Possible levomepromazine-clozapine interaction: two case reports

Letter to the FDA Proposing Major Changes in the US Clozapine Package Insert Supported by Clozapine Experts Worldwide. Part I: A Review of the Pharmacokinetic Literature and Proposed Changes

PURPOSE/BACKGROUND

Clozapine was approved in the United States (US) using 1989 regulations and knowledge. After 30 years, many sections of the US package insert (PI) are outdated.

METHODS

We comprehensively reviewed the literature to propose PI updates. We present the information in 2 articles. In Part I, we focus on basic pharmacology based on 407 relevant articles. Part II focuses on clinical aspects and pharmacovigilance.

FINDINGS/RESULTS

Based on more recent expectations of Food and Drug Administration regulations, we reviewed clozapine basic pharmacology including the following: 1) clearance, 2) pharmacokinetics and pharmacodynamics, and 3) monitoring tools. We identified 9 major problems in the basic pharmacological sections of the PI including the following: 1) in vivo studies indicate that clozapine is dependent on CYP1A2 for its metabolism, 2) the minor role of CYP2D6 in clozapine metabolism requires removing the PI recommendation to lower clozapine doses in CYP2D6 poor metabolizers, 3) in nontoxic concentrations CYP3A4 has a minor role in clozapine metabolism and potent CYP3A4 inhibitors lack clinically relevant effects, 4) several drug-drug interactions need to be updated based on recent literature, 5) systemic inflammation may decrease clozapine metabolism and increase the risk of clozapine intoxication, 6) obesity may decrease clozapine metabolism, 7) patients of Asian and Indigenous American ancestry need lower clozapine doses, 8) personalized titration and c-reactive protein monitoring should be considered until prospective studies are available, and 9) the half-life section needs to be modified to acknowledge that single dosing at night is frequent in the US.

IMPLICATIONS/CONCLUSIONS

An improvement in the US clozapine PI may lead to improvement in PIs worldwide.

The effects of clinical and pharmacological factors on the ratio of clozapine to norclozapine in psychiatric patients

Background

Due to its exceptional effectiveness, clozapine (CLO), whose metabolite is norclozapine (NCLO), is a drug of choice in the management of treatment-resistant schizophrenia. The purpose of this study was to assess the factors modifying the CLO/NCLO ratio (CNR).

Methods

A total of 446 blood samples (233 of which were drawn from females and 213 from males, aged from 18 to 77 years) were analyzed in this study. The patients were treated at a psychiatric hospital in the period 2016-2021. Serum CLO and NCLO levels were determined with high-performance liquid chromatography coupled with a UV detector.

Results

The median CNR was 2.38 (minimum 0.30, maximum 14.36). Our analysis showed that neither sex (p= 0.135) nor smoking (p = 0.774) had any significant effect on the CNR. However, increased doses of CLO resulted in lower CNR values (p = 0.005). Concomitant use of other psychotropic drugs increased the CNR (p = 0.001).

Discussion

The results of our study indicate a need for personalized CLO treatment. Assessing the CNR may be useful in identifying CLO interaction with other psychotropic drugs.

European Whites May Need Lower Minimum Therapeutic Clozapine Doses Than Those Customarily Proposed

PURPOSE/BACKGROUND

A nomogram from a British naturalistic study proposed that the clozapine dosing needed to reach a serum concentration of 350 ng/mL ranged from 265 mg/d (female nonsmokers) to 525 mg/d (male smokers). Some European reviews have used these dosing recommendations, which seem greater than what we found in an Italian White sample ranging from 245 mg/d (female nonsmokers) to 299 mg/d (male smokers). Five other published samples of European Whites were added to the Italian sample to estimate clozapine doses recommended for reaching 350 ng/mL.

METHODS/PROCEDURES

Average clozapine metabolizers were obtained by eliminating outliers with confounding variables: (1) psychiatric inducers and inhibitors; (2) doses less than 100 mg/d; and (3) when possible, patients with inflammation, obesity, or using oral contraceptives. The study included 1363 average metabolizer European Whites: the Italian sample and 5 new samples. Mean averages that reached serum concentration levels of 350 ng/mL were calculated after stratification by sex and smoking status in each sample. Then, weighted mean averages were obtained by combining the 6 samples.

FINDINGS/RESULTS

The estimated weighted mean clozapine dosages ranged from 236 to 368 mg/d (236 mg/d in 218 female nonsmokers, 256 mg/d in 340 male nonsmokers, 357 mg/d in 269 female smokers, and 368 mg/d in 546 male smokers).

IMPLICATIONS/CONCLUSIONS

Our recommended dosages are less than those recommended in Europe. Future studies in European Whites need to replicate these recommended doses for average metabolizer patients after sex and smoking stratification and further explore clozapine dosing for those with relevant clinical confounders.

Levomepromazine and clozapine induce the main human cytochrome P450 drug metabolizing enzyme CYP3A4

Background

Cytochrome P450 (CYP) enzymes are involved in the metabolism of many important endogenous substrates (steroids, melatonin), drugs and toxic xenobiotics. Their induction accelerates drug metabolism and elimination. The present study aimed at examining the inducing abilities of two antipsychotic drugs levomepromazine and clozapine for the main CYPs.

Methods

The experiments were performed using cryopreserved human hepatocytes. The hepatotoxicity of levomepromazine and clozapine was assessed after exposure to the neuroleptics (LDH test). CYP activities were measured in the incubation medium using the CYP-specific reactions: caffeine 3-N-demethylation (CYP1A1/2), diclofenac 4′-hydroxylation (CYP2C9), perazine N-demethylation (CYP2C19) and testosterone 6β-hydroxylation (CYP3A4). In parallel, CYP mRNA levels were measured in neuroleptic-treated hepatocytes.

Results

The results indicate that levomepromazine and clozapine induce the expression of main CYP enzyme CYP3A4 in human hepatocytes. Levomepromazine and clozapine at concentrations of 2.5 and 10 µM, respectively, caused a significant increase in the mRNA level and activity of CYP3A4. Both neuroleptics did not produce any changes in CYP1A1/2, CYP2C9 and CYP2C19.

Conclusion

Levomepromazine and clozapine induce CYP3A4 in human hepatocytes in vitro. Further in vivo studies are advisable to confirm the CYP3A4 induction by levomepromazine and clozapine in the liver, and to assess the effect of these drugs on their own metabolism and on the biotransformation of other co-administered drugs which are the CYP3A4 substrates.

Meet the relatives: a reintroduction to the clinical pharmacology of ‘typical’ antipsychotics (Part 1)

A number of pragmatic trials have cast doubt on the concept of ‘atypicality’ in relation to antipsychotic drugs, and some commentators have argued that the dichotomy between ‘typical’ (‘first-generation’) and ‘atypical’ ('second-generation’) compounds is artificial and should be abandoned, leaving the entire class of antipsychotics available for consideration in more individualised treatment planning. However, younger psychiatrists now gain little or no experience in the use of older antipsychotics. This is the first of two articles addressing practical issues for consideration in prescribing the older antipsychotics available in the UK. It covers background, including the fundamental clinical action of antipsychotics, the nature of drug licensing and identification of pharmacological parameters that may be of value in prescribing decisions, and discusses the phenothiazines: chlorpromazine, promazine, levomepromazine, pericyazine, perphenazine, trifluoperazine and prochlorperazine.

A reliable and rapid tool for plasma quantification of 18 psychotropic drugs by ESI tandem mass spectrometry

A simple liquid chromatographic tandem mass spectrometry (LC-MS/MS) method has been developed for simultaneous analysis of 17 basic and one acid psychotropic drugs in human plasma. The method relies on a protein precipitation step for sample preparation and offers high sensitivity, wide linearity without interferences from endogenous matrix components. Chromatography was run on a reversed-phase column with an acetonitrile-H₂O mixture. The quantification of target compounds was performed in multiple reaction monitoring (MRM) and by switching the ionization polarity within the analytical run. A further sensitivity increase was obtained by implementing the functionality "scheduled multiple reaction monitoring" (sMRM) offered by the recent version of the software package managing the instrument. The overall injection interval was less than 5.5 min. Regression coefficients of the calibration curves and limits of quantification (LOQ) showed a good coverage of over-therapeutic, therapeutic and sub-therapeutic ranges. Recovery rates, measured as percentage of recovery of spiked plasma samples, were ≥ 94%. Precision and accuracy data have been satisfactory for a therapeutic drug monitoring (TDM) service as for managing plasma samples from patients receiving psycho-pharmacological treatment.

ABCB1 and cytochrome P450 polymorphisms: clinical pharmacogenetics of clozapine

To examine the genetic factors influencing clozapine kinetics in vivo, 75 patients treated with clozapine were genotyped for CYPs and ABCB1 polymorphisms and phenotyped for CYP1A2 and CYP3A activity. CYP1A2 activity and dose-corrected trough steady-state plasma concentrations of clozapine correlated significantly (r = -0.61; P = 1 x 10), with no influence of the CYP1A2*1F genotype (P = 0.38). CYP2C19 poor metabolizers (*2/*2 genotype) had 2.3-fold higher (P = 0.036) clozapine concentrations than the extensive metabolizers (non-*2/*2). In patients comedicated with fluvoxamine, a strong CYP1A2 inhibitor, clozapine and norclozapine concentrations correlate with CYP3A activity (r = 0.44, P = 0.075; r = 0.63, P = 0.007, respectively). Carriers of the ABCB1 3435TT genotype had a 1.6-fold higher clozapine plasma concentrations than noncarriers (P = 0.046). In conclusion, this study has shown for the first time a significant in vivo role of CYP2C19 and the P-gp transporter in the pharmacokinetics of clozapine. CYP1A2 is the main CYP isoform involved in clozapine metabolism, with CYP2C19 contributing moderately, and CYP3A4 contributing only in patients with reduced CYP1A2 activity. In addition, ABCB1, but not CYP2B6, CYP2C9, CYP2D6, CYP3A5, nor CYP3A7 polymorphisms, influence clozapine pharmacokinetics.

Simultaneous analysis of classical neuroleptics, atypical antipsychotics and their metabolites in human plasma

A high-performance liquid chromatographic method has been developed for the simultaneous determination of classical neuroleptics (chlorpromazine, haloperidol, loxapine and clotiapine), atypical antipsychotics (clozapine, quetiapine and risperidone) and their active metabolites (N-desmethylclozapine, clozapine N-oxide and 9-hydroxyrisperidone) in human plasma. Separation was obtained by using a C8 reversed-phase column and a mobile phase composed of 70% aqueous phosphate buffer containing triethylamine at pH 3.0 and 30% acetonitrile. The UV detector was set at 238 nm and amitriptyline was used as the internal standard. A careful pre-treatment procedure of plasma samples was developed, using solid-phase extraction with cyanopropyl cartridges, which gives high extraction yields (>or=93%). The limits of quantitation (LOQ) were always lower than 2.6 ng mL-1 and the limits of detection (LOD) were always lower than 0.9 ng mL-1 for all analytes. The method was applied with success to plasma samples from schizophrenic patients undergoing polypharmacy with two or more different antipsychotics. Precision data and accuracy results were satisfactory and no interference from other central nervous system (CNS) drugs was found. Hence the method is suitable for the therapeutic drug monitoring (TDM) of the analytes in psychotic patients' plasma.