MDR-1 genotypes and quetiapine pharmacokinetics in healthy volunteers

BACKGROUND

P-glycoprotein is an efflux transporter encoded by the multidrug-resistance MDR-1 gene, which influences the absorption and excretion of a variety of drugs. The relation between quetiapine pharmacokinetics and MDR-1 genetic polymorphisms remains controversial. Therefore, the aim of the present study was to analyze the association between quetiapine plasma concentrations and MDR-1 genetic polymorphisms in a bioequivalence trial.

METHODS

Quetiapine bioequivalence was studied in 24 unrelated healthy Caucasian adults with an open-label, randomized, cross-over, two-sequence and two-period design. Subjects were genotyped for 3435C>T and 1236C>T single-nucleotide polymorphisms. A linear mixed model was performed to compare pharmacokinetic parameters.

RESULTS

Subjects with 3435T/T genotype vs. C carriers showed a higher area under the concentration-time curve from 0 to 36 h (p=0.01). Subjects classified according to 1236C>T SNP and haplotypes showed no statistically significant differences.

CONCLUSIONS

These results suggest that the polymorphic MDR-1, in particular the 3435C>T allelic variant, might influence plasma levels of quetiapine.

Pharmacokinetic profile of the extended-release formulation of quetiapine fumarate (quetiapine XR): clinical implications

OBJECTIVES

A series of studies were conducted to guide the development and characterise the pharmacokinetics of extended-release quetiapine fumarate (quetiapine XR), a once-daily formulation to control the release of the drug.

METHODS

Data from these studies are described and discussed herein.

RESULTS

Once-daily quetiapine XR produced a similar area under the plasma concentration-time curve (AUC), minimum plasma concentration (Cmin) and a slightly lower maximum plasma concentration (Cmax) than the equivalent dose of immediate-release quetiapine (quetiapine IR) given twice daily. In a crossover, head-to-head study, total daily exposure, measured by AUC at steady state, was less variable with quetiapine XR versus quetiapine IR (percent coefficient of variation 39.2% versus 51.2%, respectively). Compared with fasting, a high-fat meal increased the AUC and Cmax for quetiapine XR, whereas a light meal had no significant effect on these parameters. Quetiapine XR exhibits a less pronounced D2 receptor occupancy peak and receptor occupancy levels remain higher for longer compared with quetiapine IR. Quetiapine XR was generally well tolerated with a safety profile similar to quetiapine IR, although the intensity of sedation in the first hours of treatment was significantly lower (p < 0.01) with quetiapine XR versus IR.

CONCLUSION

At steady state, quetiapine XR provided a similar AUC and Cmin and a slightly lower Cmax relative to an equivalent dose of quetiapine IR administered twice daily. Quetiapine XR exhibited linear pharmacokinetics in the dose range tested and no food effect was observed with a light meal. Once-daily dosing and simpler dose titration makes using quetiapine XR convenient for clinicians and patients. Quetiapine XR has predictable pharmacokinetics and was generally well tolerated, with significantly lower intensity of sedation after the first hours of administration compared with quetiapine IR. With once-daily quetiapine XR, the impact of daytime sedation may be mitigated by evening dosing.

Development and validation of a sensitive and robust LC-MS/MS with electrospray ionization method for simultaneous quantitation of quetiapine and its active metabolite norquetiapine in human plasma

BACKGROUND

Quetiapine is an atypical antipsychotic agent for the treatment of schizophrenia, acute mania, and acute bipolar depression. The antidepressive response is considered to be mediated by the metabolite norquetiapine (N-desalkylquetiapine), and the aim of this study was to develop an LC-MS/MS method to measure concentrations of these compounds in human plasma.

METHODS

Following one step liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a Sunfire C18 column (50mm×2.1mm, 5μm). The retention times were 2.12, 2.24, 2.12 and 2.19min for quetiapine, norquetiapine and their respective stable labeled internal standards, respectively. Cycle time was 4min. Selected reaction monitoring (SRM) in positive ion mode was used for quantitation.

RESULTS

The present method exhibited a linear dynamic range of 0.5-500ng/ml for quetiapine and 0.6-600ng/ml for norquetiapine. The applicable range was extended by dilution up to 5-fold with blank matrix. The accuracy and precision for quetiapine were <103.0% and 8.8%, for norquetiapine were <108.8% and 11.1%, respectively.

CONCLUSIONS

A rapid, sensitive, and robust LC-MS/MS method for quantifying quetiapine and its metabolite norquetiapine levels in human plasma was validated and successfully applied to samples from schizophrenic patients in clinical pharmacokinetics studies.

The toxicology and comorbidities of fatal cases involving quetiapine

The use of quetiapine in Australia has increased rapidly in recent years. Anecdotal and post-marketing surveillance reports indicate an increase in quetiapine misuse in prisons as well as an increase in its availability on the black-market. This study examined a cohort of quetiapine-associated deaths occurring in Victoria, Australia, between 2001 and 2009, to determine the prevalence of deaths associated with this drug and to determine whether misuse represents a legitimate concern. Case details were extracted from the National Coronial Information System. There were 224 cases with an average age of 43 years of age (range 15-87 years). The cause of death was mostly drug toxicity (n = 114, 51 %), followed by natural disease (n = 60, 27 %), external injury (n = 31, 14 %) and unascertained causes (n = 19, 8 %). Depression and/or anxiety were common, observed in over a third of the cohort (80 cases, 36 %). About 20 % of cases did not mention a psychiatric diagnosis at all which raises the question of whether quetiapine had been prescribed correctly in these cases. Cardiovascular disease was the most commonly reported illness after mental disease. Quetiapine ranged in concentration from the limit of reporting (0.01 mg/L) to 110 mg/L. The median concentration of quetiapine was much lower in the natural disease deaths (0.25 mg/L) compared with drug caused deaths (0.7 mg/L). The most commonly co-administered drug was diazepam in 81 (36 %) cases. There were a small number of cases where quetiapine contributed to a death where it had not apparently been prescribed, including the death of a 15 year old boy and one of a 34 year old female. Overall, misuse of quetiapine did not appear to be a significant issue in this cohort; use of the drug only occasionally led to fatalities when used in excess or concomitantly with interacting drugs. However, considering that it is a recent social concern, it is possible that analysis of cases post 2009 would reveal more cases of quetiapine abuse. Close monitoring of quetiapine is therefore advised to prevent adverse outcomes, particularly in vulnerable populations such as substance abusers.

Quantification of quetiapine in human plasma by reverse phase high performance liquid chromatography

The objective of the present investigation is to develop and validate a simple, economical and reliable high performance liquid chromatography method for the quantification of quetiapine (CAS 111974-72-2) in human plasma with a quantification limit sufficiently low to support pharmacokinetic studies. Imipramine hydrochloride (CAS 113-52-0) was used as internal standard. The validated method allows quantification of quetiapine in 15-1000 ng/mL. The method was shown to be precise (< 7% coefficient of variation, CV) and accurate (< or = 10% relative error, RE). The correlation coefficient for quetiapine was > 0.9970. The simplicity of the assay and rapid liquid-liquid extraction make it an attractive procedure in high-throughput bioanalysis of quetiapine.

Atypical antipsychotic administration during late pregnancy: placental passage and obstetrical outcomes

OBJECTIVES

There are limited data regarding the use of atypical antipsychotic medications in pregnancy. The objectives of the current study were to quantify placental permeability to antipsychotic medications and to document obstetrical outcomes for women taking these agents proximate to delivery.

METHOD

The authors conducted a prospective observational study of women treated with an atypical antipsychotic or haloperidol during pregnancy. Maternal and umbilical cord plasma samples collected at delivery were analyzed for medication concentrations. Placental passage was defined as the ratio of umbilical cord to maternal plasma concentrations (ng/ml). Obstetrical outcome was ascertained through maternal reports and reviews of obstetrical records.

RESULTS

Fifty-four pregnant women with laboratory-confirmed antipsychotic use proximate to delivery were included in the analysis. Complete maternal-infant sample pairs were available for 50 participants. Placental passage ratio was highest for olanzapine (mean=72.1%, SD=42.0%), followed by haloperidol (mean=65.5%, SD=40.3%), risperidone (mean=49.2%, SD=33.9%), and quetiapine (mean=23.8%, SD=11.0%). There were tendencies toward higher rates of low birth weight (30.8%) and neonatal intensive care unit admission (30.8%) among neonates exposed to olanzapine.

CONCLUSIONS

All four antipsychotics demonstrated incomplete placental passage. Quetiapine demonstrated the lowest placental passage of the medications studied. These novel data provide an initial quantification of the placental passage of antipsychotics and fetal exposure in humans, demonstrating significant differences between individual medications.

Therapeutic drug monitoring of quetiapine in adolescents with psychotic disorders

INTRODUCTION

There are developmental and age-dependent differences in the pharmacokinetics and the pharmacodynamics of drugs in children and adolescents. Therefore, there is a need to carry out standardised studies to find out therapeutic ranges of plasma/serum concentrations in psychopharmacotherapy of children and adolescents. The aim of this prospective study was to examine the relationship between quetiapine serum concentration, treatment response, and side effects in a clinical setting to elucidate the age-specific therapeutic range of quetiapine in adolescents.

METHODS

Over a period of two years, therapeutic drug monitoring (TDM) was routinely performed in 21 adolescents (mean age was 15.9+/-1.5 years, 57% male) with psychotic disorders according to the guidelines of the AGNP TDM expert group. The psychopathology was assessed by using the Clinical Global Impression Scale (CGI) and the Brief Psychiatric Rating Scale (BPRS). Side effects were assessed by using the Dose Record and Treatment Emergent Symptom Scale (DOTES). Trough quetiapine concentrations were determined under steady state conditions after multiple-dose regimes (median 600 mg/day; range 100-800 mg/day).

RESULTS

There was a marked variability of the serum concentrations, ranging from 19-877 ng/ml. 40.8% of the determined values were below and 24.5% above the therapeutic range (70-170 ng/ml) recommended for adults. None of the patients had severe side effects. We found a weak correlation between dose and serum concentration of quetiapine and no relationship between serum concentration and treatment response.

DISCUSSION

There are several limitations of this study, and our results should therefore be interpreted with caution. Notwithstanding, differences in the ontogenesis of pharmacokinetics and pharmacodynamics may be the reason for the difference in the relationship between blood concentrations and therapeutic response to psychopharmaca in children, adolescents and adults. Further studies using larger samples, baseline assessment of psychopathology, definition of the treatment interval and investigation of clinically relevant interactions with various co-medications are warranted to improve the limitations of this pilot study.

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.

Quetiapine and breast feeding

OBJECTIVE

To quantify the relative infant dose of quetiapine during breast feeding, describe the milk:plasma (M:P) ratio, and determine the well-being of the exposed infant.

CASE SUMMARY

A 26-year-old mother and her 3-month-old son were studied over a 24 hour quetiapine dose interval at steady-state. Quetiapine concentrations were quantified by high-performance liquid chromatography. Infant exposure was calculated as the concentration in milk multiplied by an estimated milk production of 0.15 L/kg/day and normalized to the weight-adjusted maternal dose. The average concentration in milk was 41 microg/L, the M:P ratio (measured using average concentrations in the elimination phase) was 0.29, and the relative infant dose was 0.09% of the maternal weight-adjusted dose (7273 microg/kg/day). The infant plasma concentration of 1.4 microg/L was some 6% of the corresponding maternal plasma concentration. No adverse effects were noted in the infant.

DISCUSSION

Our findings of an infant exposure to quetiapine of less than 0.1% of the maternal dose and a lack of adverse effects confirm and extend the findings of 2 previous studies.

CONCLUSIONS

Although limited, the data shown here support the prescription of quetiapine to a breast-feeding mother following a careful individual risk/benefit analysis. We suggest regular monitoring of infant progress and occasional measurement of quetiapine in the infant's plasma.

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.

Simultaneous determination of fluvoxamine isomers and quetiapine in human plasma by means of high-performance liquid chromatography

An original HPLC-UV method has been developed for the simultaneous determination of the atypical antipsychotic quetiapine and the geometric isomers of the second-generation antidepressant fluvoxamine. The analytes were separated on a reversed-phase C8 column (150 mm x 4.6mm i.d., 5 microm) using a mobile phase composed of acetonitrile (30%) and a 10.5mM, pH 3.5 phosphate buffer containing 0.12% triethylamine (70%). The flow rate was 1.2 mL min(-1) and the detection wavelength was 245 nm. Sample pretreatment was carried out by an original solid-phase extraction procedure using mixed-mode cation exchange (DSC-MCAX) cartridges; only 300 microL of plasma were needed for one analysis. Citalopram was used as the internal standard. The method was validated in terms of linearity, extraction yield, precision and accuracy. Good linearity was obtained in plasma over the 5.0-160.0 ng mL(-1) concentration range for each fluvoxamine isomer and over the 2.5-400.0 ng mL(-1) concentration range for quetiapine. Extraction yield values were always higher than 93%, with precision (expressed as relative standard deviation values) better than 4.0%. The method was successfully applied to human plasma samples drawn from patients undergoing polypharmacy with the two drugs. Satisfactory accuracy values were obtained, with mean recovery higher than 94%.

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.

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.

Automated analysis of quetiapine and other antipsychotic drugs in human blood by high performance-liquid chromatography with column-switching and spectrophotometric detection

An automated HPLC method with column switching is described for the determination of quetiapine, clozapine, perazine, olanzapine and metabolites in blood serum. After clean-up on silica C8 material (20 microm particle size) drugs were separated on ODS Hypersil C18 material (5 microm; column size 250 mm x 4.6 mm i.d.) within 25 min and quantified by ultraviolet (UV) detection at 254 nm. The limit of quantification ranged between 10 and 50 ng/ml. At therapeutic concentrations of the drugs, the inter-assay reproducibility was below 10%. Analyses of drug concentrations in serum of 75-295 patients treated with therapeutic doses of the antipsychotic drugs revealed mean+/-S.D. steady state concentrations of 139+/-136 ng/ml for quetiapine, 328+/-195 ng/ml for clozapine, 48+/-27 ng/ml for olanzapine and 71+/-52 ng/ml for perazine. The method was thus suitable for routine therapeutic drug monitoring and may be extended to other drugs.

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.

Case Studies of Postmortem Quetiapine: Therapeutic or Toxic Concentrations?

The focus of this study was to determine if the analysis of a variety of postmortem biological specimens would aid in the toxicological interpretation of quetiapine in the cause and manner of death determinations. Postmortem quetiapine concentrations were examined in 21 medical examiner cases using liquid-liquid extraction and high-performance liquid chromatography analysis. Specimens analyzed were peripheral blood, central blood, liver, vitreous humor, and gastric contents, when available. Findings from this study suggest that therapeutic postmortem quetiapine concentrations may be less than 1 mg/L in both peripheral and central blood, less than 0.5 mg/L in vitreous, and less than 5 mg/kg in liver. Quetiapine concentrations indicative of toxicity were estimated at greater than 1 mg/L in peripheral and central blood, greater than 0.5 mg/L in vitreous, and greater than 5 mg/kg in the liver. Liver concentrations appeared to be particularly helpful in determining the potential for toxicity when compared with blood concentrations. Cases in which quetiapine was determined to play a significant role in the death indicated postmortem liver concentrations greater than 5 mg/kg. Cases in which quetiapine concentrations were considered incidental or noncontributory in the death had liver concentrations 2 mg/kg or less.

A liquid chromatographic-electrospray-tandem mass spectrometric method for quantitation of quetiapine in human plasma and liver microsomes: application to study in vitro metabolism

Quetiapine is an atypical antipsychotic agent for the treatment of schizophrenia. After an oral dose it is absorbed rapidly and extensively metabolized in the liver, resulting in low plasma concentrations of the parent drug. A sensitive analytical method is needed. A liquid chromatographic-electrospray-tandem mass spectrometric (LC-ESI-MS-MS) method combined with a simple liquid-liquid extraction has been developed for the measurement of quetiapine in human plasma and in human liver microsomes (HLM). Clozapine is used as internal standard. Plasma samples or microsomes quenched with methanol (100 microL) were made basic and extracted with 3 mL n-butyl chloride. The reconstituted extracts were analyzed by LC-ESI-MS-MS. Selective reaction monitoring of MH(+) at m/z 384 and 327 resulted in strong fragment ions at m/z 253 and 192 for quetiapine and clozapine, respectively. Recovery of quetiapine and clozapine ranged from 62 to 73%. Intrarun accuracy and precision determined at 1.0 (lower limit of quantitation), 2.5, 200, and 400 ng/mL did not exceed 7% deviation from target and the %CV did not exceed 5.5%. The % target +/- %CV for interrun accuracy and precision were at least 95% +/- 7.4% at concentrations of 2.5, 200, and 400 ng/mL. Plasma samples (2.5 and 400 ng/mL) stored at room temperature for 24 h or after 3 cycles of freeze/thaw were all stable (maximum % deviation < or = 11.0%). Processed extracts (2.5 and 400 ng/mL) stored for 7 days at -20 degrees C or 6 days on the autosampler were all stable (maximum % deviation < or = 11.5%). The method has been used to study quetiapine utilization during incubation with HLM or with cDNA-expressed human cytochrom P450s (CYP). Quetiapine is extensively metabolized by CYP 3A4 and CYP 2D6 and to a lesser extent by CYP 3A7, CYP 3A5, and CYP 2C19.

Quetiapine serum concentrations in psychiatric patients: the influence of comedication

Steady-state serum concentrations of quetiapine were recorded in 62 psychiatric patients under routine conditions. Doses were administered twice daily, and serum quetiapine levels were measured in the morning about 12 hours after the last dose. Eight patients were in monotherapy, whereas the rest received various additional psychotropic drugs. For the whole group, the concentration-to-dose ratio (C/D) varied 238-fold, with a median value of 0.41 nmol/L/(mg/24 h). For the administered dose range (37.5-1200 mg/24 h), the serum concentrations ranged from below the detection limit (10 nmol/L) to 999 nmol/L. With the exception of 2 subjects receiving carbamazepine and patients receiving quetiapine outside the recommended dose interval, 80% of the rest had serum levels within the range 50 to 650 nmol/L, which may serve as an orienting interval for serum concentrations observed under routine treatment conditions. Patients (n = 38) comedicated with drugs competing for metabolism by CYP3A4 displayed a median C/D value of 0.48 nmol/L/(mg/24 h), which was 70% higher than the C/D value of the monotherapy group [0.28 nmol/L/(mg/24 h)], in contrast to patients receiving drugs metabolized by CYP2D6 with a median C/D of 0.23 nmol/L/(mg/24 h). None of the comedicated groups were significantly different from the monotherapy group. Two subjects comedicated with carbamazepine had very low C/D values [0.02-0.04 nmol/L/(mg/24 h)].

Metabolic mechanism of quetiapine in vivo with clinical therapeutic dose

The in vivo metabolic mechanism of quetiapine (QTP) with clinical therapeutic dose was studied. Nineteen patients received multiple doses of QTP with or without concomitant erythromycin. Midazolam was given to detect enzyme activity. Plasma Concentrations of QTP, midazolam, and their metabolites were measured at specified time intervals. In presence of erythromycin, activity of CYP3A4 decreased significantly; for QTP, C(max), AUC(0-24), and t(1/2) increased significantly, CL decreased significantly, and variations in AUC(0-24) and CL showed, respectively, significant negative and positive correlation to that of CYP3A4 activity; for QTP sulfoxide (QTP-SF), C(max) and AUC(0-24) decreased significantly, t(1/2) increased significantly, and variation of t(1/2) was significantly positively correlated to that of CYP3A4 activity; for 7-hydroxy-quetiapine (QTP-H), t(1/2) increased significantly and was closely correlated to CYP3A4 activity; for 7-hydroxy-N-desalkyl-quetiapine (QTP-ND), C(max) and AUC(0-24) decreased significantly, and variation of AUC(0-24) was significantly positively correlated to that of CYP3A4 activity. In conclusion, the major metabolic pathway of QTP is sulfoxidation. CYP3A4 is the primary enzyme responsible for CYP-mediated metabolism of QTP in clinical therapy dosage in vivo. QTP sulfoxidation and N-dealkylation are mainly catalyzed by CYP3A4. 7-Hydroxylation of QTP is not mainly catalyzed by CYP3A4. The metabolism of QTP-SF and QTP-H is mainly catalyzed by CYP3A4, but QTP-ND is not by CYP3A4.

Effect of erythromycin on metabolism of quetiapine in Chinese suffering from schizophrenia

OBJECTIVE

To study the effect of erythromycin on metabolism of quetiapine in Chinese suffering from schizophrenia.

METHODS

Nineteen patients received multiple doses of quetiapine (200 mg, twice daily) with or without co-administered erythromycin (500 mg, three times daily). Blood samples were collected at specified time intervals for determination of plasma concentrations of quetiapine and some of its metabolites.

RESULTS

With erythromycin co-administration: for quetiapine, maximal plasma concentration (Cmax), area under concentration-time curve of 0-infinity h (AUC0-infinity) and terminal-phase elimination half-life time (t1/2) increased 68, 129 and 92%, respectively, and clearance (CL) and terminal elimination rate constant (Ke) decreased 52% and 55%, respectively; for quetiapine sulfoxide (QTP-SF), Cmax, AUC0-infinity and AUC ratio decreased 64, 23, and 70%, respectively, and t1/2 increased 211%; for 7-hydroxy-quetiapine (QTP-H), Ke and AUC ratio decreased 61% and 45%, respectively, and t1/2 increased 203%; for 7-hydroxy-N-desalkyl-quetiapine (QTP-ND), Cmax, AUC0-infinity and AUC ratio decreased 36, 40 and 71%, respectively.

CONCLUSION

Erythromycin has a noticeable effect on the metabolism of quetiapine. When quetiapine is co-administered with CYP3A inhibitors such as erythromycin, the dosing regimen should be modified according to quetiapine TDM.

Simultaneous determination of clozapine, olanzapine, risperidone and quetiapine in plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry

Clozapine (CLZ), olanzapine (OLZ), risperidone (RIP) and quetiapine (QTP) have been widely used in the treatment of schizophrenia. However, no study (or little study) has been conducted to determine the four drugs simultaneously by the use of high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-MS/ESI).

OBJECTIVE

To develop a sensitive method for simultaneous determination of CLZ, OLZ, RIP and QTP in human plasma by HPLC-MS/ESI.

METHODS

The analytes were extracted twice by ether after samples had been alkalinized. The HPLC separation of the analytes was performed on a MACHEREY-NAGEL C(18) (2.0 mm x 125 mm, 3 microm, Germany) column, using water (formic acid: 2.70 mmol/l, ammonium acetate: 10 mmol/l)-acetonitrile (53:47) as mobile phase, with a flow-rate of 0.16 ml/min. The compounds were ionized in the electrospray ionization (ESI) ion source of the mass spectrometer and were detected in the selected ion recording (SIR) mode.

RESULTS

The calibration curves were linear in the ranges of 20-1000 ng/ml for CLZ and QTP, 1-50 ng/ml for OLZ and RIP, respectively. The average extraction recoveries for all the four analysts were at least above 80%. The methodology recoveries were higher than 91% for the analysts. The intra- and inter-day R.S.D. were less than 15%.

CONCLUSION

The method is accurate, sensitive and simple for routine therapeutic drug monitoring (TDM) and for the study of the pharmacokinetics of the four drugs.

Postmortem Distribution of the Novel Antipsychotic Drug Quetiapine

The objective of this research was to determine the concentrations and distribution of the atypical antipsychotic drug, quetiapine, in postmortem tissues from eight Medical Examiner cases. Quetiapine was isolated from liquid specimens and tissue homogenates by extraction at an alkaline pH into 1-chlorobutane. The 1-chlorobutane was decanted, and quetiapine, plus the internal standard (prochlorperazine), was back-extracted into 0.1N sulfuric acid. The acid layer was made basic, and quetiapine, plus the internal standard, was re-extracted into 1-chlorobutane. Quantitation was by gradient, high-pressure liquid chromatography on a C-8 ODS (2.1 x 150 mm, 5 mu) column with acetonitrile/0.1M ammonium hydroxide (pH 10) mobile phase and a photodiode array detector set at 258 nm. The apparent linear range of the assay was from 0.05 to 5.0 microg/mL. At known concentrations of 0.1 and 0.5, interday accuracy (n = 5) was 103.8 and 107.2%, respectively. Interday precision (% cv) at the same concentrations was 9.8 and 9.0, respectively. In the cases where quetiapine was not considered to have contributed to the death, the postmortem concentrations in blood, liver, and bile ranged between 0.15 and 2.7 mg/L (n = 6), 1.3 and 9.5 mg/kg (n = 8), and 10 and 46 mg/L (n = 5), respectively. In the one case involving a quetiapine overdose, concentrations in blood (19.8 mg/L), liver (12.6 mg/kg), and bile (161 mg/L) exceeded the ranges of concentrations determined in specimens from the quetiapine-unrelated deaths.

Simultaneous determination of quetiapine and three metabolites in human plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry

AIM

To develop a high performance liquid chromatography-electrospray mass spectrometry (HPLC-MS/ESI) method for simultaneous determination of quetiapine and its sulfoxide-, 7-hydroxy-, 7-hydroxy-N-dealkyl-metabolites in human plasma.

METHODS

The HPLC separation of the compounds was performed on a Kromasil C18, (5 microm, 4.6 mm.150 mm) column, using water (formic acid: 1.70 mmol/L, ammonium acetate: 5.8 mmol/L)-acetonitrile (65:35) as mobile phase, with a flow-rate of 0.95 mL/min. The compounds were ionized in the electrospray ionization (ESI) ion source of the mass spectrometer and detected in the selected ion recording (SIR) mode. The samples were extracted using solid-phase extraction columns.

RESULTS

The calibration curves were linear in the ranges of 10-2000 microg/L for quetiapine, 1-200 microg/L for its metabolites, respectively. The average extraction recoveries for all the four samples were above 85 %. The methodology recoveries were much higher than 95 %. The intra-day and inter-day RSD are less than 15 %.

CONCLUSION

The method is accurate, sensitive, and simple for study of pharmacokinetics and metabolic mechanism of quetiapine in patients at therapeutic dose.

Fully automated on-line quantification of quetiapine in human serum by solid phase extraction and liquid chromatography

A quantitative method for determination of quetiapine (QTP) in human serum is presented. The method is fully automated and based on high performance liquid chromatography (HPLC) with on-line solid phase extraction (SPE). The extraction procedure is based on a C2 cartridge, which is eluted with methanol. The eluate is injected onto a silica column with a mobile phase consisting of methanol:20 mM NH(4)CH(3)COO, pH 5.0 (99:1). Quetiapine is quantified by ultra-violet (UV) absorbance at 257 nM with trifluoperazine as the internal standard (I.S.). The extraction recoveries for quetiapine and trifluoperazine were 69 and 57%, respectively. The total inter day coefficient of variation was 11.1, 3.8 and 3.1% at 20, 500 and 1000 nM, respectively. The detection limit was 10.3 nM quetiapine. The method has been used in our therapeutic drug monitoring (TDM) laboratory where co-administered drugs often are observed. In an investigation of analytical interference from co-administered drugs, demethyl-mianserine was the only drug which interfered with the internal standard. There was no interference with quetiapine itself. The method showed good agreement with mass spectrometric quantification of quetiapine.

Quetiapine poisoning

STUDY OBJECTIVE

We describe the effects of quetiapine in overdose.

METHODS

Quetiapine poisonings were identified from a prospective database of poisoning admissions to a regional toxicology service. Data extracted included details of ingestion, clinical features, investigations (including ECG), and other outcomes (length of stay and ICU admission rate).

RESULTS

There were 45 cases of quetiapine overdose, of which 18 patients with quetiapine assay results were included. Median length of stay was 35 hours (interquartile range [IQR] 14 to 42 hours) for the 18 patients, and 9 were admitted to the ICU. The median ingested dose was 3.5 g (IQR 1.7 to 6.2 g), and reported ingested dose was highly correlated with estimated peak drug concentration (r(2)=0.84; P<.0001), confirming patient-provided history of ingestion. Seizures occurred in 2 patients, delirium occurred in 3 patients, and mechanical ventilation was required in 4 patients. No arrhythmias or deaths occurred. Six of the 18 patients ingested quetiapine alone, with a median length of stay of 35 hours, and 3 were admitted to the ICU. In 1 patient who ingested 24 g, hypotension and seizures occurred. For 10 patients for whom ECGs were available and who had ingested no cardiotoxic drugs, tachycardia occurred in 8 patients. For these 10 patients, the mean corrected QT (QTc) interval was increased at 487 ms, but the mean uncorrected QT interval was 349 ms. Reported dose and peak quetiapine concentrations were significantly associated with ICU admission and length of stay more than 24 hours. A reported dose less than 3 g and a Glasgow Coma Scale score not less than 15 predicted patients not requiring ICU admission or length of stay more than 24 hours.

CONCLUSION

Quetiapine overdose causes central nervous system depression and sinus tachycardia. In large overdoses, patients may require intubation and ventilation for associated respiratory depression. Although a prolonged QTc occurs, its clinical significance is unclear because it is most likely caused by an overcorrection caused by the tachycardia. In our experience, a reported dose of less than 3 g for patients who are not drowsy (with a Glasgow Coma Scale score of 15) at least 4 hours after ingestion and who did not coingest another toxic agent defined a group not requiring ICU admission or inpatient admission greater than 24 hours.

HPLC analysis of the novel antipsychotic drug quetiapine in human plasma

A precise and feasible high-performance liquid chromatographic (HPLC) method for the analysis of the novel antipsychotic drug quetiapine in plasma has been developed. The analysis was carried out on a C8 (150x4.6 mm i.d., 5 micrometer) reversed-phase column, using a mixture of acetonitrile, methanol and pH 1.9 phosphate buffer as the mobile phase; triprolidine was used as the internal standard. Careful pretreatment of the biological samples was implemented by means of solid-phase extraction (SPE). A good linearity was found in the 4-400 ng ml(-1) quetiapine plasma concentration range. The application to some plasma samples of patients treated with Seroquel(R) tablets gave satisfactory results. The accuracy was good (quetiapine mean recovery=92%), as well as the precision (mean RSD=3.3%). The method seems to be suitable for the clinical monitoring of patients treated with quetiapine.

Open-label study of the effect of combination quetiapine/lithium therapy on lithium pharmacokinetics and tolerability

OBJECTIVE

The aim of this study was to assess the effect of oral quetiapine on the steady-state pharmacokinetics of lithium.

METHODS

This was an open-label trial in patients with schizophrenia, schizoaffective disorder, or bipolar disorder who had demonstrated tolerability to combination lithium/ antipsychotic therapy. Patients received lithium for at least 1 week before screening and throughout the 18-day trial. Quetiapine was coadministered in fixed, stepwise, increasing doses of 25 to 250 mg TID on days 4 through 11, and maintained at 250 mg TID on days 12 through 14. Blood samples were drawn to monitor plasma concentrations of lithium and quetiapine. Psychiatric assessments included the Brief Psychiatric Rating Scale, the Clinical Global Impression severity of illness item, and the modified Scale for the Assessment of Negative Symptoms. Neurologic function was assessed using the Simpson-Angus Scale and the Abnormal Involuntary Movement Scale. Other assessments included clinical laboratory testing, electrocardiography, physical examinations, and monitoring for spontaneously reported adverse events.

RESULTS

Nine men and 1 woman (mean [SE] age, 32.8 [1.9] years; mean [SE] body weight, 87.6 [3.3] kg) entered and completed the 18-day trial. Eight patients had bipolar disorder, 1 had paranoid schizophrenia, and 1 had schizoaffective disorder. Morning trough concentrations of lithium in serum (days 2, 6, 8, 10, 12, 14, and 17), as well as quetiapine and 2 of its metabolites in plasma (days 12, 13, and 14), did not appear to vary noticeably. Small increases were observed in the mean values of the area under the 12-hour serum lithium concentration-time curve and the maximum and minimum observed serum lithium concentrations when quetiapine was added to the lithium regimen. However, the increases were not considered clinically relevant by the investigators and were not statistically significant. A total of 91 adverse events were reported, 67 (73.6%) of which were not attributed to trial treatment. The most commonly reported adverse events during coadministration of lithium and quetiapine were somnolence (90.0% [9/10]), asthenia (70.0% [7/10]), dry mouth (30.0% [3/10]), nausea (30.0% [3/10]), vomiting (30.0% [3/10]), dizziness (30.0% [3/10]), tremor (30.0% [3/10]), and insomnia (20.0% [2/10]). There were no serious adverse events.

CONCLUSIONS

Measures of lithium and quetiapine concentrations did not vary significantly during combination therapy. Coadministered lithium and quetiapine were well tolerated in the patients studied.

Massive gabapentin and presumptive quetiapine overdose

Previous reports of gabapentin overdose have described mild symptoms of somnolence, ataxia and slurred speech. Quetiapine has produced a false positive for cyclic antidepressants on immunoassay drugscreens. Quetiapine overdose is associated with coma, QTc prolongation and hypotension. We report a case of massive gabapentin and presumptive quetiapine overdose with the highest recorded serum gabapentin concentration (104.5 u/ml) associated with coma, respiratory depression requiring mechanical ventilation, and hypotension.

Clinical pharmacokinetics of quetiapine: an atypical antipsychotic

Quetiapine is a dibenzothiazepine derivative that has been evaluated for management of patients with the manifestations of psychotic disorders. In pharmacokinetic studies in humans, quetiapine was rapidly absorbed after oral administration, with median time to reach maximum observed plasma concentration ranging from 1 to 2 hours. The absolute bioavailability is unknown, but the relative bioavailability from orally administered tablets compared with a solution was nearly complete. Food has minimal effects on quetiapine absorption. The drug is approximately 83% bound to serum proteins. Single and multiple dose studies have demonstrated linear pharmacokinetics in the clinical dose range (up to 375mg twice daily). The drug is eliminated with a mean terminal half-life of approximately 7 hours. The primary route of elimination is through hepatic metabolism. In vitro studies show that quetiapine is predominantly metabolised by cytochrome P450 (CYP) 3A4. After administration of [14C]quetiapine, approximately 73% of the radioactivity was excreted in the urine and 21% in faeces. Quetiapine accounted for less than 1% of the excreted radioactivity. 11 metabolites formed through hepatic oxidation have been identified. Two were found to be pharmacologically active, but they circulate in plasma at 2 to 12% of the concentration of quetiapine and are unlikely to contribute substantially to the pharmacological effects of the drug. The pharmacokinetics of quetiapine do not appear to be altered by cigarette smoking. Oral clearance declines with age, and was reduced in 2 of 8 patients with hepatic dysfunction but not in patients with renal impairment. Quetiapine has no effect on the in vitro activity of CYP1A2, 2C9, 2C19, 2D6 and 3A4 at clinically relevant concentrations. The lack of effect of quetiapine on hepatic oxidation was confirmed in vivo by the lack of effect of quetiapine on antipyrine disposition. Quetiapine had no effect on serum lithium concentration. Phenytoin and thioridazine increase the clearance of quetiapine, and ketoconazole decreases clearance. No clinically significant effects of cimetidine, haloperidol, risperidone or imipramine on the pharmacokinetics of quetiapine were noted. Quetiapine dosage adjustment, therefore, may be necessary when coadministered with phenytoin, thioridazine or other potent CYP3A4 inducers or inhibitors. The relationship between the therapeutic effects and the plasma concentrations of quetiapine has been investigated in a multicentre clinical trial. There was no statistically significant association between trough plasma quetiapine concentration and clinical response as measured by traditional assessments of psychotic symptom severity. Subsequent clinical studies of the plasma concentration versus effect relationships for quetiapine may help to further define guidelines for dosage regimen design.

Asymptomatic QTc prolongation associated with quetiapine fumarate overdose in a patient being treated with risperidone

We report a patient who ingested a 2000-mg overdose of quetiapine fumarate (Seroquel). Her maintenance medications also included risperidone, venlafaxine, topiramate, and clonazepam. On presentation, she was drowsy, but had no other significant CNS signs and no cardiac symptoms or abnormal physical signs. Approximately 2 h after the quetiapine ingestion, an electrocardiogram (ECG) showed normal sinus rhythm at 95 beats/min with a corrected QT (QTc) interval of 537 ms (upper limit of normal = 440 ms). Plasma quetiapine concentration at that time was 1800 ng/ml. Continuous ECG monitoring for the subsequent 18 h did not reveal any episode of ventricular tachycardia. A 12-lead ECG 18 h post-overdose was normal with a QTc interval of 401 ms and the corresponding plasma quetiapine concentration was 160 ng/ml. She made an uneventful medical recovery from the toxic ingestion. This case suggests that when patients overdose on quetiapine while taking therapeutic doses of risperidone, such overdoses, even if not massive, can cause considerable QTc interval prolongation. We recommend that quetiapine overdose patients undergo continuous ECG monitoring for 12-18 h post-ingestion.

Quetiapine fumarate overdose: clinical and pharmacokinetic lessons from extreme conditions

BACKGROUND

Although the new atypical antipsychotic, quetiapine fumarate, is growing in popularity over its progenitor, clozapine, clinical experience with overdose of this agent remains limited. Observation of an overdose situation provided a unique opportunity to define the safety, clinical effects, and pharmacokinetics of this medication more clearly.

METHODS

A patient admitted immediately after ingesting an overdose of 30 tablets of 100 mg of quetiapine was observed carefully to document effects of the medication. These observations were compared with the only two other published cases of overdose, to the known pharmacology of the drug, and to serial measurements of serum drug concentrations obtained to document the time course of elimination of the drug.

RESULTS

Consistent with the two previously published cases, the main clinical effects of overdose were hypotension, tachycardia, and somnolence as predicted by its known alpha-adrenergic receptor and histamine receptor blockade. These effects were managed with fluid resuscitation and supportive measures. No cardiac arrhythmias other than tachycardia have been reported, but the tachycardia was of an unexpectedly long duration in this case. Decline in serum quetiapine concentration followed a biexponential pattern with a terminal elimination half-life of 22 hours. Unexpectedly low peak serum concentrations in three patients with overdose suggest that absorption is highly reduced, either by the effects of the overdose or by the activated charcoal administered.

CONCLUSIONS

Quetiapine appears to have greater safety in overdose than traditional antipsychotic agents. Its toxicity is consistent with its receptor pharmacology. Elevated serum concentrations associated with this overdose remained above the limit of detection long enough to document a terminal elimination half-life of 22 hours in this patient. This is much more consistent with previously noted duration of clinical effects and detectable serum concentrations after overdose than the published half-life of 6 hours. Physicians should be aware that any new drug that is active at low concentrations may have had its half-life underestimated during preclinical development because of the difficulty in detecting the drug after the distribution phase has ended.

Quetiapine (Seroquel) concentrations in seven postmortem cases

Quetiapine is a new antipsychotic drug that has been available in the United States since September 1997. It belongs to a new chemical class of drugs called the dibenzothiazepine derivatives and is easily detected with a basic drug screen. The Los Angeles County Department of Coroner Toxicology Laboratory has encountered quetiapine in seven postmortem cases. Tissue distributions were determined in each of the seven cases. The analysis of quetiapine from postmortem specimens consisted of an n-butylchloride basic extraction with presumptive identification and quantitation on a gas chromatograph-nitrogen-phosphorus detector. Linearity was achieved from 0.10 to 3.0 mg/L with a limit of quantitation of 0.10 mg/L. Confirmation of quetiapine was performed on a gas chromatograph-mass spectrometer by comparison with a pure analytical standard. The tissue distribution of quetiapine was as follows: heart blood present, but less than (+<) 0.10-49 mg/L (seven cases); femoral blood +< 0.10-1.4 mg/L (five cases); liver +< 0.10-112 mg/kg (five cases); spleen 4.0 mg/kg (one case); urine 0-3.0 mg/L (two cases); bile 0.60-7.5 mg/L (three cases); and gastric contents +< 0.01-18 mg total (five cases). To our knowledge, this is the first report of the presence of quetiapine in postmortem specimens.

Analysis and pharmacokinetics of quetiapine and two metabolites in human plasma using reversed-phase HPLC with ultraviolet and electrochemical detection

A sensitive and specific HPLC assay for the measurement of the antipsychotic compound quetiapine in human plasma has been developed and validated. The assay employs a three-step liquid liquid extraction of quetiapine and its 7-hydroxylated and 7-hydroxylated, N-dealkylated metabolites from human plasma, and utilizes ultraviolet (UV) detection of quetiapine and electrochemical detection of the metabolites. The method provides a linear response from a quantitation limit of 2.50 to 500 ng ml(-1) for each analyte using 0.4 ml plasma. The assay is applicable from 500 to 5000 ng ml(-1) by sample dilution with de-ionized water. The inter-assay precision of quetiapine in plasma calibration standards across 4 validation days averaged 11.9% relative standard deviation (RSD) over the range 2.50 to 500 ng ml(-1), with intra-assay precision averaging 16.0% RSD and mean accuracy of 98.6% of theory. Similarly, the inter-assay precision of the 7-hydroxylated metabolite in plasma calibration standards across 4 validation days averaged 13.7% RSD over the range 2.50 to 500 ng ml(-1), with intra-assay precision averaging 17.6% RSD and mean accuracy of 109% of theory. The 7-hydroxylated, N-dealkylated metabolite demonstrated inter-assay precision of 16.2% RSD, intra-assay precision of 19.9% RSD, and mean accuracy of 104% of theory over the range 2.50 to 500 ng ml(-1). The present assay method was used to support a study comparing the pharmacokinetic profile of quetiapine with the time course of dopamine D2 and serotonin 5-HT2 receptor occupancy in the brain using positron emission tomography (PET). We describe in this paper the bioanalytical method and the plasma concentrations of quetiapine and its metabolites resulting from this study.

A method for rapid determination of zotepine by gas chromatography-mass spectrometry

A rapid and sensitive method using solid-phase extraction and gas chromatography-mass spectrometry (GC-MS) has been developed for the determination of zotepine (ZTP), an atypical neuroleptic, in human plasma. The detection limit of ZTP was 1 microgram/L. Standard curves over the concentration range from 2.5 to 100 micrograms/L had a good linearity. Intraassay variability ranged from 2.2 to 3.3% and interassay variability from 3.5 to 6.6% at the concentration range of 5-75 micrograms/L. Our preliminary data of single-dose kinetics of ZTP by using this method suggested that the peak time and elimination half-life was much longer than previously reported, and that there appeared to be a second peak after 10-12 h of ZTP administration, indicating the possibility of the presence of enterohepatic recirculation.

Determination of an antipsychotic agent (ICI 204,636) and its 7-hydroxy metabolite in human plasma by high-performance liquid chromatography and gas chromatography—mass spectrometry

ICI 204,636 (I) is an orally active antipsychotic agent under development for the treatment of schizophrenia in humans. It is partially converted in animals to an active 7-hydroxy metabolite (II). Methods were developed for the simultaneous determination of both analytes in human plasma using high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The analytes were extracted from plasma using phenyl solid-phase extraction columns. Quantification by isocratic HPLC was performed in the reversed-phase mode with detection at 250 nm. Extracts were derivatized to trimethylsilyl ethers for quantification by GC-MS using selected-ion monitoring. Both assays were evaluated for consistency of response, precision, accuracy and specificity. Limits of quantification for I and II by HPLC were 15 and 20 ng/ml, respectively; limits of quantification for I and II by GC-MS were 2 and 5 ng/ml, respectively. Both methods were applied to the analysis of clinical samples from oral dosing studies with I.