Haloperidol and reduced haloperidol serum levels: correlation with psychopathology in acute schizophrenia

Automated Interlaboratory Comparison of Therapeutic Drug Monitoring Data and Its Use for Evaluation of Published Therapeutic Reference Ranges

Therapeutic drug monitoring is a tool for optimising the pharmacological treatment of diseases where the therapeutic effect is difficult to measure or monitor. Therapeutic reference ranges and dose-effect relation are the main requirements for this drug titration tool. Defining and updating therapeutic reference ranges are difficult, and there is no standardised method for the calculation and clinical qualification of these. The study presents a basic model for validating and selecting routine laboratory data. The programmed algorithm was applied on data sets of antidepressants and antipsychotics from three public hospitals in Denmark. Therapeutic analytical ranges were compared with the published therapeutic reference ranges by the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) and in additional literature. For most of the drugs, the calculated therapeutic analytical ranges showed good concordance between the laboratories and to published therapeutic reference ranges. The exceptions were flupentixol, haloperidol, paroxetine, perphenazine, and venlafaxine + o-desmethyl-venlafaxine (total plasma concentration), where the range was considerably higher for the laboratory data, while the calculated range of desipramine, sertraline, ziprasidone, and zuclopenthixol was considerably lower. In most cases, we identified additional literature supporting our data, highlighting the need of a critical re-examination of current therapeutic reference ranges in Denmark. An automated approach can aid in the evaluation of current and future therapeutic reference ranges by providing additional information based on big data from multiple laboratories.

ABCB1 and CYP2D6 polymorphisms and treatment response of psychotic patients in a naturalistic setting

OBJECTIVES

The aim of our study was to examine the association between ABCB1 polymorphisms G2677T/A (rs2032582) and C3435T (rs1045642) and common CYP2D6 variants, with the response to antipsychotic treatment of psychotic patients, in a naturalistic setting, in Greece.

METHODS

One hundred patients suffering from schizophrenia and other psychotic disorders were included in the study. Dosages were normalized to chlorpromazine equivalents. Response following 1 month of treatment was assessed as either a continuous variable, using the distribution of the corrected Positive and Negative Syndrome Scale percent change, or as a dichotomous variable defined as the number of patients scoring ≥30% from the corrected baseline Positive and Negative Syndrome Scale score. Genotyping was achieved with established polymerase chain reaction-restriction fragment length polymorphism methods.

RESULTS

With response treated as a continuous variable, the homozygous recessive rs2032582 genotypes (TT) who were simultaneously carriers of a loss-of-function CYP2D6 allele (*4 or *5) responded significantly worse than the rest of the patients. Comparison of genotype frequencies revealed a statistically significant association of the above combination. No significant association between chlorpromazine equivalents and the tested genotypes was detected.

CONCLUSION

We have detected a possible interaction between ABCB1 and CYP2D6 in affecting response of psychotic patients to drug treatment, in a naturalistic setting.

Mechanisms of action of antipsychotic drugs of different classes, refractoriness to therapeutic effects of classical neuroleptics, and individual variation in sensitivity to their actions: Part II

Rapid-onset psychotic rebound is uncommon on discontinuation of most antipsychotic drugs, as might be expected for antipsychotic drugs with (hypothetically) indirect actions at their final target receptors. Rapid-onset psychosis is more common on withdrawal of clozapine, which might be expected if its action is direct. Drugs other than clozapine (notably thioridazine) may have hitherto unrecognised similarities to clozapine (but without danger of agranulocytosis), and may be useful in treatment of refractory psychosis. Quetiapine fulfils only some criteria for a clozapine-like drug. Clinical response to neuroleptics varies widely at any given plasma level. Haase's "neuroleptic threshold" concept suggests that the dose producing the slightest motor side effects produces most or all of the therapeutic benefit, but analyses presented here suggest that antipsychotic actions are not subject to a sharp "all-or-none" threshold but increase over a small dose range. This concept could provide a method for quantitative determination of individualized optimal doses.

Haloperidol plasma concentration in Japanese psychiatric subjects with gene duplication of CYP2D6

AIMS

The cytochrome P-450 2D6 (CYP2D6) gene duplication/multiduplication producing an increase in enzyme activity, and the common Japanese mutation, CYP2D6*10A producing a decrease of enzyme activity were screened in a large number of Japanese psychiatric subjects (n = 111) in order to investigate whether these mutated alleles affected the plasma concentration of haloperidol.

METHODS

Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was performed to identify the CYP2D6*10A and CYP2D6*2 genotypes in subjects who had been taking haloperidol. For the screening of duplicated active CYP2D6 gene, allele-specific long PCR was performed. Plasma concentration of haloperidol was measured by the enzyme immunoassay, and expressed as "plasma concentration dose ratio" to normalize individual differences.

RESULTS

The plasma concentration-dose ratio showed large interindividual differences of approximately 18-fold. PCR-RFLP methods revealed that 29 (26.1%), 10 (9.0%), 39 (35.1%), 0 (0%), seven (6.3%) and 26 (23.4%) cases possessed the CYP2D6 genotypes *1/*1, *1/*2, *1/*10A, *2/*2, *2/*10A and *10 A/*10A, respectively. Six cases (5.4%) had duplicated CYP2D6 genes. There were no significant differences of plasma concentration-dose ratio between the groups classified by CYP2D6*10A and *2 genotypes (Kruskal-Wallis test; P = 0.37), even in those cases whose daily doses were lower than 20 mg (n = 90, P = 0.91). Subjects having duplicated genes (n = 6) did not show significant differences of plasma concentration-dose ratio by comparison with subjects who had no duplicated genes (Mann-Whitney U-test; P = 0.80).

CONCLUSIONS

Gene duplication, and the common Japanese mutation CYP2D6*10A on CYP2D6 gene are not likely to be the main modulatory factors of plasma concentration of haloperidol in Japanese psychiatric subjects.

Disposition of haloperidol pyridinium and reduced haloperidol pyridinium in schizophrenic patients: no relationship with clinical variables during short-term treatment

In an open clinical trial, serum concentrations of haloperidol pyridinium (C(HP+)) and reduced haloperidol pyridinium (C(RHP+)), as well as haloperidol (CH) and reduced haloperidol (C(RH)), were measured in 57 schizophrenic and schizoaffective inpatients during 6 weeks of short-term treatment. Psychopathology was monitored with the Brief Psychiatric Rating Scale (BPRS), and extrapyramidal adverse effects were assessed with the Extrapyramidal Symptom Rating Scale (EPS). Significantly linear relationships were found between haloperidol dose (D) and pyridinium metabolite serum concentrations, as well as between C(H) and the pyridinium metabolite serum concentrations. C(HP+) (range, 0.2-4.9 ng/mL) and C(RHP+) (range, 0.03-6.23 ng/mL) were low compared with C(H) and C(RH), being as mean values approximately 7% and 14% of C(H) and C(RH), respectively. Additionally, the values of C(RHP+) and the slope of the correlation of C(H) with the C(RHP+)/C(HP+) ratio were considerably lower than in a previous report of long-term treatment with haloperidol. This is explained by the shorter time of treatment of the present study. Carbamazepine comedication was found to not influence relative pyridinium metabolite serum concentrations C(HP+)/D and C(RHP+)/D. However, the aromatization ratios of haloperidol (C(HP+)/C(H)) and reduced haloperidol (C(RHP+)/C(RH)) were increased by concomitant carbamazepine. As the main result, no relationships between the pyridinium metabolite serum concentrations and clinical variables (BPRS change, EPS, dose of biperiden) were detected. For instance, the aromatization ratios C(HP+)/C(H) and C(RHP+)/C(RH) did not predict clinical improvement or extrapyramidal adverse effects. Therefore, no confirmation of the "pyridinium hypothesis," which suggests haloperidol pyridinium metabolites to be the origin of adverse effects and decreased therapeutic effect, can be derived from this study. However, the authors emphasize that pyridinium metabolites cannot be excluded as the origin of decreased therapeutic effect in long-term treatment and of adverse effects not investigated in the present study, such as tardive dyskinesia. Finally, it is concluded that the serum concentration of the parent drug remains the main variable of interest in the therapeutic drug monitoring of haloperidol during short-term treatment.

The relationship between serum concentration and therapeutic effect of haloperidol in patients with acute schizophrenia

Haloperidol is the most commonly used antipsychotic drug in the therapy of acute schizophrenia. Clinicians have been using therapeutic drug monitoring in an attempt to improve clinical application of this drug. The scale of interest in this area is emphasised by the large number of studies (about 50) concerning the serum concentration-therapeutic effect relationship (SCTER) of haloperidol, including 35 studies on patients with acute schizophrenia. However, conflicting results concerning the existence and position of a therapeutic window have emerged. This article aims to provide a comprehensive review of the study design of studies in patients with acute schizophrenia before the study data are used for decision-making. For this purpose, a reproducible system for the evaluation of studies in this special area, a so-called total study score (TSS), was developed on an empirical basis. Thus, insufficient study design was found to be a reason for negative results. On the other hand, in spite of a great variability, the majority of studies with good design provided evidence for a significant SCTER: a bisigmoidal dependence of clinical effect on haloperidol serum concentration. The therapeutic effects of haloperidol increase at low concentrations, and the concentration has a maximum effect at about 10 micrograms/L and again decreasing at higher concentrations. The data of 552 patients also fit to this model in a single scatter plot (pseudo-r2 = 0.076, p < 0.001). The position of the therapeutic window was determined at about 5.6 to 16.9 micrograms/L. Patients treated with serum concentrations within this optimal range had a significantly better response compared with outside this range (p < 0.001, Student t-test). Therefore, a quantitative synthesis of all available data by means of effect-size analysis provides a mean effect-size (g) = 0.499 +/- 0.182 (standard deviation) for the comparison of haloperidol-treatment with serum concentrations within versus outside the therapeutic window. Thus, because of this moderate positive effect, serum concentration assay of haloperidol is recommended for patients with acute schizophrenia in a therapeutic drug monitoring programme. The modalities of haloperidol therapeutic drug monitoring in clinical practice are discussed, e.g. patient selection, method and time for serum concentration measurement, influence of premedication and comedication, interpretation of results and dose adjustment. Clinical investigations into this subject should focus on covariates which are responsible for the variability of the SCTER. Serum concentration assay is advised for investigations of nonresponse to exclude patients with pseudo-drug resistance.

Megabore capillary gas-liquid chromatographic method with nitrogen-phosphorus selective detection for the assay of haloperidol and reduced haloperidol in serum: results of therapeutic drug-monitoring during acute therapy of eight schizophrenics

A gas chromatographic method using a HP-5 megabore capillary and nitrogen-phosphorus selective detection for the quantitative analysis of haloperidol (H) and reduced haloperidol (RH) in human serum or plasma is described. A 3-step liquid-liquid extraction is applied. The extraction yield of this procedure is 63% for haloperidol at 20 ng/ml. The limits of detection are 0.4 ng/ml for haloperidol and 1.0 ng/ml for the metabolite if 2 ml of body fluid are applied. At 10 ng/ml the within-day precision is 4.5% for H and 8.3% for RH. Serum levels of eight schizophrenic patients have been monitored weekly over a therapeutic period of six weeks. Seven patients mainly had metabolite ratios RH/H < 1 over the entire period of investigation. They exhibited a linear correlation between dose and serum concentration of haloperidol. In contrast, one patient had metabolite ratios RH/H > 1 over the entire period of the study. Due to considerable increased serum concentrations this patient did not show a linear correlation between the dose and the serum level of haloperidol.