Determination of Clozapine and Its Two Major Metabolites in Human Serum by Liquid Chromatography Using Ultraviolet Detection

Piperazine derivatives as dangerous abused compounds

Piperazine derivatives are a group of compounds with a psychostimulant effect. They are an alternative to illegal drugs. They are being searched for recreational use due to their psychoactive and hallucinogenic effects. The high popularity of these compounds can be noticed all over the world due to easy purchase, lack of legal regulations and incorrect assessment of the safety of use. The recreational use of piperazine derivatives can often result in chronic and acute health problems and additionally with unpredictable remote effects. It is also common to take mixtures of psychoactive compounds. This hinders the correct diagnosis and treatment of patients with poisoning. The presented work is an illustration of the wide problem of piperazine derivatives abuse. The health effects and the possibility of identifying these compounds in preparations and biological material are described.

Population Pharmacokinetics of Clozapine and Norclozapine and Switchability Assessment between Brands in Uruguayan Patients with Schizophrenia

Clozapine (CZP) is an atypical antipsychotic agent commonly used in the treatment of schizophrenia. It is metabolized primarily by CYP1A2 enzyme, yielding a pharmacologically active metabolite, norclozapine (NCZP). Significant intra- and interindividual pharmacokinetic (PK) variability for CZP and NCZP has been observed in routine therapeutic drug monitoring. So the goal of this study was to evaluate the magnitude and variability of concentration exposure to CZP and its active metabolite NCZP on pharmacokinetic parameters in Uruguayan patients with schizophrenia with a focus on covariates such as cigarette smoking, age, sex, caffeine consumption, brands available of CZP, and comedication using population PK (PPK) modeling methodologies. Patients with a diagnosis of schizophrenia treated with brand-name CZP (Leponex®) for more than a year were included in the study. Then these patients were switched to the similar brand of CZP (Luverina®). Morning predose blood samples for determination of CZP and NCZP using a HPLC system equipped with a UV detector were withdrawn on both occasions at steady state and under the same comedication. Ninety-eight patients, 22 women and 76 men, took part in the study. Mean ± standard deviation for CZP and NCZP concentration was 421 ± 262 ng/mL and 275 ± 180 ng/mL, respectively. After covariate evaluation, only smoking status remained significant in CZP apparent clearance, inducing a mean increment of 32% but with no clinical impact. The results obtained with the two brands of CZP should ensure comparable efficacy and tolerability with the clinical use of either product. Smoking was significantly associated with a lower exposure to CZP due to higher clearance. The results obtained with the two brands commercialized in our country hint a bioequivalence scenario in the clinical setting.

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.

Stability indicating methods for the determination of clozapine

Five new selective, precise and accurate methods are described for the determination of clozapine in the presence of its main degradation product. Method A utilizes the second and third derivative spectrophotometry at 315 and 305 nm, respectively. Method B is RSD(1) spectrophotometric method based on the simultaneous use of the first derivative of ratio spectra and measurement at 295 nm. Method C is a pH-induced difference (delta A) spectrophotometry using UV measurement at 325 nm. Method D is a densitometric one, after separation on silica gel plate using methanol: water as mobile phase, and the spot was scanned at 295 nm. Method E is RP-HPLC using acetonitrile: water (40:60 v/v) as mobile phase at a flow rate of 1 ml/min and UV detection was at 295 nm. Regression analysis showed good correlation in the concentration ranges 3-10, 4-10, 10-25 micro g/ml, 200-1000 ng/spot, 5-100 micro g/ml with percentage recoveries of 99.4+/-0.28, 99.8+/-0.20, 100.05+/-0.11, 99.41+/-0.34, 100.11+/-0.07 and 100.07+/-0.05% for methods A, B, C, D and E, respectively. These methods are suitable as stability indicating methods for the determination of clozapine in the presence of its main degradation product either in bulk powder or in pharmaceutical formulations.

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)).

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.

Determination of clozapine and its metabolite, N-desmethylclozapine, in serum microsamples by high-performance liquid chromatography and its application to pharmacokinetics in rats

A single solvent extraction step high-performance liquid chromatographic method is described for quantitating clozapine and its metabolite, N-desmethylclozapine, in rat serum microsamples (50 microl). The separation used a 2.1-mm I.D. reversed-phase Symmetry C18 column with an isocratic mobile phase consisting of methanol-acetonitrile-28.6 mM sodium acetate buffer, pH 2.6 (10:20:70, v/v/v). The detection limit was 2.5 ng/ml for all the compounds using an ultraviolet detector operated at 230 nm. The method was used to study the pharmacokinetics of clozapine after an intravenous bolus dose (2.5 mg/kg).