higher in the quetiapine group (n = 14, 31.1%) than the amitriptyline group (n = 3, 6.6%).

CONCLUSIONS

Our results appear to indicate that quetiapine XR does not provide similar efficacy to amitriptyline for treating patients with fibromyalgia. Quetiapine XR had a worse tolerability than amitriptyline in this population, possibly due to a relatively high starting dose.

Plasma quetiapine in relation to prescribed dose and other factors: data from a therapeutic drug monitoring service, 2000-2011

OBJECTIVE

Suggested predose plasma quetiapine target ranges for effective therapy in schizophrenia lie between 50 and 500 µg/l. We aimed to examine data from a quetiapine therapeutic drug monitoring (TDM) service to assess the plasma quetiapine concentrations attained at specified doses in clinical practice.

METHOD

We studied TDM data from patients given immediate-release quetiapine in the period 2000-2011.

RESULTS

There were 946 samples from 487 patients (257 males, age at time of first sample, median [range] 34 [14-87] years, and 230 females, age at time of first sample, median [range] 38 [10-92] years). The plasma quetiapine concentration was <50 and <100 µg/l in 30% and 50% of samples, respectively (no quetiapine detected in 9% of samples). The relationship between dose and plasma quetiapine was poor. The mean (95% confidence interval [CI]) quetiapine dose was higher (t = 3.6, df = 446, p <0.01) in males versus females (641 [600-1240] and 548 [600-943] mg/day, respectively), although there was no difference in median dose (600 mg/day) or in the mean (95% CI) plasma quetiapine concentrations attained. Smoking habit had no discernible effect on plasma quetiapine concentration.

CONCLUSIONS

There was a poor relationship between dose and plasma quetiapine concentration in this study, as found by others. This is probably because of the short plasma half-life of the drug, at least in part. Nevertheless, quetiapine TDM can help assess adherence and measurement of quetiapine metabolites, notably N-desalkylquetiapine, as well as quetiapine itself may enhance the value of quetiapine TDM in future.

Therapeutic drug monitoring of common antipsychotics

The aim of this review is to provide information for interpreting outcome results from monitoring of antipsychotics in biological samples. A brief overview of the working mechanisms, pharmacological effects, drug interactions, and analytical methods of classical and atypical antipsychotics is given. Nineteen antipsychotics were selected based on their importance in the worldwide market as follows: amisulpride, aripiprazole, asenapine, bromperidol, clozapine, flupenthixol, haloperidol, iloperidone, lurasidone, olanzapine, paliperidone, perphenazine, pimozide, pipamperone, quetiapine, risperidone, sertindole, sulpiride, and zuclopenthixol. A straightforward relationship between administered dose, plasma or serum concentration, clinical outcome, or adverse effects is often lacking. Nowadays, focus lies on therapeutic drug monitoring and individualized therapy to find adequate treatment, to explain treatment failure or nonresponse, and to check patient compliance. However, extensive research in this field is still mandatory.