Alfredo de la Rubia

QTc interval lengthening is related to CYP2D6 hydroxylation capacity and plasma concentration of thioridazine in patients

Thioridazine cardiotoxicity has been associated with a prolonged heart-rate corrected QT (QTc) interval. However, no systematic studies have been performed on patients at therapeutic doses. The present study aimed to evaluate the influence of dose and plasma concentration of thioridazine and CYP2D6 enzyme status on the QTc interval in psychiatric patients. Sixty-five Spanish European psychiatric patients receiving thioridazine antipsychotic monotherapy were studied. The plasma levels of thioridazine and its metabolites were determined by high-performance liquid chromatography. All patients were phenotyped for CYP2D6 activity with debrisoquine during treatment. Thirty-five patients (54%) had a QTc interval over 420 ms. The lengthening of QTc interval was correlated with plasma concentration (p< 0.05) and daily dose (p < 0.05) of thioridazine. CYP2D6 enzyme hydroxylation capacity, evaluated by debrisoquine metabolic ratio (MR) (p < 0.05) and thioridazine/mesoridazine ratio (p < 0.05), was also correlated with QTc intervals. The present study shows the relationship between QTc interval lengthening among psychiatric patients treated at therapeutical doses with the dose and the plasma concentration of thioridazine. Since debrisoquine MR has been shown to be correlated with the QTc intervals, CYP2D6 enzyme hydroxylation capacity might be relevant in determining the risk for QTc interval lengthening. Patients with impaired CYP2D6 enzyme activity due to enzyme inhibition by thioridazine might be more prone to increased risk of sudden death due to torsade de pointes type cardiac dysrhythmia.

QTc Interval, CYP2D6 and CYP2C9 Genotypes and Risperidone Plasma Concentrations

The role of certain drug metabolizing enzymes in cardiotoxicity, such as CYP2D6 for thioridazine, has been suggested. Risperidone has been shown to inhibit the delayed rectifier leading to lengthening of cardiac repolarization. The heart-rate corrected QT (QTc) interval lengthening has been reported in psychiatric patients receiving risperidone under steady-state conditions. CYP2D6 is involved in the metabolism of risperidone to 9-hydroxy (OH)-risperidone. CYP2C9 enzyme is also involved in the metabolism of several psychotropic drugs, although there are no data about its implication in risperidone metabolism. The present study aimed to evaluate the influence of CYP2D6 and CYP2C9 genotypes, and plasma concentrations of risperidone and 9-OH-risperidone on the QTc interval in patients under steady-state conditions. The relevance of CYP2D6 and CYP2C9 genotypes on risperidone metabolism was also analysed. Thirty-five White European psychiatric patients receiving risperidone monotherapy were studied. QTc interval was longer (p < 0.05) in subjects with one active CYP2D6 gene compared to those with two. The number of CYP2D6 active genes was related to the dose-corrected plasma concentration of risperidone (p < 0.05), the active moiety (risperidone plus 9-OH-risperidone) (p < 0.05) and the risperidone/9-OH-risperidone ratio (p < 0.05). CYP2C9genotypes were not related to plasma concentrations of risperidone or 9-OH-risperidone, nor QTc interval. The results suggest that CYP2D6, but not CYP2C9, may be related to QTc lengthening during treatment with risperidone. The effect of the CYP2D6 genotype in risperidone metabolism is also shown.

Schizophrenia and tobacco smoking in a Spanish psychiatric hospital

This study in a Spanish hospital replicated two US studies suggesting that schizophrenia is associated with smoking when compared with other severe mental illnesses. Neither antipsychotics nor institutionalism could explain this relationship. Seventy of the 100 schizophrenic and 53 of the 100 non-schizophrenic inpatients were current smokers. After correcting for confounding factors, schizophrenia increased the risk of smoking by 2- to 3-fold. Heavy smoking was not associated with schizophrenia.

Association between T102C and A-1438G polymorphisms in the serotonin receptor 2A (5-HT2A) gene and schizophrenia: relevance for treatment with antipsychotic drugs.

Abstract Background: An involvement of serotonin receptor 2A (5-HT2A) in the aetiology of schizophrenia has been hypothesised. The 5-HT2A receptor also appears to be an important site of action of atypical antipsychotic drugs. Indeed, association between schizophrenia and the T102C silent polymorphism of the 5-HTR2A gene has been reported. Another polymorphism in the promoter region of 5-HTR2A (A–1438G) in linkage disequilibrium with the T102C polymorphism has also been reported. It has been suggested that the A–1438G polymorphism alters promoter activity and expression of 5-HT2A receptors and might be responsible for the associations with schizophrenia and the efficacy of atypical antipsychotics such as risperidone. Methods: We analysed the 5-HTR2A T102C and A–1438G polymorphisms in clinically stable schizophrenia patients (SPs) and healthy volunteers (HVs). We developed an allele-specific PCR-based restriction fragment length polymorphism (PCR-RFLP) method. In SPs, we also described differences across both diagnosis subtypes (paranoid vs. non-paranoid) and antipsychotic drug treatment (risperidone vs. other classical antipsychotic drugs). Results: Two groups of 114 SPs and 142 HVs were studied. The frequency of the 5-HTR2A –1438A allele was higher in SPs than in HVs (0.54 vs. 0.44; p<0.05). The frequency of the 102T allele was also higher among SPs than HVs (0.56 vs. 0.46; p<0.05). These two polymorphisms were in linkage disequilibrium. The percentage of carriers of the 1438A/A and 102T/T alleles was 26% and 15% for SPs and HVs, respectively (p<0.05; odds ratio 1.9). No differences in genotype or allele frequencies were found between paranoid and non-paranoid SPs or between SPs on risperidone and those on classical antipsychotic treatment. Conclusions: The present study demonstrates a higher frequency of 5-HTR2A –1438A and 102T alleles in SPs compared to HVs. Clin Chem Lab Med 2007;45:835–8.

Determination of clozapine and its N-desmethyl metabolite by high-performance liquid chromatography with ultraviolet detection

A rapid high-performance liquid chromatographic method has been developed for the simultaneous determination of the atypical antipsychotic drug clozapine and its principal metabolite, N-desmethyl clozapine in human plasma. After liquid-liquid extraction the compounds were separated in a reversed-phase column and measured by ultraviolet absorption at 230 nm. For both compounds inter-day variations were <3.8%, and, based on a plasma sample volume of 2 ml, the limits of quantification were 25 ng/ml. Analytical interference from coadministered psychoactive drugs and their metabolites was also studied, and no interference was found from the most commonly used antidepressants and antipsychotic drugs. The assay is sufficiently sensitive and easy to use for the analysis of plasma samples in human clinical trials and therapeutic drug monitoring.

Increased use of second generation antipsychotic drugs in primary care: potential relevance for hospitalizations in schizophrenia patients

AimTo analyze the changes in the prescribing pattern of antipsychotic drugs in primary care in Extremadura (Spain) from 1990 to 2005, and the potential association with schizophrenia hospitalization rate.MethodsData from 1990–2005 about the prescribing of antipsychotic drugs was drawn from all community pharmacy sales figures reimbursed by the Health System of Extremadura. Drug consumption figures were expressed as the number of defined daily doses per 1,000 inhabitants and per day of treatment (DDD/1,000/day). The total number of annual hospital discharges with the diagnosis of schizophrenia according to DSM-IV criteria from all hospitals in Extremadura from 1 January 1995 to 31 December 2000 was also determined.ResultsThe use of second-generation antipsychotic drugs (SGAs) increased from 0% in 1990–1993 to 78% in 2005. Olanzapine was the most used SGA from 1999–2005. During 1995–2000 the sales of SGAs increased to 50% from 10%. In the same period, the hospitalization rate in schizophrenia patients fell by an average of 12%, which was significantly associated with SGA use (R = −0.88; P = 0.02).DiscussionThe increase in SGAs paralleled the decreased rate of hospitalization in schizophrenia patients. However, the influence of other factors such as SGA use for disorders other than schizophrenia can not be ruled out. Moreover changes in the health-care system, such as the increase in primary mental health care and social rehabilitation programs, may also have a relevant influence.

Relevance of CYP2D6-1584C>G polymorphism for thioridazine:mesoridazine plasma concentration ratio in psychiatric patients

AIMS The CYP2D6 -1584C>G (rs1080985) polymorphism has been identified as another major factor for CYP2D6 function that is possibly associated with ultrarapid metabolism. The mutant -1584G promoter genotype seems to be consistently related to a higher protein expression than -1584C. However, the impact this SNP in the CYP2D6 promoter region has on plasma levels of patients taking CYP2D6 substrates, such as thioridazine, has not been studied. Previously, we showed the validity of the mesoridazine:thioridazine ratio to assess CYP2D6 activity in clinical settings. Therefore, the aim of this study was to analyze the relationship between the presence of the CYP2D6 -1584C>G polymorphism and the plasma concentrations of thioridazine and its metabolites in a previously studied population of patients in order to evaluate the implications for CYP2D6 hydroxylation capacity. MATERIALS & METHODS The CYP2D6 -1584C>G polymorphism was determined by using a PCR-RFLP method in 61 Caucasian psychiatric patients receiving thioridazine monotherapy. RESULTS Among patients with two active CYP2D6 genes, there were significant differences in the thioridazine:mesoridazine plasma concentrations ratio (p < 0.05) among the three CYP2D6 -1584C>G genotype groups. Moreover, in this group of patients the thioridazine:mesoridazine ratio was lower (p < 0.05) in carriers of CYP2D6 -1584G allele than in patients homozygous for CYP2D6 -1584C allele. However, no differences in thioridazine or its metabolite concentrations between homozygous CYP2D6 -1584C allele carriers and carriers of the -1584G allele were found. CONCLUSION According to the present results the concentration ratio of thioridazine to mesoridazine was related to the CYP2D6 -1584C>G polymorphism. It is likely that individuals who carry CYP2D6 -1584G versus homozygotes for the -1584C allele may present an increased CYP2D6 activity.

QTc interval lengthening and debrisoquine metabolic ratio in psychiatric patients treated with oral haloperidol monotherapy

The increased prevalence of the potentially life-threatening torsade de pointes type of arrhythmias and sudden cardiac death in psychiatric patients receiving antipsychotic drugs has become a public concern [1, 2]. The prolonged heart-rate-corrected QT interval (QTc) in the electrocardiogram (ECG) is a warning sign of this potentially fatal side effect [2]. Prolonged QTc interval may be a genetically inherited trait or the effect of drug treatment [1]. Several antipsychotic drugs has been associated with QTc lengthening and sudden cardiac death, such as thioridazine, droperidol, pimozide, or sulpiride [3]. Haloperidol is a butyrophenon-type antipsychotic drug which is widely used in the treatment of different psychiatric disorders and also in surgery and anesthesia. Haloperidol seems also to have an effect on the QTc interval and may increase the risk of torsade de pointes arrhythmia after intravenous [4] and oral doses [5]. Around 7% of Caucasian individuals have decreased capacity to metabolize debrisoquine by the polymorphic drug-metabolizing enzyme cytochrome P450 (CYP)2D6 [6]. The relationship between CYP2D6 activity and haloperidol plasma concentration has been shown in healthy volunteers [7] and also in patients [8]. Thus, enzyme activity may be associated with a tendency to cardiac arrhythmias in patients during treatment. The present study aimed to determine the effect of CYP2D6 enzyme activity, haloperidol dose, and plasma concentrations on the QTc interval among patients receiving oral haloperidol monotherapy. Twenty-seven Spanish, Caucasian psychiatric patients without any relevant organic disease were studied. The patients were receiving oral haloperidol (Haloperidol, Syntex Latino, Barcelona, Spain) monotherapy for at least 14 days. The dose range was 1.5–30 mg/day, and the average dose was 7±5 mg/day (mean±SD). The mean age of the patients was 47±15 years (range: 23– 77 years), and 22 (81%) were males. All patients were phenotyped using debrisoquine during antipsychotic drug treatment. After an overnight fast the subjects took a single oral dose of 10 mg debrisoquine sulfate (Declinax, Hoffman-La Roche, Switzerland), and all urine was collected over 8 h. Urine concentrations of debrisoquine and 4-hydroxy-debrisoquine were measured using gas chromatography [9]. Debrisoquine metabolic ratio (MR) was calculated as the ratio of the molar concentration of the parent drug to that of 4-hydroxy-debrisoquine in the 0-h to 8-h urine. Plasma concentrations of haloperidol were measured using high-performance liquid chromatography according to a previously published method [7, 8]. Cardiologic examination was performed with a routine, clinically used ECG apparatus, which calculated automatically the QTc intervals. The mean QTc interval of the patients was 418.1±48.0 ms. Three patients of 27 (11.1%) could be identified to have a QTc interval longer than 456 ms (481, 549, and 565 ms), which may be considered as the cut-off value for limit of risk of cardiac arrhythmia [10, 11] (Fig. 1). Reilly et al. [10] reported that 13.9% of patients receiving haloperidol treatment had lengthened QTc intervals and found an almost significantly increased odds ratio for QTc lengthening by haloperidol. The proportion of patients with QTc interval over 456 ms in the present study was similar to that (11.1%) thus supporting the effect of haloperidol treatment on QTc interval at clinically used oral doses. There was a great interindividual variability in haloperidol plasma levels. The steady-state dose-corrected plasma concentrations of haloperidol showed approximately eightfold interindividual variation (from 0.12 lg/l/mg to 0.92 lg/l/mg). The dose and plasma Eur J Clin Pharmacol (2002) 58: 223–224 DOI 10.1007/s00228-002-0452-7

High-performance liquid chromatography method using ultraviolet detection for the quantification of aripiprazole and dehydroaripiprazole in psychiatric patients.

Abstract Background: Aripiprazole (ARI) is an antipsychotic drug that is metabolized to dehydroaripiprazole (DARI) by CYP2D6. Because of the large interindividual variability in ARI and DARI plasma concentrations, therapeutic drug monitoring may be of use in psychiatric patients during treatment with ARI. The aim of the present study was to develop a simple and reliable method for the quantitative determination of ARI and DARI in plasma using liquid-liquid extraction and reverse-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection. The method was tested in psychiatric patients during regular treatment with ARI. Methods: Separation was by the liquid-liquid method, and UV detection at 254 nm. Linear responses for ARI and DARI were obtained between 2 and 1000 ng/mL, and precision assays were lower than 10.4 for both analytes. Results: Lower limit of quantification and detection were 1 and 0.38 ng/mL for ARI and 0.78 and 0.44 ng/mL for DARI, respectively. The method was successfully applied to plasma samples drawn from 22 patients with concentrations ranging between 2 and 189 ng/mL for ARI and between 11 and 359 ng/mL for DARI. Conclusions: The chromatographic method developed has been demonstrated to be sensitive and reliable for the measurement of ARI and DARI simultaneously in human plasma, and the present method represents an alternative procedure to evaluate plasma concentration in patients during treatment with ARI.

No effect of the CYP1A2*1F genotype on thioridazine, mesoridazine, sulforidazine plasma concentrations in psychiatric patients

Sir, Recently it has been shown that CYP1A2 and CYP3A4 are the main enzymes responsible for 5-sulfoxidation and Ndemethylation of thioridazine, whereas CYP2D6 is the basic enzyme that catalyzes mono-2and di-2-sulfoxidation in human liver microsomomes. Moreover, both CYP2D6 and CYP3A4 contribute to thioridazine mono-2-sulfoxidation [1]. Previously, on the basis of CYP2D6 involvement in the metabolism of thioridazine to mesoridazine we showed the use of the mesoridazine-to-thioridazine ratio as a tool to assess CYP2D6 activity in clinical settings [2]. Additionally, we reported that CYP2D6 genotype mediated the dosedependent inhibition of CYP2D6 during treatment with thioridazine [3]. Later our group reported in this journal [4] that thioridazine plasma concentration in psychiatric patients was influenced by CYP2D6 genotypes and tobacco smoking, which suggested that both CYP1A2 and CYP2D6 enzymes were involved in the metabolism of thioridazine. The observation that thioridazine plasma concentration corrected by dose was lower in smokers than non-smokers [4] could be due to CYP1A2 inducibility by smoking [5]. This fact is of note considering the high proportion of tobacco smokers among schizophrenic patients [6]. A possible impact of CYP1A2 on thioridazine metabolism is also supported by previous data showing that thioridazine plasma concentration increases during treatment with the CYP1A2 potent inhibitor fluvoxamine [7]. A putative polymorphism in intron 1 of CYP1A2 (-163C> A; CYP1A2*1F allele) appears to affect the inducibility of CYP1A2 [8]. Thus, the CYP1A2*1F A/A genotype may represent a CYP1A2 with high inducibility, which may either be a direct cause of increased CYP1A2 activity, or be genetically linked to polymorphisms conferring high inducibility [9]. The aim of this study was to analyse the potential influence of high-inducibility CYP1A2*1F allele and tobacco smoking on thioridazine and metabolite plasma concentration. Fifty-nine Caucasian psychiatric patients receiving thioridazine monotherapy were studied (44 smokers and 15 non-smokers) for the determination of CYP1A2*1F genotypes. These patients are part of a previously studied population of 76 patients [4]. CYP2D6 genotypes, debrisoquine metabolic ratio and steady-state plasma levels of Eur J Clin Pharmacol (2007) 63:527–528 DOI 10.1007/s00228-007-0284-6