Clinical Significance of a CYP2D6 Poor Metabolizer -A Patient With Schizophrenia on Risperidone Treatment

Physiologically Based Pharmacokinetic Modelling to Describe the Pharmacokinetics of Risperidone and 9-Hydroxyrisperidone According to Cytochrome P450 2D6 Phenotypes

BACKGROUND AND OBJECTIVES

The genetic polymorphism of cytochrome P450 (CYP) 2D6 is characterized by an excessive impact on positive and adverse drug reactions to antipsychotics, such as risperidone. Consequently, the pharmacokinetics of the drug and metabolite can be substantially altered and exhibit a high variability between the different phenotypes. The goal of this study was to develop a physiologically based pharmacokinetic (PBPK) model considering the CYP2D6 genetic polymorphism for risperidone and 9-hydroxyrisperidone (9-OH-RIS) taking CYP3A4 into account. Additionally, risperidone dose adjustments, which would compensate for genetically caused differences in the plasma concentrations of the active moiety (sum of risperidone and 9-OH-RIS) were calculated.

METHODS

Based on available knowledge about risperidone, 9-OH-RIS, and relevant physiological changes according to different CYP2D6 phenotypes, several PBPK models were built. In addition, an initial model was further evaluated based on the plasma concentrations of risperidone and 9-OH-RIS from a single-dose study including 71 genotyped healthy volunteers treated with 1 mg of oral risperidone.

RESULTS

PBPK models were able to accurately describe risperidone exposure after single-dose administration, especially in the concentration range ≥ 1 µg/L, illustrated by a minimal bias and a good precision. About 90.3% of all weighted residuals versus observed plasma concentrations ≥ 1 µg/L were in the ± 30% range. The risperidone/9-OH-RIS ratio increased progressively according to reduced CYP2D6 activity, resulting in a mean ratio of 4.96 for poor metabolizers. Simulations demonstrate that dose adjustment of the drug by - 25% for poor metabolizers and by - 10% for intermediate metabolizers results in a similar exposure to that of extensive metabolizers. Conversely, the risperidone/9-OH-RIS ratio can be used to determine the phenotype of individuals.

CONCLUSION

PBPK modelling can provide a valuable tool to predict the pharmacokinetics of risperidone and 9-OH-RIS in healthy volunteers, according to the different CYP2D6 phenotypes taking CYP3A4 into account. These models are able to ultimately support decision-making regarding dose-optimization strategies, especially for subjects showing lower CYP2D6 activity.

Effect of CYP2D6 polymorphisms on plasma concentration and therapeutic effect of risperidone

BACKGROUND

This study aimed to investigate the influence of CYP2D6 polymorphisms on risperidone plasma concentrations in patients with schizophrenia. Based on pharmacogenomics, we examined whether plasma concentration of risperidone is associated with clinical response and adverse side-effects.

METHODS

We recruited patients with chronic schizophrenia who were then treated with risperidone. The CYP2D6 genotypes were determined using targeted sequencing. All high-frequency mutation sites of the nine exons of the gene were assayed in the present study. Plasma concentrations of risperidone and 9-hydroxyrisperidone (9-OH-RIS) were measured using high-performance liquid chromatography (HPLC). Psychiatric symptoms were monitored using The Positive and Negative Syndrome Scale (PANSS), Brief Psychiatric Rating Scale (BPRS), and Clinical Global Impression (CGI). Adverse effects were evaluated using the Barnes Akathisia Scale (BAS) and Extrapyramidal Symptom Rating Scale (ESRS). Follow-up visits were scheduled at weeks 2,4, and 8 after treatment initiation.

RESULTS

Among the 76 patients, 100 C > T (rs1065852), 1038 C > T (rs1081003), 1662 G > C (rs1058164), 2851 C > T (rs16947), and 4181G > C (rs1135840) variants were detected. The most common allele was CYP2D6*10 (81.6%), whereas CYP2D6*2 (9.2%) and CYP2D6*5 (17.1%) were relatively rare. Plasma levels of risperidone and the risperidone/9-OH risperidone ratio (R/9-OH) were significantly increased in individuals with CYP2D6*10 (P < 0.05). The change in PANSS score, weight, high-density lipoprotein (HDL) level, prolactin (PRL) level, and ESRS were significantly different from baseline, between the different genotypes (P < 0.01). Moreover, individuals with CYP2D6*10 homozygous (TT) mutations were associated with higher risperidone concentration and R/9-OH ratio than those with heterozygous mutations (CT) (P < 0.01). A change from baseline in BPRS scores was observed only during week 8 and was different between heterozygous and homozygous mutations. As for the C2851T polymorphism, the incidence of adverse metabolic effects was significantly different between the C/C and C/T genotypes (P < 0.01). Regarding the G4181C polymorphisms, the changes from baseline in GLU and TG, were different between the C/C and C/G genotypes (P < 0.01).

CONCLUSIONS

The genotype of CYP2D6 significantly influences the plasma concentration of risperidone and may subsequently influence the adverse side-effects following risperidone treatment, while also exerting a slight influence on clinical outcomes.

CYP2D6 polymorphisms and their influence on risperidone treatment

Cytochrome P450 enzyme especially CYP2D6 plays a major role in biotransformation. The interindividual variations of treatment response and toxicity are influenced by the polymorphisms of this enzyme. This review emphasizes the effect of CYP2D6 polymorphisms in risperidone treatment in terms of basic knowledge, pharmacogenetics, effectiveness, adverse events, and clinical practice. Although the previous studies showed different results, the effective responses in risperidone treatment depend on the CYP2D6 polymorphisms. Several studies suggested that CYP2D6 polymorphisms were associated with plasma concentration of risperidone, 9-hydroxyrisperidone, and active moiety but did not impact on clinical outcomes. In addition, CYP2D6 poor metabolizer showed more serious adverse events such as weight gain and prolactin than other predicted phenotype groups. The knowledge of pharmacogenomics of CYP2D6 in risperidone treatment is increasing, and it can be used for the development of personalized medication in term of genetic-based dose recommendation. Moreover, the effects of many factors in risperidone treatment are still being investigated. Both the CYP2D6 genotyping and therapeutic drug monitoring are the important steps to complement the genetic-based risperidone treatment.

Factors affecting the development of adverse drug reactions to β-blockers in hospitalized cardiac patient population

The aim of the present study was to undertake a study on the prevalence of cytochrome P450 2D6 (CYP2D6) poor metabolizer alleles (*3, *4, *5, and *6) on a Montenegrin population and its impact on developing adverse drug reactions (ADRs) of β-blockers in a hospitalized cardiac patient population. A prospective study was conducted in the Cardiology Center of the Clinical Center of Montenegro and included 138 patients who had received any β-blocker in their therapy. ADRs were collected using a specially designed questionnaire, based on the symptom list and any signs that could point to eventual ADRs. Data from patients' medical charts, laboratory tests, and other available parameters were observed and combined with the data from the questionnaire. ADRs to β-blockers were observed in 15 (10.9%) patients. There was a statistically significant difference in the frequency of ADRs in relation to genetically determined enzymatic activity (P<0.001), with ADRs' occurrence significantly correlating with slower CYP2D6 metabolism. Our study showed that the adverse reactions to β-blockers could be predicted by the length of hospitalization, CYP2D6 poor metabolizer phenotype, and the concomitant use of other CYP2D6-metabolizing drugs. Therefore, in hospitalized patients with polypharmacy CYP2D6 genotyping might be useful in detecting those at risk of ADRs.

Risperidone-associated adverse drug reactions and CYP2D6 polymorphisms in a South African cohort

Background

Contradictory information exists regarding the influence of CYP2D6 polymorphisms on adverse drug reactions (ADRs) (extrapyramidal symptoms (EPS) and weight gain) related to risperidone treatment. This prompted us to evaluate the influence of CYP2D6 genetic variation in a cohort of South African patients who presented with marked movement disorders and/or weight gain while on risperidone treatment.

Methods

Patients who were experiencing marked risperidone ADRs were recruited from Weskoppies Public Psychiatric Hospital. As poor or intermediate metabolism was expected, comprehensive CYP2D6 sequence variations were evaluated using XL-PCR + Sequencing.

Results

No statistically significant association was found between CYP2D6 poor metabolism and risperidone ADRs. An inverse relationship between EPS and weight gain was however identified. A novel CYP2D6 allele was identified which is unlikely to affect metabolism based on in silico evaluation.

Conclusion

CYP2D6 variation appeared not to be a good pharmacogenetic marker for predicting risperidone-related ADRs in this naturalistic South African cohort. Evaluation of a larger cohort would be needed to confirm these observations, including an examination of the role of potential intermediaries between the hypothesised genetic and clinical phenotypes.

Relationship between P-glycoprotein and second-generation antipsychotics

The membrane transport protein P-glycoprotein (P-gp) is an interesting candidate for individual differences in response to antipsychotics. To present an overview of the current knowledge of P-gp and its interaction with second-generation antipsychotics (SGAs), an internet search for all relevant English original research articles concerning P-gp and SGAs was conducted. Several SGAs are substrates for P-gp in therapeutic concentrations. These include amisulpride, aripiprazole, olanzapine, perospirone, risperidone and paliperidone. Clozapine and quetiapine are not likely to be substrates of P-gp. However, most antipsychotics act as inhibitors of P-gp, and can therefore influence plasma and brain concentrations of other substrates. No information was available for sertindole, ziprasidone or zotepine. Research in animal models demonstrated significant differences in antipsychotic brain concentration and behavior owing to both P-gp knockout and inhibition. Results in patients are less clear, as several external factors have to be accounted for. Patients with polymorphisms which decrease P-gp functionality tend to perform better in clinical settings. There is some variability in the findings concerning adverse effects, and no definitive conclusions can be drawn at this point.

The role of CYP2D6 and ABCB1 pharmacogenetics in drug-naïve patients with first-episode schizophrenia treated with risperidone

PURPOSE

To evaluate the role of cytochrome 450 2D6 (CYP2D6) and ABCB1 variants on plasma risperidone concentrations and treatment response in 83 drug-naive patients experiencing a first episode of psychosis.

METHODS

All patients were treated with risperidone for 8 weeks. The CYP2D6 genotyping was performed by allele-specific PCR-restriction fragment length polymorphism analysis (for alleles *3,*4,*6) and long-distance PCR (for duplications and allele *5), while real-time PCR analysis was used for the ABCB1 G2677T/A and C3435T variants. Plasma concentrations of risperidone and 9-OH risperidone were measured by high-performance liquid chromatography.

RESULTS

The number of patients with the CYP2D6 wild type (wt)/wt, wt/mutation (mut) and mut/mut genotype was 43, 32 and 8, respectively. The number of patients with the ABCB1 2677G/G, G/T and T/T variants was 29, 42 and 12, respectively; those with the 3435CC, C/T and T/T variants was 25, 37 and 21, respectively. The CYP2D6 genotype had a strong effect on the steady-state dose-corrected plasma levels (C/D) of risperidone, its 9-OH metabolite and the active moiety, while the ABCB1 2677 T/T and 3435 T/T genotypes has similarly strong effects on the active moiety C/D. The CYP2D6 poor metabolizers had a significantly higher risperidone C/D and active moiety C/D and lower 9-OH risperidone C/D. The ABCB1 3435 T allele and the ABCB1 2667 T-3435 T haplotype carriers were more frequent among subjects without extrapyramidal syndromes. Patients showed significant improvements in positive and general symptoms, but not in negative symptoms. These changes were not related to variations in genetic and drug concentration data.

CONCLUSION

Our findings suggest that CYP2D6 and ABCB1 G2677T and C3435T may be useful determinants of risperidone plasma concentrations, but the clinical implications of these associations in relation to treatment response and side-effects remain unclear.