Clinical pharmacokinetics of quetiapine: an atypical antipsychotic

Pharmacokinetic profiles of extended release quetiapine fumarate compared with quetiapine immediate release

This 10-day, single-center, open-label, randomized, crossover study compared pharmacokinetic profiles and tolerability of extended release quetiapine fumarate (quetiapine XR) with quetiapine immediate release (quetiapine IR) in patients with schizophrenia, schizoaffective disorder or bipolar disorder. After a 2-day lead-in period during which patients received quetiapine XR 300 mg once daily, patients were randomized to quetiapine IR 150 mg twice daily followed by quetiapine XR 300 mg once daily, or quetiapine XR 300 mg once daily followed by quetiapine IR 150 mg twice daily. Pharmacokinetic parameters were evaluated at the end of each 4-day treatment period at steady state. Vital signs, laboratory values, and adverse events (AEs) were recorded throughout the study. The least squares means (90% confidence interval) of the ratio of the area under the plasma concentration-time curve over a 24 h dosing interval (AUC ([0-24 h])) for quetiapine XR/IR was 1.04 (0.92-1.19) and within the pre-defined range set for equivalence (0.80-1.25). Maximum plasma concentration at steady state (C(max)) was approximately 13% lower for quetiapine XR than for quetiapine IR (495.3 versus 568.1 ng/mL), time to reach C(max) (t(max)) was 5 h versus 2 h and mean concentration at the end of 24 h dosing interval (C(min)) was 95.3 versus 96.5 ng/mL, respectively. No patients withdrew from the study owing to AEs and there were no serious AEs or deaths related to study medication. No unexpected AEs, changes in vital signs or laboratory values were observed. These findings suggest that modifying the formulation does not change the overall absorption or elimination of quetiapine, and support emerging clinical evidence for the use of quetiapine XR as a once daily treatment in patients initiating therapy or those established on quetiapine IR.

In silico methods for predicting metabolism and mass fragmentation applied to quetiapine in liquid chromatography/time-of-flight mass spectrometry urine drug screening

Current in silico tools were evaluated for their ability to predict metabolism and mass spectral fragmentation in the context of analytical toxicology practice. A metabolite prediction program (Lhasa Meteor), a metabolite detection program (Bruker MetaboliteDetect), and a fragmentation prediction program (ACD/MS Fragmenter) were used to assign phase I metabolites of the antipsychotic drug quetiapine in the liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) accurate mass data from ten autopsy urine samples. In the literature, the main metabolic routes of quetiapine have been reported to be sulfoxidation, oxidation to the corresponding carboxylic acid, N- and O-dealkylation and hydroxylation. Of the 14 metabolites predicted by Meteor, eight were detected by LC/TOFMS in the urine samples with use of MetaboliteDetect software and manual inspection. An additional five hydroxy derivatives were detected, but not predicted by Meteor. The fragment structures provided by ACD/MS Fragmenter software confirmed the identification of the metabolites. Mean mass accuracy and isotopic pattern match (SigmaFit) values for the fragments were 2.40 ppm (0.62 mDa) and 0.010, respectively. ACD/MS Fragmenter, in particular, allowed metabolites with identical molecular formulae to be differentiated without a need to access the respective reference standards or reference spectra. This was well exemplified with the hydroxy/sulfoxy metabolites of quetiapine and their N- and O-dealkylated forms. The procedure resulted in assigning 13 quetiapine metabolites in urine. The present approach is instrumental in developing an extensive database containing exact monoisotopic masses and verified retention times of drugs and their urinary metabolites for LC/TOFMS drug screening.

Metabolism of quetiapine by CYP3A4 and CYP3A5 in presence or absence of cytochrome B5

The antipsychotic drug quetiapine is extensively metabolized by CYP3A4, but little is known about the possible influence of the polymorphic enzyme CYP3A5. This in vitro study investigated the relative importance of CYP3A4 and CYP3A5 in the metabolism of quetiapine and compared the metabolic pattern by the two enzymes, in the presence or absence of cytochrome b(5). Intrinsic clearance (CL(int)) of quetiapine was determined by the substrate depletion approach in CYP3A4 and CYP3A5 insect cell microsomes with or without coexpressed cytochrome b(5). Formation of the metabolites quetiapine sulfoxide, N-desalkylquetiapine, O-desalkylquetiapine, and 7-hydroxyquetiapine by CYP3A4 and CYP3A5 were compared in the different microsomal preparations. CL(int) of quetiapine by CYP3A5 was less than 35% relative to CYP3A4. CL(int) was higher (3-fold) in CYP3A4 microsomes without cytochrome b(5) compared with CYP3A4 microsomes with coexpressed cytochrome b(5), whereas in CYP3A5 microsomes CL(int) was similar for both microsomal preparations. Metabolism of quetiapine by CYP3A5 revealed a different metabolic pattern compared with CYP3A4. The results indicated that O-desalkylquetiapine constituted a higher proportion of the formed metabolites by CYP3A5 compared with CYP3A4. In conclusion, the present study indicates that CYP3A5 is of minor importance for the overall metabolism of quetiapine, regardless of the presence of cytochrome b(5). However, a different metabolic pattern by CYP3A5 compared with CYP3A4 could possibly result in different pharmacological and/or toxicological effects of quetiapine in patients expressing CYP3A5.

Successful treatment of KIT D816V-positive, imatinib-resistant systemic mastocytosis with interferon-alpha

We describe a case of systemic mastocytosis associated with myelodysplastic syndrome. The bone marrow showed multifocal clusters of mast cells and myeloid dysplasia. Sequencing of the KIT DNA revealed a point mutation at codon 816 including a substitution of valine for aspartic acid (D816V). The patient's tumor did not respond to imatinib; however, interferon-alpha reduced the bone marrow mast cells and serum total tryptase. The patient remains alive at one year after the diagnosis without disease progression.

Pharmacokinetics and pharmacodynamics of quetiapine in a patient with a massive overdose

We present a case of massive overdose with the atypical antipsychotic quetiapine in a 34-year-old woman (body weight 65 kg). At admission, approximately 2 to 4 hours after ingestion of approximately 24 g of quetiapine, the patient was comatose (Glasgow Coma Scale score 5), requiring orotracheal intubation and transfer to the intensive care unit. Because of myoclonic jerks and generalized seizures, benzodiazepines were administered. In addition to transient mild hypotension after intubation, the main cardiovascular manifestation was sinus tachycardia. The QT interval was normal, and the QTc interval (Bazett's correction) was maximally prolonged to 620 ms. However, no malignant arrhythmias were observed. The patient recovered within 2 days but remained agitated and aggressive, for which she was transferred to the psychiatric clinic. The pharmacokinetics of quetiapine in such a large overdose could not be described by simple first-order kinetics. The initially observed rapid decline of the plasma concentrations of quetiapine could be simulated by first-order kinetics (half life = 4.1 hr) and can most probably be explained by rapid distribution into tissues. The final elimination of the drug from the body occurred after approximately 34 hours at much slower rate, most probably reflecting redistribution from tissues into blood and consecutive hepatic clearance of the drug.

New developments in the management of major depressive disorder and generalized anxiety disorder: role of quetiapine

Quetiapine has demonstrated efficacy in schizophrenia, bipolar disorder and in the treatment of specific symptom clusters such as agitation and sleep problems in mood disorders. In this review, randomized controlled studies demonstrating efficacy, safety and tolerability of quetiapine in major depressive disorder (MDD) and general anxiety disorder (GAD) are evaluated. The results show that quetiapine monotherapy and quetiapine augmentation of antidepressant treatment in MDD and GAD are efficacious for short-term and maintenance treatment at a dose range between 50 and 300 mg/day. Quetiapine appears to have a specific but overall mild side-effect profile, though, some adverse effects such as sedation and somnolence may lead to withdrawal from treatment in some patients. Overall, the available evidence suggests that there is a significant role for quetiapine in the treatment of MDD and GAD.

Quetiapine augmentation in depressed patients with partial response to antidepressants

OBJECTIVE

Clinical trials suggest between 30-50% of depressed patients have an inadequate outcome to antidepressant pharmacotherapy. Among the approaches to improve outcome has been augmentation with antipsychotic medications. We aim to investigate the efficacy and tolerability of augmentation with quetiapine in depressed patients with a partial response to antidepressants.

METHODS

Patients with a Major Depressive Disorder (DSMIV) who had partial/no response to a stable dose of an Selective Serotonin Reuptake Inhibitors (SSRI)/SNRI were recruited. All patients received add-on quetiapine (200-600 mg nocte) in a 6-week trial. Outcome measures (HAMD, MADRS) were assessed at screening, baseline, weeks 1, 2, 4 and 6. Extrapyramidal symptoms (EPSEs) were assessed at baseline, weeks 2, 4 and 6. A neuropsychological battery of tests was administered at baseline, weeks 3 and 6.

RESULTS

Nineteen patients entered the trial and 18 completed the trial per protocol. We report a rapid improvement in depression ratings over 6 weeks (p < 0.0005) and remission rates of 67% at week 1 and 94% at week 6. There was no evidence of EPSE and no worsening (and some improvement) of cognition.

CONCLUSION

This suggests clinical benefits of quetiapine augmentation of SSRI/SNRI antidepressants with no worsening, and possible improvements in cognition.

Pharmacokinetics and time-course of D(2) receptor occupancy induced by atypical antipsychotics in stabilized schizophrenic patients

The (123)I-IBZM SPECT measured D(2) receptor occupancy (D(2)RO) in chronically dosed, stabilized schizophrenic patients and its relationship with antipsychotic (AP) pharmacokinetics (PK) over time is still unclear. The aims of this study were: 1) To define the relationship between striatal D(2) receptor occupancy (D( 2)RO) and plasma concentration (C(P)) in stabilized schizophrenic patients on clinically relevant doses using (123)I-IBZM SPECT; 2) To investigate the time course of AP-induced D(2)RO and corresponding C(P). Forty-six schizophrenic patients on their clinically required doses of risperidone, olanzapine, clozapine or quetiapine were included. D( 2)RO and C(P) were measured over time following a sparse-sampling experimental design, and individual PK and D(2)RO-time profiles were estimated using a population approach. Observed striatal D(2)RO and C(P) ranges were 28-75% and 9.4-60.5 ng/mL for risperidone, 22-84% and 8.6-89.5 ng/mL for olanzapine, 5-53% and 41.6-818.2 ng/mL for clozapine and 0-64% and 37.9-719.6 ng/mL for quetiapine. A PK-D(2)RO relationship was found for the four APs. D(2)RO pattern over time was stable for risperidone, olanzapine and clozapine but fluctuating for quetiapine. Stabilized schizophrenic patients show a wide range of both D(2)RO and C(P) at clinically effective doses of the four AP, suggesting that clinical response to these AP may be maintained with D(2)RO below 65%. D(2)RO patterns over time differ between AP. These results should be considered for accurate interpretation of D(2)RO measurements, proper design of studies and optimization of drug regimens for patients on AP treatment.

Is quetiapine a drug of abuse? Reexamining the issue of addiction

BACKGROUND

The abuse and diversion of pharmacological agents with CNS mechanisms of action is an important concern from governmental, regulatory, public health and safety perspectives. In recent years, there have been an increased number of reports concerning the abuse and diversion of quetiapine in forensic population and in individuals with histories of substance abuse.

OBJECTIVE

To better understand this surging pattern the available body of evidence was critically examined.

METHODS

A literature search from January 1991 to July 2008 restricting papers to English and using PUBMED and PsychInfo was performed.

RESULTS

Nine papers were identified. The content of these papers is discussed in light of recent research on drug abuse.

Detection and identification of atypical quetiapine metabolite in urine

Quetiapine fumarate (Seroquel®) is an atypical antipsychotic dibenzothiazepine derivative. Due to its extensive hepatic metabolism and low level of unchanged excretion (< 1%) the routine toxicological drug-screening analyses of urine often leads to false negative results. In the present study, we report that a newly identified metabolite of quetiapine, N-desalkylquetiapine, can be used as an indicative marker of quetiapine-intake in urine using common GC-MS screening procedure. The structure of the mentioned metabolite was solved from the mass-spectrum obtained and the quetiapine presence was proved by consequent HPLC plasma analysis.

N-desalkylquetiapine, a potent norepinephrine reuptake inhibitor and partial 5-HT1A agonist, as a putative mediator of quetiapine's antidepressant activity

Quetiapine is an atypical antipsychotic drug that is also US FDA approved for treating bipolar depression, albeit by an unknown mechanism. To discover the potential mechanism for this apparently unique action, we screened quetiapine, its metabolite N-Desalkylquetiapine, and dibenzo[b,f][1,4]thiazepine-11(10-H)-one (DBTO) against a large panel of G-protein-coupled receptors, ion channels, and neurotransmitter transporters. DBTO was inactive at all tested molecular targets. N-Desalkylquetiapine had a high affinity (3.4 nM) for the histamine H(1) receptor and moderate affinities (10-100 nM) for the norepinephrine reuptake transporter (NET), the serotonin 5-HT(1A), 5-HT(1E), 5-HT(2A), 5-HT(2B), 5-HT(7) receptors, the alpha(1B)-adrenergic receptor, and the M(1), M(3), and M(5) muscarinic receptors. The compound had low affinities (100-1000 nM) for the 5-HT(1D), 5-HT(2C), 5-HT(3), 5-HT(5), 5-HT(6), alpha(1A), alpha(2A), alpha(2B), alpha(2C), H(2), M(2), M(4), and dopamine D(1), D(2), D(3), and D(4) receptors. N-Desalkylquetiapine potently inhibited human NE transporter with a K(i) of 12 nM, about 100-fold more potent than quetiapine itself. N-Desalkylquetiapine was also 10-fold more potent and more efficacious than quetiapine at the 5-HT(1A) receptor. N-Desalkylquetiapine was an antagonist at 5-HT(2A), 5-HT(2B), 5-HT(2C), alpha(1A), alpha(1D), alpha(2A), alpha(2C), H(1), M(1), M(3), and M(5) receptors. In the mouse tail suspension test, N-Desalkylquetiapine displayed potent antidepressant-like activity in VMAT2 heterozygous mice at doses as low as 0.1 mg/kg. These data strongly suggest that the antidepressant activity of quetiapine is mediated, at least in part, by its metabolite N-Desalkylquetiapine through NET inhibition and partial 5-HT(1A) agonism. Possible contributions of this metabolite to the side effects of quetiapine are discussed.

Functional pharmacogenetics/genomics of human cytochromes P450 involved in drug biotransformation

We investigated the elimination routes for the 200 drugs that are sold most often by prescription count in the United States. The majority (78%) of the hepatically cleared drugs were found to be subject to oxidative metabolism via cytochromes P450 of the families 1, 2 and 3, with major contributions from CYP3A4/5 (37% of drugs) followed by CYP2C9 (17%), CYP2D6 (15%), CYP2C19 (10%), CYP1A2 (9%), CYP2C8 (6%), and CYP2B6 (4%). Clinically well-established polymorphic CYPs (i.e., CYP2C9, CYP2C19, and CYP2D6) were involved in the metabolism of approximately half of those drugs, including (in particular) NSAIDs metabolized mainly by CYP2C9, proton-pump inhibitors metabolized by CYP2C19, and beta blockers and several antipsychotics and antidepressants metabolized by CYP2D6. In this review, we provide an up-to-date summary of the functional polymorphisms and aspects of the functional genomics of the major human drug-metabolizing cytochrome P450s, as well as their clinical significance.

Application and interpretation of hPXR screening data: Validation of reporter signal requirements for prediction of clinically relevant CYP3A4 inducers

A human pregnane X receptor (PXR) reporter-gene assay was established and validated using 19 therapeutic agents known to be clinical CYP3A4 inducers, 5 clinical non-inducers, and 6 known inducers in human hepatocytes. The extent of CYP3A4 induction (measured as RIF ratio in comparison to rifampicin) and EC50 was obtained from the dose-response curve. All of the clinical inducers (19/19) and human hepatocyte inducers (6/6) showed positive responses in the PXR assay. One out of five clinical non-inducers, pioglitazone, also showed a positive response. An additional series of 18 commonly used drugs with no reports of clinical induction was also evaluated as putative negative controls. Sixteen of these were negative (89%), whereas two of these, flutamide and haloperidol showed 16-fold (RIF ratio 0.79) and 10-fold (RIF ratio 0.48) maximal induction, respectively in the reporter-gene system. Flutamide and haloperidol were further demonstrated to cause CYP3A4 induction in human cryopreserved hepatocytes based on testosterone 6beta-hydroxylation activity. The induction potential index calculated based on the maximum RIF ratio, EC50, and in vivo maximum plasma concentration was used to predict the likelihood of CYP3A4 induction in humans. When the induction potential index is greater than 0.08, the compound is likely to cause induction in humans. A high-throughput screening strategy was developed based on the validation results at 1microM and 10microM for the same set of drugs. A RIF ratio of 0.4 was set as more practical screening cut-off to minimize the possibility of generating false positives. Thus, a tiered approach was implemented to use the human PXR reporter-gene assay from early lead optimization to late lead characterization in drug discovery.

Steady-state pharmacokinetic, safety, and tolerability profiles of quetiapine, norquetiapine, and other quetiapine metabolites in pediatric and adult patients with psychotic disorders

OBJECTIVE

The aim of this study was to investigate the steady-state pharmacokinetic, safety, and tolerability profiles of immediate-release quetiapine administered by similar dose-escalation regimens in pediatric and adult populations with psychotic or mood disorders.

METHODS

Pediatric patients aged 10-17 years were titrated to a quetiapine dose of 200 mg twice daily (b.i.d. on days 5-7, 400 mg b.i.d. on days 11-12, with a final 400-mg dose on day 13. In a separate trial, adult patients aged 18-45 years were titrated to a quetiapine dose of 200 mg b.i.d. on days 4-6, 400 mg b.i.d. on days 10-11, with a final 400-mg dose on day 12. Concentrations of quetiapine and three metabolites (quetiapine sulfoxide, 7-hydroxy quetiapine, and norquetiapine) were quantified in plasma and urine. Adverse events, vital signs, 12-lead electrocardiogram (ECG), and clinical laboratory tests were evaluated throughout the studies.

RESULTS

In both pediatric and adult populations, plasma concentrations of quetiapine and norquetiapine increased proportionately as the dose was escalated from 200 mg b.i.d. to 400 mg b.i.d. There were no age-related differences in the dose-normalized quetiapine plasma concentration-time curve (AUC(SS)) and maximum plasma concentration (C(SS,max)). Quetiapine was rapidly absorbed after 200-mg and 400-mg doses in pediatric patients [median t(max) (time to maximum plasma concentration) 1.5 hours, both doses] and adult patients (median t(max) 1.0 hour and 1.2 hours, respectively). The mean quetiapine t(1/2) (terminal elimination half-life) was approximately 6 hours for pediatric and 5 hours for adult patients. Norquetiapine displayed a similar median t(max) and a longer t(1/2) compared with quetiapine. Quetiapine was well tolerated, with no serious adverse events and no unexpected events reported.

CONCLUSION

Pediatric and adult populations demonstrated similar pharmacokinetic, safety, and tolerability profiles for quetiapine administered by dose escalation. The predictability in quetiapine concentration profiles for children aged 10 years to adults suggests that no dosage adjustment may be required when treating patients of these ages.

Drug-drug interactions with antipsychotics

Recognizing drug-drug interactions (DDIs) has become increasingly important as the country's demographics have aged, resulting in more complex medication regimens. Budnitz and colleagues highlighted the frequency of adverse drug reactions (ADRs) and the substantial morbidity that results. Their study estimated >700,000 cases of ADRs in emergency rooms (ER) in the United States between 2004 and 2005, and that ADRs accounted for 6.7% of ER visits for unintentional injuries that led to hospitalization. Moreover, medications that require monitoring accounted for 41.5% of all the ADR-related hospitalizations.

These data have tremendous implications for the field of psychiatry because many psychiatric drugs require therapeutic monitoring. The importance of DDIs is particularly relevant for the psychiatric population, where adverse effects not only cause short-term morbidity, but may lead to long-term treatment noncompliance. For many patients taking antipsychotics, adherence is the key to a successful outcome. Minimizing DDIs maximizes the chance that people will avoid unnecessary ADRs while achieving therapeutic drug levels.

A review of quetiapine in combination with antidepressant therapy in patients with depression

BACKGROUND

Atypical antipsychotics are increasingly used in the treatment of a broad spectrum of psychiatric disorders. There is evidence that in addition to treating the positive and negative symptoms of schizophrenia, as well as mania in bipolar disorder, these agents may have a potential role to play in the treatment of depressive disorders. In the following article we review the literature regarding the role of atypical antipsychotics, and specifically, quetiapine, in the treatment of major depressive disorder.

MATERIALS AND METHODS

In March 2007 the authors performed a Medline search (English-language) using the keywords quetiapine and depression, revealing a total of 47 articles published. We also looked for cross-references in the published articles, obtained data-on-file from AstraZeneca Pharmaceutical L.P., and included abstracts presented at conferences and recent meetings.

RESULTS

From our review we found that there is increasing literature supporting the efficacy of add-on quetiapine in the treatment of major depressive disorder.

CONCLUSION

There is a need, however, for further well-designed, adequately powered, randomized, controlled trials to confirm this finding, specifically in unipolar depression.

Spotlight on quetiapine in bipolar depression

Quetiapine (Seroquel) is the only atypical antipsychotic approved in the US for use as monotherapy in both bipolar mania and depression, offering potential compliance advantages. Monotherapy with oral quetiapine 300 mg/day is effective in the treatment of patients with bipolar I or II depression. Rapid and sustained improvements in depressive and anxiety symptoms are seen with quetiapine, as well as improvements in health-related quality of life. Quetiapine is generally well tolerated in bipolar depression and is not associated with an increased risk of treatment-emergent mania. Thus, despite the current lack of data from active comparator trials, quetiapine monotherapy should be considered a first-line option for the acute treatment of bipolar depression.

Open-label steady-state pharmacokinetic drug interaction study on co-administered quetiapine fumarate and divalproex sodium in patients with schizophrenia, schizoaffective disorder, or bipolar disorder

OBJECTIVE

To determine whether there is a pharmacokinetic drug interaction between quetiapine fumarate and divalproex sodium.

METHODS

The pharmacokinetics and short-term tolerability and safety of coadministered quetiapine and divalproex were examined in adults with schizophrenia/schizoaffective disorder (Cohort A) or bipolar disorder (Cohort B) in an open-label, parallel, 2-cohort drug-interaction study conducted at three centers in the United States. Cohort A was administered quetiapine (150 mg bid) prospectively for 13 days, with divalproex (500 mg bid) added on days 6-13. Cohort B was administered divalproex (500 mg bid) for 16 days, with quetiapine (150 mg bid) added on days 9-16. Quetiapine and valproic acid plasma concentration-time data over a 12-h steady-state dosing interval were used to determine C(max), T(max), C(min), area under the plasma concentration-time curve (AUC(tau)), and oral clearance (CL/F).

RESULTS

In Cohort A (n = 18), addition of divalproex did increase the C(max) of quetiapine by 17% but did not change AUC(tau). In Cohort B (n = 15), addition of quetiapine decreased both total valproic acid C(max) and AUC(tau) by 11%. No differences were observed in adverse events (AEs) with either quetiapine or divalproex monotherapy or their combination.

CONCLUSION

Combination therapy with quetiapine (150 mg bid) and divalproex (500 mg bid) resulted in small and statistically non-significant pharmacokinetic changes.

Quetiapine: a review of its use in the treatment of bipolar depression

Quetiapine (Seroquel) is the only atypical antipsychotic approved in the US for use as monotherapy in both bipolar mania and depression, offering potential compliance advantages. Monotherapy with oral quetiapine 300 mg/day is effective in the treatment of patients with bipolar I or II depression. Rapid and sustained improvements in depressive and anxiety symptoms are seen with quetiapine, as well as improvements in health-related quality of life (HR-QOL). Quetiapine is generally well tolerated in bipolar depression and is not associated with an increased risk of treatment-emergent mania. Thus, despite the current lack of data from active comparator trials, quetiapine monotherapy should be considered a first-line option for the acute treatment of bipolar depression.

Cigarette smoking and irinotecan treatment: pharmacokinetic interaction and effects on neutropenia

PURPOSE

Several constituents of cigarette smoke are known to interact with drug metabolizing enzymes and potentially affect treatment outcome with substrate drugs. The purpose of this study was to determine the effects of cigarette smoking on the pharmacokinetics and adverse effects of irinotecan.

PATIENTS AND METHODS

A total of 190 patients (49 smokers, 141 nonsmokers) treated with irinotecan (90-minute intravenous administration on a 3-week schedule) were evaluated for pharmacokinetics. Complete toxicity data were available in a subset of 134 patients receiving 350 mg/m2 or 600 mg flat-fixed dose irinotecan.

RESULTS

In smokers, the dose-normalized area under the plasma concentration-time curve of irinotecan was significantly lower (median, 28.7 v 33.9 ng x h/mL/mg; P = .001) compared with nonsmokers. In addition, smokers showed an almost 40% lower exposure to SN-38 (median, 0.54 v 0.87 ng x h/mL/mg; P < .001) and a higher relative extent of glucuronidation of SN-38 into SN-38G (median, 6.6 v 4.5; P = .006). Smokers experienced considerably less hematologic toxicity. In particular, the incidence of grade 3 to 4 neutropenia was 6% in smokers versus 38% in nonsmokers (odds ratio [OR], 0.10; 95% CI, 0.02 to 0.43; P < .001). There was no significant difference in incidence of delayed-onset diarrhea (6% v 15%; OR, 0.34; 95% CI, 0.07 to 1.57; P = .149).

CONCLUSION

This study indicates that smoking significantly lowers both the exposure to irinotecan and treatment-induced neutropenia, indicating a potential risk of treatment failure. Although the underlying mechanism is not entirely clear, modulation of CYP3A and uridine diphosphate glucuronosyltransferase isoform 1A1 may be part of the explanation. The data suggest that additional investigation is warranted to determine whether smokers are at increased risk for treatment failure.

Increased (R)-methadone plasma concentrations by quetiapine in cytochrome P450s and ABCB1 genotyped patients

Steady-state plasma concentrations of (R)- (ie, the active form), (S)-, and (R,S)-methadone were measured in 14 addict patients in methadone maintenance treatment, before and after introduction of quetiapine, administered at a mean dosage of 138 mg/d (SD, 87 mg/d; median, 125 mg/d; range, 50-300 mg/d) during a mean period of 30 days (SD, 8 days; median, 30 days; range, 20-48 days). Eleven patients were genotyped as being CYP2D6 extensive metabolizers (EMs) and 3 patients as poor metabolizers. Eleven patients had the ABCB1 3435 CT or CC genotypes, and 3 patients had the ABCB1 3435 TT genotype, the latter genotype being associated with lower P-glycoprotein activity. Quetiapine significantly increases (R)-methadone concentration-dose ratios in the whole group [increase for (R)-methadone: mean, +21%; SD, +28%; median, +13%; range, -23% to +85%; P = 0.026], but not for (S)-methadone (mean, +23%; SD, +43%; median, +6%; range, -30% to +115%; P = 0.12) or for (R,S)-methadone (mean, +21%; SD, +34%; median, +9%; range, -21% to +95%; P = 0.064). The mean increases of (R)-methadone concentration-dose ratios were of 7%, 21%, and 30% in the CYP2D6 poor metabolizers, heterozygous EMs, and homozygous EMs, respectively, whereas they were of 3%, 23%, and 33% in the subjects with the ABCB1 3435 TT, CT, and CC genotypes, respectively. Thus, quetiapine increases the plasma concentrations of (R)-methadone, possibly in part by an interaction with CYP2D6 and/or with the P-glycoprotein transporter system. No signs of overmedication caused by increased methadone plasma concentrations were noticed by the staff or reported by the patients.

An open-label study of quetiapine in anorexia nervosa

BACKGROUND

Atypical antipsychotics may be beneficial in treating the core psychopathology of anorexia nervosa (AN).

METHODS

An 8 week open-label study of quetiapine was conducted in eight severely ill DSM-IV AN patients consecutively admitted to a specialist eating disorders unit. Participants were assessed by EDE-12, MADRS, YBOCS, SAPS-delusions and CDR neuropsychological battery at baseline, 4 weeks and 8 weeks, and by weekly body mass index (BMI), CGI and extrapyramidal scores. Quetiapine doses ranged from 50 mg to 800 mg per day, according to efficacy and tolerability.

RESULTS

Seven participants completed 4 weeks and five participants completed 8 weeks. All participants had clinically significant levels of specific eating disorders psychopathology, and mild to moderately severe depressive symptomatology. Apart from initial mild sedation, no subjects experienced any significant adverse events. Over 4 weeks there was no significant difference in BMI, but a significant difference in the EDE-12 restraint score. There were significant differences on BMI and EDE-12 restraint subscale scores over 8 weeks.

CONCLUSIONS

A double-blind placebo controlled study is required to further evaluate the therapeutic utility of quetiapine in severely ill AN patients beyond multidisciplinary specialist intervention.

Validated HPLC-MS/MS method for determination of quetiapine in human plasma

A validated, highly sensitive and selective high-pressure liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the quantitative determination of quetiapine (QUE) in human Na2EDTA plasma with mass spectrometry (MS) detection. Clozapine (CLO) was employed as an internal standard. Samples were extracted using solid phase extraction (SPE). Oasis HLB cartridges and the concentration of quetiapine was determined by isocratic HPLC-MS/MS. The SRM mode was used for MS/MS detection. The method was validated over a concentration range of 1.0-382.2 ng/mL. Inter- and intra-day precision and accuracy of the proposed method were characterized by relative standard deviation (R.S.D.) and the percentage of deviation, respectively; both were lower than 8%. The developed method was employed in the pharmacokinetic study of quetiapine.

Pharmacokinetics of Quetiapine in Overdose and the Effect of Activated Charcoal

The aim of the study was to investigate the pharmacokinetics of quetiapine overdose and the effect of charcoal. The data set included 204 concentration-time points from 54 quetiapine overdose events (median dose 2,700 mg (300-24,000 mg)). Charcoal was administered 0.5-6 h after 19 overdoses. A fully Bayesian methodology for population pharmacokinetic analysis was used and data were modelled using WinBUGS. Uncertainty in the dose history was considered in model building by estimating dose amount and dose time within a possible range. Inclusion of informative priors stabilized the model and population parameter values could be estimated well. A one-compartment model with first-order input and first-order elimination described the data. The final model included uncertainty in dose time. The median and interquartile range of the half-life for individual patients was 6.6 h (4.9-8.4 h). Charcoal was estimated to reduce fraction absorbed by 35%. Co-ingested CYP3A4 inhibitors appeared to decrease clearance and CYP3A4 inducers increase clearance. Charcoal administration may be beneficial after quetiapine overdose.

Quetiapine in the treatment of schizophrenia and related disorders

Quetiapine was developed in 1985 by scientists at AstraZeneca (formerly Zeneca) Pharmaceuticals. It received official US Food and Drug Administration approval in September 1997 and approval in Germany in 2000. Since then, quetiapine has been used in the treatment of severe mental illness in approximately 70 countries including Canada, most Western European countries, and Japan. Quetiapine is a dibenzothiazepine derivative with a relatively broad receptor binding profile. It has major affinity to cerebral serotonergic (5HT(2A)), histaminergic (H1), and dopaminergic D(1) and D(2) receptors, moderate affinity to alpha(1)- und alpha(2)-adrenergic receptors, and minor affinity to muscarinergic M1 receptors; it demonstrates a substantial selectivity for the limbic system. This receptor occupancy profile with relatively higher affinity for the 5HT(2A) receptor compared with the D(2) receptor is in part responsible for the antipsychotic characteristics and low incidence of extrapyramidal side-effects of quetiapine. The efficacy of quetiapine in reducing positive and negative symptoms of schizophrenia has been proven in several clinical trials with placebo-controlled comparators. Quetiapine has also demonstrated robust efficacy for treatment of cognitive, anxious-depressive, and aggressive symptoms in schizophrenia. Long-term trials show sustained tolerability for a broad spectrum of symptoms. Quetiapine has also proven efficacy and tolerability in the treatment of moderate to severe manic episodes, and in the treatment of juveniles with oppositional-defiant or conduct disorders, and in the geriatric dementia population. Recent data indicate that quetiapine may also be effective in the treatment of bipolar depressive symptoms without increasing the risk of triggering manic episodes, and in borderline personality disorder. In comparison with other antipsychotics, quetiapine has a favorable side-effect profile. In clinical trials only small insignificant prolongations of the QT interval were observed. Weight-gain liabilities and new-onset metabolic side-effects occupy a middle-ground among newer antipsychotics. As a result of its good efficacy and tolerability profile quetiapine has become well established in the treatment of schizophrenia and manic episodes.

Metabolic drug interactions with newer antipsychotics: a comparative review

Newer antipsychotics introduced in clinical practice in recent years include clozapine, risperidone, olanzapine, quetiapine, sertindole, ziprasidone, aripiprazole and amisulpride. These agents are subject to drug-drug interactions with other psychotropic agents or with medications used in the treatment of concomitant physical illnesses. Most pharmacokinetic interactions with newer antipsychotics occur at the metabolic level and usually involve changes in the activity of the major drug-metabolizing enzymes involved in their biotransformation, i.e. the cytochrome P450 (CYP) monooxygenases and/or uridine diphosphate-glucuronosyltransferases (UGT). Clozapine is metabolized primarily by CYP1A2, with additional contribution by other CYP isoforms. Risperidone is metabolized primarily by CYP2D6 and, to a lesser extent, CYP3A4. Olanzapine undergoes both direct conjugation and CYP1A2-mediated oxidation. Quetiapine is metabolized by CYP3A4, while sertindole and aripiprazole are metabolized by CYP2D6 and CYP3A4. Ziprasidone pathways include aldehyde oxidase-mediated reduction and CYP3A4-mediated oxidation. Amisulpride is primarily excreted in the urine and undergoes relatively little metabolism. While novel antipsychotics are unlikely to interfere with the elimination of other drugs, co-administration of inhibitors or inducers of the major enzymes responsible for their metabolism may modify their plasma concentrations, leading to potentially significant effects. Most documented metabolic interactions involve antidepressant and anti-epileptic drugs. Of a particular clinical significance is the interaction between fluvoxamine, a potent CYP1A2 inhibitor, and clozapine. Differences in the interaction potential among the novel antipsychotics currently available may be predicted based on their metabolic pathways. The clinical relevance of these interactions should be interpreted in relation to the relative width of their therapeutic index. Avoidance of unnecessary polypharmacy, knowledge of the interaction profiles of individual agents, and careful individualization of dosage based on close evaluation of clinical response and, possibly, plasma drug concentrations are essential to prevent and minimize potentially adverse drug interactions in patients receiving newer antipsychotics.

Effect of Topiramate on Plasma Concentrations of Clozapine, Olanzapine, Risperidone, and Quetiapine in Patients With Psychotic Disorders

OBJECTIVES

To investigate the effect of topiramate on the steady-state plasma concentrations of the second-generation antipsychotics--clozapine, olanzapine, risperidone, and quetiapine--in patients with schizophrenia or bipolar disorder.

METHODS

Thirty-eight outpatients on long-term treatment with clozapine (250-500 mg/d, n = 10), olanzapine (10-20 mg/d, n = 12), risperidone (3-6 mg/d, n = 9), or quetiapine (200-600 mg/d, n = 7) received adjunctive topiramate, gradually titrated up to a final dosage of 200 mg/d for 6 weeks. Pharmacokinetic assessments were made at baseline and at the end of treatment weeks 4 and 8 at topiramate dosages of 100 and 200 mg/d, respectively.

RESULTS

Plasma concentrations of clozapine and its metabolite (norclozapine), olanzapine, risperidone and its metabolite (9-hydroxy-risperidone), and quetiapine were not significantly modified during concomitant administration of topiramate. Adjunctive topiramate therapy was well tolerated in all groups.

CONCLUSIONS

These findings indicate that topiramate, at the dosages recommended for use as a mood stabilizer, does not affect the plasma levels of the new antipsychotics-clozapine, olanzapine, risperidone, and quetiapine.

Efficacy and tolerability of quetiapine in cluster B personality disorder: an open-label study

Objective. The aim of this open-label 8-week study was to assess the effectiveness of quetiapine on aggressive behaviour and social dysfunctions in patients suffering from a cluster B personality disorder (DSM-IV). Methods. The visits were performed at baseline and at days 14, 28 and 56. After a standard titration schedule, the patients received a dose augmented or reduced dose, within a range from 50 to 400 mg/day during the visits, depending on efficacy and tolerance. Assessment of efficacy was based on the French version of the Social Disability and Aggression Scale SDAS (SDAS-21). Response was defined as a decrease of ≥50% reduction of the total scores compared to baseline. Tolerability was assessed with the CGI, UKU, EPS-scales. Results and conclusion. Eight of the 12 patients included received 200 mg/day quetiapine after titration (all patients: 50-400 mg/day). At week 8, five out of 12 patients were responders based on the SDAS-21 scores for the average expression of the symptoms, and six out of 12 on the basis of SDAS-21 scores for the peak expression. There was a significant correlation between weight change and total SDAS variation (Kendall's τb= -0.644; p=0.02). These findings should be reexamined in further studies.

Clinical Pharmacokinetics of Atypical Antipsychotics

In the past, the information about the dose-clinical effectiveness of typical antipsychotics was not complete and this led to the risk of extrapyramidal adverse effects. This, together with the intention of improving patients' quality of life and therapeutic compliance, resulted in the development of atypical or second-generation antipsychotics (SGAs). This review will concentrate on the pharmacokinetics and metabolism of clozapine, risperidone, olanzapine, quetiapine, amisulpride, ziprasidone, aripiprazole and sertindole, and will discuss the main aspects of their pharmacodynamics. In psychopharmacology, therapeutic drug monitoring studies have generally concentrated on controlling compliance and avoiding adverse effects by keeping long-term exposure to the minimal effective blood concentration. The rationale for using therapeutic drug monitoring in relation to SGAs is still a matter of debate, but there is growing evidence that it can improve efficacy, especially when patients do not respond to therapeutic doses or when they develop adverse effects. Here, we review the literature concerning the relationships between plasma concentrations of SGAs and clinical responses by dividing the studies on the basis of the length of their observation periods. Studies with clozapine evidenced a positive relationship between plasma concentrations and clinical response, with a threshold of 350-420 ng/mL associated with good clinical response. The usefulness of therapeutic drug monitoring is well established because high plasma concentrations of clozapine can increase the risk of epileptic seizures. Plasma clozapine concentrations seem to be influenced by many factors such as altered cytochrome P450 1A4 activity, age, sex and smoking. The pharmacological effects of risperidone depend on the sum of the plasma concentrations of risperidone and its 9-hydroxyrisperidone metabolite, so monitoring the plasma concentrations of the parent compound alone can lead to erroneous interpretations. Despite a large variability in plasma drug concentrations, the lack of studies using fixed dosages, and discrepancies in the results, it seems that monitoring the plasma concentrations of the active moiety may be useful. However, no therapeutic plasma concentration range for risperidone has yet been clearly established. A plasma threshold concentration for parkinsonian side effects has been found to be 74 ng/mL. Moreover, therapeutic drug monitoring may be particularly useful in the switch between the oral and the long-acting injectable form. The reviewed studies on olanzapine strongly indicate a relationship between clinical outcomes and plasma concentrations. Olanzapine therapeutic drug monitoring can be considered very useful in assessing therapeutic efficacy and controlling adverse events. A therapeutic range of 20-50 ng/mL has been found. There is little evidence in favour of the existence of a relationship between plasma quetiapine concentrations and clinical responses, and an optimal therapeutic range has not been identified. Positron emission tomography studies of receptor blockade indicated a discrepancy between the time course of receptor occupancy and plasma quetiapine concentrations. The value of quetiapine plasma concentration monitoring in clinical practice is still controversial. Preliminary data suggested that a therapeutic plasma amisulpride concentration of 367 ng/mL was associated with clinical improvement. A therapeutic range of 100-400 ng/mL is proposed from non-systematic clinical experience. There is no direct evidence concerning optimal plasma concentration ranges of ziprasidone, aripiprazole or sertindole.

Quetiapine augmentation in treatment-resistant depression: a naturalistic study

RATIONALE

Treatment-resistant depression (TRD) is a common clinical problem, often complicated with suicidal ideations and greater lifetime functional impairment, and represents a considerable challenge to management and treatment.

OBJECTIVE

The aim of a prospective, open-label, noncomparative, flexible-dosed 20-week study was to evaluate the effects of quetiapine, as an add-on therapy, in patients with TRD who were refractory to previous treatments.

METHOD

Eighteen patients with major depressive disorder (DSM-IV criteria) were treated for 20 weeks with quetiapine (mean dose 315+/-109 mg/day). Patients were evaluated at baseline, weekly from 1 to 9 weeks, and then after 12, 16, and 20 weeks of treatment, using Hamilton rating scale for depression-17 items (HAMD) scale.

RESULTS

Fourteen patients with TRD completed the 20-week open trial with quetiapine. The augmentation with quetiapine significantly reduced total scores and scores listed in the anxiety subscale on the HAMD, and these effects were observed after the fourth week of treatment, while the depressed mood scores were significantly reduced after the fifth week of treatment. Quetiapine add-on treatment significantly decreased the scores listed in the insomnia subscale on the HAMD subscale after the second week of treatment.

CONCLUSION

Our preliminary data indicate that quetiapine add-on therapy appears to have beneficial effects in the treatment of patients with TRD.

Quetiapine: efficacy, tolerability and safety in schizophrenia

Quetiapine, a dibenzothiazepine derivative, is an atypical antipsychotic, multireceptor antagonist that has a preclinical profile similar to clozapine. Randomized studies have demonstrated the efficacy of quetiapine relative to placebo in the treatment of acute relapse and the long-term management of schizophrenia. Quetiapine is generally well tolerated relative to other antipsychotic medications, although side effects include sedation, orthostatic hypotension, anticholinergic and metabolic side effects. The purpose of this article is to critically review the current literature on quetiapine with an emphasis on emergent themes and key findings in the use of this agent for the treatment of schizophrenia. There are also continued efforts to understand, predict and manage the side-effect risk with quetiapine.

Methods to evaluate biliary excretion of drugs in humans: an updated review

Determining the biliary clearance of drugs in humans is very challenging because bile is not readily accessible due to the anatomy of the hepatobiliary tract. The collection of bile usually is limited to postsurgical patients with underlying hepatobiliary disease. In healthy subjects, feces typically are used as a surrogate to quantify the amount of drug excreted via nonurinary pathways. Nevertheless, it is very important to characterize hepatobiliary elimination because this is a potential site of drug interactions that might result in significant alterations in systemic or hepatic exposure. In addition to the determination of in vivo biliary clearance values of drugs, the availability of in vitro models that can predict the extent of biliary excretion of drugs in humans may be a powerful tool in the preclinical stages of drug development. In this review, recent advances in the most commonly used in vivo methods to estimate biliary excretion of drugs in humans are outlined. Additionally, in vitro models that can be employed to investigate the molecular processes involved in biliary excretion are discussed to present an updated picture of the new tools and techniques that are available to study the complex processes involved in hepatic drug transport.

Psychopharmacology in pediatric critical care

Psychopharmacologic treatment in pediatric critical care requires a careful child or adolescent psychiatric evaluation, including a thorough review of the history of present illness or injury, any current or pre-existing psychiatric disorder, past history, and laboratory studies. Although there is limited evidence to guide psychopharmacologic practice in this setting, psychopharmacologic treatment is increasing in critical care, with known indications for treatment, benefits, and risks; initial dosing guidelines; and best practices. Treatment is guided by the knowledge bases in pediatric physiology, psycho-pharmacology, and treatment of critically ill adults. Pharmacologic considerations include pharmacokinetic and pharmcodynamic aspects of specific drugs and drug classes, in particular elimination half-life, developmental considerations, drug interactions, and adverse effects. Evaluation and management of pain is a key initial step, as pain may mimic psychiatric symptoms and its effective treatment can ameliorate them. Patient comfort and safety are primary objectives for children who are acutely ill and who will survive and for those who will not. Judicious use of psychopharmacolgic agents in pediatric critical care using the limited but growing evidence base and a clinical best practices collaborative approach can reduce anxiety,sadness, disorientation, and agitation; improve analgesia; and save lives of children who are suicidal or delirious. In addition to pain, other disorders or indications for psychopharmacologic treatment are affective disorders;PTSD; post-suicide attempt patients; disruptive behavior disorders (especially ADHD); and adjustment, developmental, and substance use disorders. Treating children who are critically ill with psychotropic drugs is an integral component of comprehensive pediatric critical care in relieving pain and delirium; reducing inattention or agitation or aggressive behavior;relieving acute stress, anxiety, or depression; and improving sleep and nutrition. In palliative care, psychopharmacology is integrated with psychologicapproaches to enhance children's comfort at the end of life. Defining how best to prevent the adverse consequences of suffering and stress in pediatric critical care is a goal for protocols and for new psychopharmacologic research [23,153].

Effectiveness, safety, and pharmacokinetics of quetiapine in aggressive children with conduct disorder

OBJECTIVE

To provide an initial description of the effectiveness and pharmacokinetics (PK) of quetiapine in aggressive children with conduct disorder (CD).

METHOD

This 8-week, open-label outpatient trial, enrolled patients ages 6 to 12 years with CD. Outcome measures included the Rating of Aggression Against People and/or Property Scale (RAAPPS), Nisonger Child Behavior Rating Form (NCBRF), and the Conners Parent Rating Scale (CPRS-48). Blood sampling for PK analyses occurred at the end of weeks 2 and 8.

RESULTS

Seventeen children (16 boys, mean age 8.9 years) were treated. The mean dose at week 8 was 4.4 mg/kg (SD = 1.1 mg/kg). Significant decreases in the baseline scores of the RAAPPS, and several subscales of the NCBRF and the CPRS were found by the end of the study (p <.05). No patients discontinued because of an adverse event. No patients experienced extrapyramidal side effects. Quetiapine disposition was linear over the dose range studied. The elimination half-life of the drug averaged 3.9 and 2.9 hours and total body clearance averaged 3.5 and 3.0 L/hr/kg after study weeks 2 and 8, respectively.

CONCLUSIONS

These preliminary data suggest that aggressive children with CD may benefit from quetiapine. The PK of quetiapine supports twice-daily dosing in children with CD.

Effects of cytochrome P450 3A modulators ketoconazole and carbamazepine on quetiapine pharmacokinetics

AIMS

To explore the potential for drug interactions on quetiapine pharmacokinetics using in vitro and in vivo assessments.

METHODS

The CYP enzymes responsible for quetiapine metabolite formation were assessed using recombinant expressed CYPs and CYP-selective inhibitors. P-glycoprotein (Pgp) transport was tested in MDCK cells expressing the human MDR1 gene. The effects of CYP3A4 inhibition were evaluated clinically in 12 healthy volunteers that received 25 mg quetiapine before and after 4 days of treatment with ketoconazole 200 mg daily. To assess CYP3A4 induction in vivo, 18 patients with psychiatric disorders were titrated to steady-state quetiapine levels (300 mg twice daily), then titrated to 600 mg daily carbamazepine for 2 weeks.

RESULTS

CYP3A4 was found to be responsible for formation of quetiapine sulfoxide and N- and O-desalkylquetiapine and not a Pgp substrate. In the clinical studies, ketoconazole increased mean quetiapine plasma C(max) by 3.35-fold, from 45 to 150 ng ml(-1) (mean C(max) ratio 90% CI 2.51, 4.47) and decreased its clearance (Cl/F) by 84%, from 138 to 22 l h(-1) (mean ratio 90% CI 0.13, 0.20). Carbamazepine decreased quetiapine plasma C(max) by 80%, from 1042 to 205 ng ml(-1) (mean C(max) ratio 90% CI 0.14, 0.28) and increased its clearance 7.5-fold, from 65 to 483 l h(-1) (mean ratio 90% CI 6.04, 9.28).

CONCLUSIONS

Cytochrome P450 3A4 is a primary enzyme responsible for the metabolic clearance of quetiapine. Quetiapine pharmacokinetics were affected by concomitant administration of ketoconazole and carbamazepine, and therefore other drugs and ingested natural products that strongly modulate the activity or expression of CYP3A4 would be predicted to change exposure to quetiapine.

The use of atypical antipsychotics beyond psychoses: efficacy of quetiapine in bipolar disorder

BACKGROUND AND RATIONALE

Atypical antpsychotics have been sucessfully used in the treatment of bipolar disorder (BD), either as adjunctive or as monotherapy. Quetiapine is an atypical antipsychotic extensively used in the treatment of psychotic disorders. It has serotonergic and dopaminergic activity and it appears to be selective for the mesolimbic and mesocortical dopamine system. The aim of this paper was to review the recent literature on the use of quetiapine in the treatment of BD.

METHODS

The literature databases currently available online were searched for papers on quetiapine and BD. Papers and reports published between January 1995 and June 2005 were selected and reviewed critically.

RESULTS

Augmentative low dose quetiapine was found to be effective in BD partially responsive to conventional mood-stabilizers. Manic and mixed episodes have been the best studied, and quetiapine was found to be effective either as monotherapy or as adjunctive therapy in both randomized clinical trials and open-label studies. Data on the use of quetiapine in bipolar depression showed a significant efficacy and high remission rates. Maintenance data suggested a role of quetiapine as a good alternative to classical mood stabilizers in reducing recurrence rates of BD. A few studies on the efficacy in rapid cycling BD have also been published.

CONCLUSIONS

Quetiapine is an effective agent for the short- and long-term treatment of BD. The mechanism of action of quetiapine as a mood stabilizer is still unknown. Some preliminary data suggest the involvement of glutamate pathways but further studies are needed to clarify this issue.

Quetiapine in Overdosage

Data on quetiapine overdosage are only sparsely available in the literature. This study provides additional data on the pharmacokinetics and clinical effects of intoxication with this atypical antipsychotic drug. The authors performed a retrospective analysis of all quetiapine intoxications reported to and screened by the toxicological laboratory of the Central Hospital Pharmacy The Hague between January 1999 and December 2003. Cases with known suggested amount of intake and medical outcome were included. From the patient's medical record and from the toxicological laboratory findings, patient demographic characteristics (gender, age), details of quetiapine intoxication (estimated time of ingestion, estimated amount of ingestion, and coingested drugs) and clinical parameters were obtained. Severity of intoxication was graded by the Poisoning Severity Score (PSS). Individual pharmacokinetic parameter values were calculated using a one-compartment open model and a Bayesian fitting procedure. Out of a total of 21 intoxications with quetiapine, 14 fulfilled the inclusion criteria. The ingested dose ranged from 1200 to 18,000 mg. The blood concentration ranged from 1.1 to 8.8 mg/L with a lag time of 1 to 26.2 hours between time of ingestion and blood sampling at the emergency ward. The most frequent findings were somnolence and tachycardia. The PSS was minor in 6 patients (43%), moderate in 5 patients (36%), and severe in 3 patients (21%). Severity of intoxication was not associated with a higher amount of quetiapine intake. The authors found no correlation between the serum concentration of quetiapine and the amount ingested. Elimination t(1/2) was not prolonged. It can be concluded that quetiapine intoxications appear to proceed mildly. Tachycardia and somnolence were the main clinical symptoms in our case series. No fatalities occurred. The severity of clinical symptoms was not associated with either a high serum concentration or the suggested amount ingested of quetiapine.

Quetiapine: an approach for the treatment of bipolar disorders

Quetiapine is one of the atypical antipsychotics that are formally approved by the US FDA for use in bipolar disorders. In recent Phase III clinical studies, it has provided satisfactory efficacy in the treatment of mania. In ongoing Phase III trials, its efficacy in depression is being investigated. Current data also support its efficacy in special conditions of bipolar disorders, such as rapid cycling and mixed states, the treatment of children and subjects suffering from comorbidities, which is a condition often seen in bipolar patients, and the reason for the combination of several agents. Quetiapine is well tolerated widely and provides minimal interaction with other treatments.

Influence of age, gender, body weight and valproate comedication on quetiapine plasma concentrations

Quetiapine is a second-generation antipsychotic with a favourable risk/benefit profile that is increasingly used in psychiatric patients. Similar to other antipsychotics, the efficacy and adverse effects of quetiapine depend much more on the actual plasma concentration of the active drug than on the prescribed dose. The present study investigated whether age, gender, body weight or certain comedications influence quetiapine plasma concentration by determining quetiapine plasma levels by tandem mass spectrometry in 94 (36 male and 58 female) patients aged 42.2 +/- 20.0 years. Older age was a significant predictor of a higher quetiapine plasma concentration, with a mean increase of weight-corrected concentration/dose ratio of 11% per 10 years of age (P = 0.003). In females, the concentration/dose (C/D) ratio was 35.4% higher than in males (adjusted mean 0.144 ng/ml/mg for males versus 0.195 ng/ml/mg for females, respectively; P = 0.035). However, after correction for weight, the gender difference in C/D ratio dropped to 22% and significance was lost (P = 0.133). Valproate comedication was associated with a 77% increase in quetiapine plasma levels (P = 0.016). In conclusion, older age, body weight and comedication with valproate have to be considered when prescribing quetiapine. Higher plasma levels in female patients need to be replicated in larger samples.

IN VITRO STUDIES ON QUETIAPINE METABOLISM USING THE SUBSTRATE DEPLETION APPROACH WITH FOCUS ON DRUG-DRUG INTERACTIONS

The metabolism of the atypical antipsychotic quetiapine was investigated by in vitro methods. Pharmacokinetic parameters were determined in human liver microsomes and recombinant cytochrome P450 measuring substrate depletion and product formation. The cytochrome P450 isozymes CYP3A4 and CYP2D6 displayed activity towards quetiapine. The isozyme CYP2D6 played a minor role in the metabolism of quetiapine as CYP3A4 contributed 89% to the overall metabolism. A Km value of 18 microM was determined by substrate depletion, suggesting linear kinetics under therapeutic conditions. Drugs known to inhibit CYP3A4, such as ketoconazole and nefazodone, displayed almost complete inhibition at low concentrations, whereas inhibitors of CYP2D6 do not seem to have a clinically relevant effect.

Interactions between Antiepileptic and Antipsychotic Drugs

Antiepileptic and antipsychotic drugs are often prescribed together. Interactions between the drugs may affect both efficacy and toxicity. This is a review of human clinical data on the interactions between the antiepileptic drugs carbamazepine, valproic acid (sodium valproate), vigabatrin, lamotrigine, gabapentin, topiramate, tiagabine, oxcarbazepine, levetiracetam, pregabalin, felbamate, zonisamide, phenobarbital and phenytoin with the antipsychotic drugs risperidone, olanzapine, quetiapine, clozapine, amisulpride, sulpiride, ziprasidone, aripiprazole, haloperidol and chlorpromazine; the limited information on interactions between antiepileptic drugs and zuclopenthixol, periciazine, fluphenazine, flupenthixol and pimozide is also presented. Many of the interactions depend on the induction or inhibition of the cytochrome P450 isoenzymes, but other important mechanisms involve the uridine diphosphate glucuronosyltransferase isoenzymes and protein binding. There is some evidence for the following effects. Carbamazepine decreases the plasma concentrations of both risperidone and its active metabolite. It also decreases concentrations of olanzapine, clozapine, ziprasidone, haloperidol, zuclopenthixol, flupenthixol and probably chlorpromazine and fluphenazine. Quetiapine increases the ratio of carbamazepine epoxide to carbamazepine and this may lead to toxicity. The data on valproic acid are conflicting; it may either increase or decrease clozapine concentrations, and it appears to decrease aripiprazole concentrations. Chlorpromazine possibly increases valproic acid concentrations. Lamotrigine possibly increases clozapine concentrations. Phenobarbital decreases clozapine, haloperidol and chlorpromazine concentrations. Phenytoin decreases quetiapine, clozapine, haloperidol and possibly chlorpromazine concentrations. There are major gaps in the data. In many cases there are no published clinical data on interactions that would be predicted on theoretical grounds.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.

Rapid titration versus conventional titration of quetiapine in the treatment of bipolar mania: a preliminary trial

The present trial was designed as a pilot study to re-examine how fast the dose of quetiapine in combination with mood stabilizers can be titrated upward in acutely ill patients with bipolar mania. Patients were assigned to either a rapid titration group (RTG) or a conventional titration group (CTG). Quetiapine was administered twice daily in a 3-day period in the RTG (200 mg/day on day 1; 400 mg/day on day 2; and 600 mg/day on day 3) and in a 5-day period in the CTG (50 mg/day on day 1; 100 mg/day on day 2; 200 mg/day on day 3; 300 mg/day on day 4; and 400 mg/day on day 5). The Young Mania Rating Scale (YMRS) and Clinical Global Impression-Severity (CGI-S) scores were assessed at days 1 (baseline), 3, 5, 7, 14 and 21. The Barnes Akathisia Rating Scale and Simpson-Angus Rating Scale (SARS) were assessed at days 1, 2, 3, 4, 5, 6, 7, 14 and 21. RTG and CTG showed significant improvement on the scores of YMRS and CGI-S during the study without group differences. Both treatments were well tolerated without clinically significant differences in tolerability measures. Treatment was not limited by adverse events in the two groups. This study demonstrates the potential benefit and tolerability of rapid titration of quetiapine in the treatment of acutely ill bipolar disorder. This preliminary study proposes that rapid titration of quetipaine in combination with a mood stabilizer for the treatment of bipolar mania is effective and tolerable in comparison with conventional titration. A controlled study with a larger cohort should be performed.

Quetiapine cross-reactivity with plasma tricyclic antidepressant immunoassays

BACKGROUND

Toxicology screens obtained on patients who have overdosed on drugs frequently include tricyclic antidepressants (TCAs) as part of the evaluation. Quetiapine is an antipsychotic agent with structural similarity to the TCAs.

OBJECTIVE

To determine whether quetiapine may cross-react with plasma TCA immunoassays in vitro using commonly available autoanalyzers.

METHODS

Quetiapine stock solution was added to 9 separate samples of pooled drug-free human plasma to produce concentrations ranging from 1 to 640 ng/mL that were verified by gas chromatography. No quetiapine metabolites were present. Each spiked plasma sample was tested in a blinded fashion using the Abbott Tricyclic Antidepressant TDx Assay on the TDxFLx autoanalyzer in 2 separate laboratories, the Syva Emit tox Serum Tricyclic Antidepressant Assay on the AU400 autoanalyzer and the S TAD Serum Tricyclic Antidepressant Screen on the ACA-Star 300 autoanalyzer. The TDx assay is quantitative, while Emit and S TAD are qualitative screening assays with a threshold of 300 ng/mL for TCA positivity. The outcome of interest was a positive TCA result.

RESULTS

The quantitative assay showed concentration-related TCA cross-reactivity beginning at quetiapine concentrations of 5 ng/mL. The 640-ng/mL spiked sample produced TCA results of 379 and 385 ng/mL in labs 1 and 2, respectively. The qualitative assays were screened as TCA positive at quetiapine concentrations of 160 and 320 ng/mL for the S TAD and Emit assays, respectively.

CONCLUSIONS

Quetiapine cross-reacts with quantitative and qualitative plasma TCA immunoassays in a concentration-dependent fashion. Therapeutic use or overdose of quetiapine may result in a false-positive TCA immunoassay result.

Pharmacokinetic dosage guidelines for elderly subjects

Ageing is associated with a decline in drug elimination; hence, using the same doses as in younger adults may result in higher plasma drug concentrations and toxicity. Two approaches are available for dose correction to account for decreased drug elimination. One procedure is based on the extrarenal elimination fraction (Q(0)) and the age-dependent changes in creatinine clearance; the other uses the decline in total drug clearance (CL). Mean values of Q(0) and CL in young and old people are reported for many drugs in the literature and are summarised in this article. Although the pharmacokinetic techniques for dose adjustment in the elderly are useful, they provide only an average dose correction and neglect age-dependent changes in drug bio-availability, plasma protein binding, the fate of active metabolites, and altered sensitivity to drugs. To account for pharmacodynamic changes in old age, clinical and/or biochemical targets should be defined as therapeutic goals. Drugs whose effects cannot be monitored in these terms should be avoided in elderly individuals.