Determination of clozapine and its major metabolites in serum samples of adolescent schizophrenic patients by high-performance liquid chromatography. Data from a prospective clinical trial

A Systematic Review of Clozapine Concentration-Dose Ratio from Therapeutic Drug Monitoring Studies in Children and Adolescents Treated with Clozapine for Mental Disorders

BACKGROUND

Therapeutic drug monitoring of clozapine in children and adolescents has received insufficient attention. Calculation of concentration-to-dose (C/D) ratios from trough steady-state concentrations estimate drug clearance.

METHODS

A systematic electronic literature search was conducted in 3 article databases from inception until January 10, 2023, and articles reporting clozapine concentrations in children and adolescents were retrieved. The pharmacokinetic quality of the studies was assessed, and clozapine C/D ratios were calculated using the sample mean clozapine dose and concentration.

RESULTS

Of the 37 articles of potential interest, only 7 reported clozapine trough and steady-state concentrations. After excluding case reports and a study confounded by fluvoxamine, 4 studies on psychosis from Europe and the United States were included. The clozapine C/D ratios were similar to published adult values and ranged from 0.82 to 1.24 with a weighted mean of 1.08 ng/mL per mg/d. The weighted means were 334 mg/d for the dose and 380 ng/mL for the concentration. The stratified analysis of the weighted mean clozapine C/D ratios from 2 studies showed lower values in 52 male (1.05 ng/mL per mg/d) than in 46 female (1.46 ng/mL per mg/d) children and adolescents, with values similar to those reported for European adult nonsmokers. Two female adolescents had high clozapine C/D ratios (2.54 ng/mL per mg/d), an Asian American patient with borderline obesity and a patient with intellectual disability with low dosage (mean = 102 mg/d) and concentration (mean = 55 ng/mL).

CONCLUSIONS

Reports on clozapine therapeutic drug monitoring in children and adolescents are limited in number and quality. Future studies should focus on basic pharmacokinetic issues, such as stratification by sex, smoking, and relevant comedications with inductive or inhibitory properties.

Therapeutic drug monitoring of atomoxetine in children and adolescents with attention-deficit/ hyperactivity disorder: a naturalistic study

The selective norepinephrine reuptake inhibitor atomoxetine is potentially among the first-line pharmacotherapy options for ADHD. Therapeutic drug monitoring (TDM) with the quantification and interpretation of atomoxetine serum concentrations is used to determine an individual dose followed by an optimal effectiveness and minimal side effects. The aim of this retrospective pharmacokinetic–pharmacodynamic analysis was to derive age-appropriate recommendations for the implementation of TDM to improve the efficacy and tolerability of atomoxetine in children and adolescents. Using the analytical method of high-performance liquid chromatography with UV detection, 94 serum concentrations of 74 patients between 6 and 21 years of age were determined. Therapeutic effectiveness and side effects were evaluated according to the categories “low”, “moderate”, and “significant”. As part of TDM, a time interval with maximum concentrations of 1–3 h after the administration of atomoxetine was determined for blood sampling. In this time interval, a significant correlation between the weight-normalized dose and the serum concentrations was found. The efficacy as well as the tolerability proved to be mainly moderate or significant. A preliminary therapeutic reference range was between 100 and 400 ng/ml. Naturalistic studies have limitations. Therefore, and due to a limited study population, the results have to be regarded as preliminary observations that must be confirmed in further studies. The preliminary therapeutic reference range for children and adolescents proved to be narrower than the reference range for adult patients. However, due to good efficacy and tolerability an exact reference range remained difficult to determine.

Therapeutic drug monitoring for drugs used in the treatment of substance-related disorders: literature review using a therapeutic drug monitoring appropriateness rating scale

BACKGROUND

The efficacy of drugs for the treatment of substance-related disorders is moderate at best. Therapeutic drug monitoring (TDM) could be an instrument to improve outcomes. Because TDM for most of those drugs is not established, the authors reviewed the literature and built a rating scale to detect the potential added value of TDM for these pharmacologic agents.

METHODS

A literature search was performed for acamprosate, bupropion, buprenorphine, clomethiazole, disulfiram, methadone, naltrexone, and varenicline. The rating scale included 22 items and was divided in five categories: efficacy, toxicity, pharmacokinetics, patient characteristics, and cost-effectiveness. Three reference substances with established TDM were similarly assessed for comparison: clozapine, lithium, and nortriptyline. The three reference substances achieved scores of 15, 12, and 14 points, respectively.

RESULTS

Drugs for treatment of substance-related disorders achieved 3 to 17 points, 17 for methadone, 11 for buprenorphine, 10 for disulfiram, also 10 for naltrexone for the indication opioid-dependence and 9 for the indication alcohol dependence as well as bupropion, 7 points for acamprosate, 6 points for clomethiazole, and 3 for varenicline.

CONCLUSIONS

It is concluded that systematic evaluation of drug- and patient-related variables with the new rating scale can estimate the appropriateness of TDM. Because their rating revealed similar scores as the three reference drugs, it is proposed that TDM should be established for bupropion, buprenorphine, disulfiram or a metabolite, methadone, and naltrexone. An objective rating of drug- and patient-related characteristics could help laboratories focus their method development on the most likely drugs to require TDM along with a thorough drug use evaluation.

Serum Levels of Olanzapine and Its N-desmethyl and 2-hydroxymethyl Metabolites in Child and Adolescent Psychiatric Disorders: Effects of Dose, Diagnosis, Age, Sex, Smoking, and Comedication

The aim of this study was to assess dose-related steady-state serum concentrations of olanzapine (OLZ) and its metabolites N-desmethyl OLZ (DMO) and 2-hydroxymethyl OLZ (2-OH-OLZ) (assessed by high-performance liquid chromatography) in 122 child and adolescent psychiatric patients (age 16.9 +/- 2.2, range, 10-21 years; 74 males, 48 females) with a variety of diagnoses: schizophrenia group (n = 80); nonschizophrenia group (n = 29); anorexia nervosa (AN) group (n = 13). Median OLZ serum concentrations were 32.7 (range, 1-118; all patients), 37.7 (2-115; schizophrenia group), and 18.7 (1-63, AN group) ng/mL. The median OLZ concentration-to-dose (C/D) ratio (n = 122) was 2.6, with 90% of the distribution between 0.8 and 5.5 (ng/mL)/(mg/d). OLZ concentration was significantly correlated with DMO (r = 0.567; P < 0.0005) but not with 2-OH-OLZ (r = 0.122; P = 0.188). Daily OLZ dose was correlated with OLZ concentration in all (r = 0.684; P < 0.0005), schizophrenic (r = 0.542; P < 0.0005), and AN (r = 0.805; P = 0.001) patients, respectively. Patients aged less than 16 years displayed similar C/D for OLZ (P = 0.58) but higher C/D for DMO (P = 0.003) than those 16 years or older. AN patients received lower median OLZ doses (7.5; 5-15 mg) than schizophrenic patients (12.5; 2.5-40 mg), even after correcting for body mass index (P = 0.02). OLZ dose did not differ (P = 0.088) between smokers and nonsmokers, but smokers showed lower C/D for OLZ than nonsmokers (P = 0.008). C/D for OLZ was 38% higher (P = 0.041) under comedication with selective serotonin reuptake inhibitors when compared with OLZ monotherapy. Multiple linear regression analysis revealed that 46% of the variation of OLZ concentration can be explained by dose, diagnosis, age, sex, smoking, and comedication. The data are compared with the literature, and the relevance of therapeutic antipsychotic drug monitoring in previously sparsely investigated subgroups, such as children and adolescents or patients with AN, is emphasized.

A prospective study of serum ghrelin levels in patients treated with clozapine

We investigated serum ghrelin levels (SGL) in 12 patients with schizophrenia over a 10-week period after initiation of clozapine treatment. In contrast to increments of body mass indices (BMI, kg/m2) and serum leptin levels (SLL), no significant change in SGL was detected. Inverse correlations between delta SGL and delta SLL did not reach statistical significance. Linear mixed model analysis could not detect effects of age, sex, BMI, SLL and serum clozapine levels on SGL. Our results do not support a causal involvement of ghrelin in clozapine-related weight gain.

Adsorptive stripping voltammetric quantification of the antipsychotic drug clozapine in bulk form, pharmaceutical formulation and human serum at a mercury electrode

Using the cyclic voltammetry technique and the Britton-Robinson buffer (pH 2-10) as a supporting electrolyte, clozapine was found to reduce at the hanging mercury drop electrode in a single two-electron irreversible step corresponding to reduction of the azomethine group of the seven-member heterocyclic ring. Based on the interfacial adsorptive character of clozapine onto the hanging mercury drop electrode, a validated square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure was described for the quantification of bulk clozapine with limits of detection and quantitation of 4.5 x 10(-10) and 1.5 x 10(-9) M, respectively. The proposed procedure was successfully applied to the quantification of the drug in pharmaceutical formulation (Leponex) and human serum without the necessity for samples' pretreatment or any time-consuming extraction or evaporation steps prior to the analysis. The limits of detection and quantitation of clozapine in spiked human serum were found to be 1 x 10(-9) and 3.3 x 10(-9) M, respectively. The proposed procedure for quantification of clozapine in bulk form, tablets and human serum has the advantage of being simple, rapid, sensitive, precise and inexpensive compared to most of the reported methods.

Pharmacokinetics of clozapine and its metabolites in hippocampal HT22 cells

Up to now, it is not yet clear whether and how clozapine and its metabolites are metabolized in neuronal cells. The interconversion of clozapine and its metabolites, clozapine-N-oxide and norclozapine, was studied in the hippocampal neuronal in vitro system of HT22 cells. Clinically relevant concentrations of clozapine (200+400 ng/ml) and its metabolites (100+200 ng/ml) were used for the examination of the metabolizing effects after short- (4 h) and long- (24 h) term incubation. Two-way analysis of variance revealed a significant decrease of clozapine (P<0.01) and norclozapine (P<0.01) levels in the supernatants of HT22 cells after the treatment procedures. Student-Newman-Keuls tests showed a significant decrease of clozapine 400 after 24 h of incubation (P=0.01) as well as of all concentrations of norclozapine. No significant treatment effects were found for the clozapine-N-oxide degradation. Using semi-quantification by reverse transcriptase-polymerase chain reaction methods, we could show a significant increase of cytochrome P450 (CYP) 1A2 mRNA levels (P<0.05) after clozapine treatment with 200 ng/ml. The results of the present study strongly suggest that clozapine and norclozapine are metabolized in hippocampal neuronal HT22 cells by CYP1A2, whereas the levels of clozapine-N-oxide were not affected. Moreover, CYP1A2 mRNA levels were significantly changed by incubation with clozapine 200.

Determination of clozapine, and its metabolites, N-desmethylclozapine and clozapine N-oxide in dog plasma using high-performance liquid chromatography

Clozapine and its two major metabolites, N-desmethylclozapine and clozapine N-oxide were quantified using a high-performance liquid chromatographic method with UV detection in dog plasma following a single dose of clozapine. The analysis was performed on a 5-micrometer Hypersil CN (CPS-1; 250x4.6 mm) column. The mobile phase consisted of acetonitrile-water-1 M ammonium acetate (50:49:1, v/v/v), which was adjusted to pH 5.0 with acetic acid. The detection wavelength was 254 nm. A liquid-liquid extraction technique was used to extract clozapine and its metabolites from dog plasma. The recovery rates for clozapine, N-desmethylclozapine, and the internal standard (I.S.) were close to 100% using this method. The recovery rate for clozapine N-oxide (62-66%) was lower as expected because it is more polar. The quantitation limits for clozapine, clozapine N-oxide, and N-desmethylclozapine were 0.11, 0.05 and 0.05 microM, respectively. Intra-day reproducibility for concentrations of 0.1, 1.0 and 5.0 microM were 10.0, 4.4 and 4.2%, respectively, for N-oxide; 11.2, 4.3 and 4.9%, respectively, for N-desmethylclozapine; and 10.8, 2.2 and 4.9%, respectively, for clozapine. Inter-day reproducibility was <15% for clozapine N-oxide, <8% for N-desmethylclozapine and <19% for clozapine. This simple method was applied to determine the plasma concentration profiles of clozapine, N-desmethylclozapine and clozapine N-oxide in dog following administration of a 10 mg/kg oral dose of clozapine.

Serotonergic effects of clozapine and its metabolites in hippocampal HT22 cells

In the hippocampal neuronal in vitro system of HT22 cells, we studied the effects of clozapine (Cloz) and its metabolites clozapine-N-oxide (Cloz-N-oxide) and norclozapine (Norcloz) on 5-HT transporter affinity (K(M)) and uptake (V(max)), MAO-B affinity (K(M)) and maximal velocity (V(max)), as well as on 5-HT(2) receptor affinity and density. Clinically relevant concentrations of Cloz (200 and 400 ng/ml) and its metabolites (100 and 200 ng/ml) were used for the examination of the effects after short-term (4 h) and long-term (24 h) incubation. Statistical evaluation revealed that a significantly lowered 5-HT transporter affinity (higher K(M)) was related to higher concentrations of Cloz and its metabolites. A significantly higher 5-HT transporter uptake was dependent on both high concentrations of drugs and an increased time of incubation. No significant influence of the investigated independent variables on MAO-B affinity could be demonstrated, whereas a significant drug-related increase of MAO-B velocity was detectable. Additionally, low and high concentrations of Cloz and its metabolites induced a higher 5-HT(2) receptor affinity (lower K(D)). No significant influences of the investigated independent variables on 5-HT(2) receptor density were detectable. The results of the present study show that Cloz and its metabolites induce significant alterations in serotoninergic parameters of hippocampal HT22 cells, validating the system of hippocampal HT22 cells for further examinations of the mechanisms of action of atypical neuroleptics.

Direct-injection high performance liquid chromatography ion trap mass spectrometry for the quantitative determination of olanzapine, clozapine and N-desmethylclozapine in human plasma

A specific and sensitive direct-injection high performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) method has been developed for the rapid identification and quantitative determination of olanzapine, clozapine, and N-desmethylclozapine in human plasma. After the addition of the internal standard dibenzepin and dilution with 0.1% formic acid, plasma samples were injected into the LC/MS/MS system. Proteins and other large biomolecules were removed during an online sample cleanup using an extraction column (1 x 50 mm i.d., 30 microm) with a 100% aqueous mobile phase at a flow rate of 4 mL/min. The extraction column was subsequently brought inline with the analytical column by automatic valve switching. Analytes were separated on a 5 microm Symmetry C18 (Waters) analytical column (3.0 x 150 mm) with a mobile phase of acetonitrile/0.1% formic acid (20:80, v/v) at a flow rate of 0.5 mL/min. The total analysis time was 6 min per sample. The inter- and intra-assay coefficients of variation for all compounds were <11%. By eliminating the need for extensive sample preparation, the proposed method offers very large savings in total analysis time.

Simultaneous determination of olanzapine, clozapine and demethylated metabolites in serum by on-line column-switching high-performance liquid chromatography

An automated method for simultaneous routine quantification of the antipsychotic drugs clozapine, olanzapine and their demethylated metabolites is described. The method included adsorption on a cyanopropyl (CPS) coated clean-up column (10 microm; 10 x 2.0 mm I.D.), washing off interfering serum constituents to waste, and separation on C18 ODS Hypersil reversed phase material (5 microm; 250 x 4.6 mm I.D.) using acetonitrile-water-tetramethylethylenediamine (37:62.6:0.4, v/v/v) adjusted to pH 6.5 with concentrated acetic acid. UV-detection was performed at 254 nm. The limit of quantification was 10-20 ng/ml. Relative day to day standard variations ranged between 4.5 and 13.5%. The method is suitable for routine monitoring of olanzapine and clozapine including their demethylated metabolites.

Rapid capillary electrophoretic method for the determination of clozapine and desmethylclozapine in human plasma

A rapid and sensitive high-performance capillary electrophoretic method for the determination of clozapine and its main metabolite desmethylclozapine in human plasma was developed. The separation of the two analytes was carried out in an untreated fused-silica capillary [33 cm (8.5 cm effective length) x 50 microm I.D.] filled with a background electrolyte at pH 2.5 containing beta-cyclodextrin. Baseline separation of clozapine and desmethylclozapine was recorded in less than 3 min. An accurate sample pretreatment by means of solid-phase extraction and subsequent concentration allows for reliable quantitation of clozapine in the plasma of schizophrenic patients under treatment with the drug. The method showed good precision (mean RSD = 4.0%) as well as satisfactory extraction yields (approximately 88%) and a good sensitivity (limit of quantitation = 0.075 microg ml(-1), limit of detection = 0.025 microg ml(-1)).

Atypical neuroleptics in child and adolescent psychiatry

Atypical neuroleptics have enriched our treatment programmes, especially in childhood and adolescent schizophrenia. This article reviews the use of atypical neuroleptics in children and adolescents with schizophrenic disorder. It considers the receptor binding profile and pharmacological properties, indications, side effects, clinical applications and trials of atypical neuroleptics in comparison to the classical neuroleptic haloperidol in adolescent schizophrenia. Special emphasis is placed on the most common atypical neuroleptics clozapine, olanzapine and risperidone since most studies are carried out with these compounds, especially with clozapine. More clinically controlled trials have to be conducted since only one was performed so far. The place of the atypical neuroleptics is discussed and further studies are necessary in order to differentiate the indications tested so far and to find out if the spectrum of indications can be broadened.

Atypische Neuroleptika in der Kinder- und Jugendpsychiatrie

Zusammenfassung: Atypische Neuroleptika haben unsere Therapiemöglichkeiten in der Kinder- und Jugendpsychiatrie verbessert. Dieser Artikel faßt die Anwendung der atypischen Neuroleptika bei Kindern und Jugendlichen mit schizophrenen Psychosen zusammen. Es werden das Rezeptor-Bindungsprofil, pharmakologische Eigenschaften, Indikationen, Nebenwirkungen, klinische Anwendungen und Studien der atypischen Neuroleptika, im Vergleich zu dem klassischen Neuroleptikum Haloperidol, berücksichtigt. Besondere Betonung wurde auf die am häufigsten verwendeten atypischen Neuroleptika Clozapin, Olanzapin und Risperidon gelegt, da weltweit die meisten Studien mit diesen Medikamenten durchgeführt worden sind. Der Stellenwert der atypischen Neuroleptika wird diskutiert und es werden weitere Studien gefordert, um die Indikationen zu differenzieren, und um zu sehen, ob das Indikationsspektrum erweitert werden kann.

Separation of antipsychotic drugs (clozapine, loxapine) and their metabolites by capillary zone electrophoresis

Two antipsychotic drugs (clozapine and loxapine) and six metabolites, N-demethylclozapine, clozapine N-oxide, N-demethylloxapine (amoxapine), 7-hydroxyloxapine, 8-hydroxyloxapine, 8-hydroxyamoxapine, were separated by capillary zone electrophoresis. Variation of pH and ionic strength of the acidic phosphate buffer (pH below 4) did not enable the separation of loxapine and one of its metabolites. Resolution of the single parent drugs and their metabolites was possible in background electrolytes (phosphate, pH 3.5, 60 mmol/l) containing either 0.2% (w/v) polyvinylpyrrolidone as replaceable pseudo-stationary phase, or 0.75 mmol/l beta-cyclodextrin added as complex-forming agent. Full separation of the mixture with baseline resolution of all analytes was obtained with a background electrolyte with heptakis-6-sulfato-beta-cyclodextrin added as negatively charged complexation agent with improved separation selectivity.

Blood biogenic amines during clozapine treatment of early-onset schizophrenia

The aims of this investigation were to evaluate long-term and short-term effects of clozapine-treatment on plasma biogenic amines and psychopathology measures in adolescents with schizophrenia (DSM-III-R criteria). The long-term study was conducted in a study sample of 40 young patients (age 14-22 years) following a mean of 3.4 years of neuroleptic treatment. During the study, 20 patients received clozapine, and the other 20 patients were treated with standard neuroleptic medications. At the beginning of the open clinical trials, the patients had already been receiving clozapine treatment for 24 +/- 15 months. Assessment of the biochemical and psychopathological measures was performed on six occasions at consecutive 6-week intervals during maintenance treatment with clozapine or conventional neuroleptics. Blood levels of serotonin, 3-methoxy-4-hydroxy-phenylglycol (MHPG), norepinephrine, and epinephrine were significantly higher in clozapine-treated patients than in conventionally treated patients. During long-term treatment, higher serotonin levels were associated with significantly fewer negative symptoms of schizophrenia, whereas higher MHPG levels were correlated with less depression. The short-term effects of clozapine were assessed in a second and independent study sample. After failing on conventional neuroleptics in clinical trials lasting a mean of 1.6 years, 15 inpatients (aged 11-20 years) received clozapine. Weekly ratings of psychopathological symptoms using standard rating scales were performed in parallel to blood samplings for measurements of biogenic amines and serum levels of clozapine. These measures were obtained for 6 weeks during conventional neuroleptic treatment and for 6 weeks during the open-label clozapine trial. Serum levels of serotonin and plasma norepinephrine levels were significantly higher during treatment with clozapine than during pretreatment with typical neuroleptics. A comparison of plasma epinephrine levels in responders (n = 7) and nonresponders (n = 8) to clozapine revealed that response to clozapine can be predicted by epinephrine levels prior to initiation of treatment with clozapine (responders ranging from 32.2 to 90.3 pg/ml; nonresponders ranging from 92.5 to 473.5 pg/ml). Additionally, subjects who responded to clozapine showed increased mean plasma concentrations of MHPG and epinephrine during treatment with this drug in comparison to the levels measured during pretreatment with typical neuroleptic medication. Nonresponders to clozapine failed to show this increase. Finally, in responders to clozapine a negative linear relationship between negative symptoms of schizophrenia and the concentrations of plasma norepinephrine and serum serotonin were observed. In conclusion, our results demonstrate that plasma epinephrine levels prior to initiation of clozapine therapy predict response to this atypical neuroleptic. Our findings derived from short-term and maintenance treatment with clozapine suggest involvement of norepinephrine, epinephrine and serotonin in the therapeutic actions of the atypical neuroleptic clozapine.

Automated determination of clozapine and major metabolites in serum and urine

Clozapine is an atypical neuroleptic that is increasingly used for the treatment of schizophrenia. An automated method was developed for the routine quantification of clozapine and its major metabolites, N-desmethylclozapine and clozapine N-oxide, in human serum and urine by column switching and online high-performance liquid chromatography with ultraviolet detection. The method included adsorption of clozapine and its metabolites on a cyanopropyl-coated clean-up column (10 microns; 10 mm x 4.0 mm ID), washing interfering serum constituents to waste by deionized water, and, after column switching, separation on C18 ODS Hypersil reversed-phase material (5 microns; 250 mm x 4.6 mm ID). The compounds of interest were separated and eluted in fewer than 20 minutes, using a mobile phase consisting of 37.5 acetonitril:62.5 water, containing 0.4% (vol/vol) tetramethylethylenediamine and adjusted to pH 6.5 with concentrated acetic acid. Ultraviolet-detection was performed at 254 nm. The determinations exhibited linearity between detector signal and drug concentrations in a range from 5 ng/ml to 50 micrograms/ml. As little as 10 ng/ml of clozapine and 20 or 30 ng/ml of the metabolites was quantifiable. Interferences with other psychotropic drugs, serum, or urine constituents were negligible. The automated procedure enables the analysis of clozapine and metabolites in serum or urine in less than 1 hour.

Fatal overdose of clozapine

An ingestion of an unknown quantity of Leponex (clozapine) tablets in a suicide is described. Although clozapine is known for over 30 years now, relatively few cases of intoxications due to clozapine overdose have been reported. The authors report a new and quick method to analyze and determine the clozapine and N-desmethylclozapine concentration in body fluids. The analytes and an internal standard (zolpidem) were extracted from alkalinized samples into ethyl acetate before GC/NPD analysis. The proposed method resulted in a rapid procedure most useful in cases of deliberate poisoning with the neuroleptic drug Leponex.