Effect of CYP2D6, CYP3A5, and MDR1 genetic polymorphisms on the pharmacokinetics of risperidone and its active moiety

Impact of the ABCB1 gene polymorphism on plasma 9-hydroxyrisperidone and active moiety levels in Japanese patients with schizophrenia

9-Hydroxyrisperidone (9-OH-RIS) is an active metabolite of the antipsychotic drug risperidone (RIS). The total active moiety level, in other words the sum of the RIS and 9-OH-RIS serum levels, may be important for estimating the clinical effects of RIS treatment. However, there have been no consistent results reported regarding the relationship between cytochrome P450 (CYP) 2D6 or adenosine triphosphate-binding cassette subfamily B member 1 (ABCB1) variant alleles and 9-OH-RIS or total active moiety plasma levels. Seventy-four Japanese patients treated with RIS were examined in the present study. Steady-state plasma RIS and 9-OH-RIS were measured. The CYP2D6*5, CYP2D6*10, ABCB1 3435C>T, and ABCB1 2677G>T/A genotypes were detected. Multiple regression analysis showed that the dose-corrected plasma RIS levels were significantly correlated with the number of CYP2D6 variant alleles and ABCB1 3435C>T genotypes, whereas the 9-OH-RIS and total active moiety levels were significantly correlated with the ABCB1 3435C>T genotypes and with age. On the other hand, the ABCB1 2677G>T/A genotypes did not affect plasma RIS, 9-OH-RIS, or total active moiety levels. The ABCB1 3435C>T genetic polymorphism may predict plasma 9-OH-RIS and total active moiety levels.

Population pharmacokinetic modeling of risperidone and 9-hydroxyrisperidone to estimate CYP2D6 subpopulations in children and adolescents

AIM

The study aims were to characterize risperidone and (±)-9-hydroxyrisperidone pharmacokinetic (PK) variability in children and adolescents and to evaluate covariate effects on PK parameters.

METHODS

Steady-state samples were drawn at predose, 1, 2, 4, and 7 hours postdose; cytochrome P450 2D6 (CYP2D6) genotypes were available for 28 subjects. A nonlinear mixed-effects model (NONMEM) modeled the PKs of risperidone and (±)-9-hydroxyrisperidone; covariates included age, weight, sex, and CYP2D6 phenotype. The model included 497 observations [risperidone (n = 163), (+) and (-)-9-hydroxyrisperidone (n = 334)] from 45 subjects aged 3-18.3 (mean 9.6 ± 3.7) years, weighing 16.8-110 (43 ± 20.2) kg.

RESULTS

A 1-compartment mixture model described risperidone and (±)-9-hydroxyrisperidone clearances for 3 CYP2D6 metabolizer subpopulations: extensive, intermediate, and poor. Weight significantly affected (±)-9-hydroxyrisperidone clearance. Clearance estimates in the mixture model were poor metabolizer 9.38 L/h, intermediate metabolizer 29.2 L/h, and extensive metabolizer 37.4 L/h.

CONCLUSION

Active moiety [risperidone plus (±)-9-hydroxyrisperidone] PK variability and the covariate effects were better explained with the addition of metabolite PK parameters. This model may aid the development of individualized risperidone dosing regimens in children and adolescents.

Polymorphisms influencing olanzapine metabolism and adverse effects in healthy subjects

OBJECTIVE

The pharmacokinetics of olanzapine and response to treatment could be affected by polymorphisms in genes coding for drug-metabolizing enzymes, transporters, or receptors. The aim of this study was to identify genetic markers predictive of pharmacokinetics, pharmacodynamics, and adverse effects of olanzapine.

METHODS

Sixty-three healthy volunteers receiving a single 5-mg oral dose of olanzapine were genotyped for 39 genetic variants that could be related to the response to olanzapine. All genetic variants were analyzed by PharmaChip, but DRD2 Taq1A polymorphism was determined by real-time polymerase chain reaction. Olanzapine was measured using high-performance liquid chromatography combined with tandem mass spectrometry. The relationship of gender and polymorphisms with olanzapine pharmacokinetics, the change in prolactin levels, and the incidence of adverse effects were evaluated by multiple regression analysis.

RESULTS

The pharmacokinetics of olanzapine was influenced by polymorphisms in CYP3A5, GSTM3, and GRIN2B. Prolactin levels were affected by gender and polymorphisms in DRD2 and 5-HTR2A. Polymorphisms in CYP2C9, TPMT, UGT1A1, MDR1, and 5-HTR2A were related to some adverse effects of olanzapine.

CONCLUSIONS

Several polymorphisms can explain differences in the pharmacokinetics, pharmacodynamics, and safety of olanzapine in healthy subjects. Whether these genetic factors influence the risk of therapeutic failure or tolerability in patients remains to be established.

Pharmacogenomics can improve antipsychotic treatment in schizophrenia

Schizophrenia is a widespread mental disease with a prevalence of about 1% in the world population, and heritability of up to 80%. Drug therapy is an important approach to treating the disease. However, the curative effect of antipsychotic is far from satisfactory in terms of tolerability and side effects. Many studies have indicated that about 30% of the patients exhibit little or no improvements associated with antipsychotics. The response of individual patients who are given the same dose of the same drug varies considerably. In addition, antipsychotic drugs are often accompanied by adverse drug reactions (ADRs), which can cause considerable financial loss in addition to the obvious societal harm. So, it is strongly recommended that personalized medicine should be implemented both to improve drug efficacy and to minimize adverse events and toxicity. There is therefore a need for pharmacogenomic studies into the factors affecting response of schizophrenia patients to antipsychotic drugs to provide informed guidance for clinicians. Individual differences in drug response is due to a combination of many complex factors including ADEM (absorption, distribution, metabolism, excretion) process, transporting, binding with receptor and intracellular signal transduction. Pharmacogenetic and pharmacogenomic studies have successfully identified genetic variants that contribute to this interindividual variability in antipsychotics response. In addition, epigenetic factors such as methylation of DNA and regulation by miRNA have also been reported to play an important role in the complex interactions between the multiple genes and environmental factors which influence individual drug response phenotypes in patients. In this review, we will focus on the latest research on polymorphisms of candidate genes that code for drug metabolic enzymes (CYP2D6, CYP1A2, CYP3A4, etc.), drug transporters (mainly ABCB1) and neurotransmitter receptors (dopamine receptors and serotonin receptors, etc.). We also discuss the genome-wide pharmacogenomic study of schizophrenia and review the current state of knowledge on epigenetics and potential clinical applications.

Psychotropic drug-drug interactions involving P-glycoprotein

Multidrug resistance P-glycoprotein (P-gp; also known as MDR1 and ABCB1) is expressed in the luminal membrane of the small intestine and blood-brain barrier, and the apical membranes of excretory cells such as hepatocytes and kidney proximal tubule epithelia. P-gp regulates the absorption and elimination of a wide range of compounds, such as digoxin, paclitaxel, HIV protease inhibitors and psychotropic drugs. Its substrate specificity is as broad as that of cytochrome P450 (CYP) 3A4, which encompasses up to 50 % of the currently marketed drugs. There has been considerable interest in variations in the ABCB1 gene as predictors of the pharmacokinetics and/or treatment outcomes of several drug classes, including antidepressants and antipsychotics. Moreover, P-gp-mediated transport activity is saturable, and is subject to modulation by inhibition and induction, which can affect the pharmacokinetics, efficacy or safety of P-gp substrates. In addition, many of the P-gp substrates overlap with CYP3A4 substrates, and several psychotropic drugs that are P-gp substrates are also CYP3A4 substrates. Therefore, psychotropic drugs that are P-gp substrates may cause a drug interaction when P-gp inhibitors and inducers are coadministered, or when psychotropic drugs or other medicines that are P-gp substrates are added to a prescription. Hence, it is clinically important to accumulate data about drug interactions through studies on P-gp, in addition to CYP3A4, to assist in the selection of appropriate psychotropic medications and in avoiding inappropriate combinations of therapeutic agents. There is currently insufficient information available on the psychotropic drug interactions related to P-gp, and therefore we summarize the recent clinical data in this review.

Pharmacogenetic analysis of pediatric patients with acute lymphoblastic leukemia: a possible association between survival rate and ITPA polymorphism

Genetic polymorphisms are important factors in the effects and toxicity of chemotherapeutics. To analyze the pharmacogenetic and ethnic differences in chemotherapeutics, major genes implicated in the treatment of acute lymphoblastic leukemia (ALL) were analyzed. Eighteen loci of 16 genes in 100 patients with ALL were analyzed. The distribution of variant alleles were CYP3A4*1B (0%), CYP3A5*3 (0%), GSTM1 (21%), GSTP1 (21%), GSTT1 (16%), MDR1 exon 21 (77%), MDR1 exon 26 (61%), MTHFR 677 (63%), MTHFR 1298 (29%), NR3C1 1088 (0%), RFC1 80 (68%), TPMT combined genotype (7%), VDR intron 8 (11%), VDR FokI (83%), TYMS enhancer repeat (22%) and ITPA 94 (30%). The frequencies of single nucleotide polymorphisms (SNPs) of 10 loci were statistically different from those in Western Caucasians. Dose percents (actual/planned dose) or toxicity of mercaptopurine and methotrexate were not related to any SNPs. Event free survival (EFS) rate was lower in ITPA variants, and ITPA 94 AC/AA variant genotypes were the only independent risk factor for lower EFS in multivariate analysis, which was a different pharmacogenetic implication from Western studies. This study is the first pharmacogenetic study in Korean pediatric ALL. Our result suggests that there are other possible pharmacogenetic factors besides TPMT or ITPA polymorphisms which influence the metabolism of mercaptopurine in Asian populations.

CYP3A5 polymorphism in Mexican renal transplant recipients and its association with tacrolimus dosing

BACKGROUND AND AIMS

Variability in CYP3A5 expression associated with differences in tacrolimus bioavailability has been documented. The wild-type allele CYP3A5*1 expresses the functional protein, whereas the CYP3A5*3 allele is a splice variant with a premature stop codon and encodes a truncated nonfunctional protein. The aim of the study was to determine the frequency of CYP3A5*1 and CYP3A5*3 in 291 (124 adults, 167 pediatric) Mexican renal transplant recipients, evaluate the tacrolimus dose requirements by genotype and compare genotype frequency data with that of other populations.

METHODS

We carried out a multicenter study. Patients were recruited from three institutions located in Mexico City. Genotyping of the CYP3A5*1 and CYP3A5*3 alleles was performed by direct DNA sequencing.

RESULTS

Eighteen patients (6.2%) were CYP3A5*1*1 homozygous carriers or functional protein expresser homozygous, 121 patients (41.6 %) were CYP3A5*1*3 were heterozygous carriers or heterozygous expressers, and 152 patients (52.2%) were CYP3A5*3*3 homozygous carriers or homozygous nonexpressers. There was a statistically significant difference in frequency of the functional and nonfunctional expresser phenotypes from those reported for Black and Caucasian, but not for South Asian populations. The CYP3A5 phenotype had a significant impact in tacrolimus bioavailability, as wild-type carriers required higher dosing compared to mutated carriers to achieve similar drug trough levels. Patients with CYP3A5*1*1 genotype had a median dose requirement of 0.16 mg/kg/day, CYP3A5*1*3 patients had a median tacrolimus dose of 0.13 mg/kg/day and CYP3A5*3*3 had a median dose of 0.07 mg/kg/day (Kruskal-Wallis, p <0.0001).

CONCLUSIONS

Of the Mexican transplant recipients, 52.2% were CYP3A5*3*3 and required significantly lower tacrolimus dose than those with CYP3A5*1 allele.

Comparative fasting bioavailability of dispersible and conventional tablets of risperidone: a single-dose, randomized-sequence, open-label, two-period crossover study in healthy male Chinese volunteers

BACKGROUND

Risperidone (RIS), an atypical antipsychotic drug, is used for the treatment of psychoses associated with schizophrenia and other psychiatric disorders in adult and pediatric populations. An oral dispersible tablet formulation of risperidone has been developed. This study was conducted to provide support for marketing authorization of this drug in China.

OBJECTIVE

This study was designed to compare the pharmacokinetic (PK) properties and bioavailability of 2 RIS formulations-the dispersible formulation (test) and a branded formulation (reference) in healthy male Chinese volunteers.

METHODS

This single-dose, randomized-sequence, open-label, 2-period crossover study involved 22 healthy male Chinese volunteers. Equal numbers of eligible participants were randomly assigned to receive either the test drug (2 mg) or the same dose of the reference formulation, followed by a 2-week washout period and administration of the alternate formulation. The study drugs were administered after a 10-hour overnight fast. Blood samples were collected before dosing and at 0.33, 0.67, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 15, 24, 36, 48, 72, and 96 hours after dosing. Plasma concentrations of RIS and its active metabolite, 9-hydroxyrisperidone (9-OH-RIS), were measured using LC-MS/MS. The safety profile was evaluated by recording adverse events (AEs), assessed using physical examination including vital signs, spontaneous reporting, and clinical laboratory results. The 2 formulations were considered to have met the requirements for bioequivalence if the 90% CIs for the log-transformed C(max) and AUC values were within the predetermined ranges of 75% to 133% and 80% to 125%, respectively, according to the guidelines of the State Food and Drug Administration (SFDA) of China.

RESULTS

All 22 volunteers (mean [SD] age, 22.2 [1.98] years; weight, 64.07 [5.93] kg; height, 173 [5] cm; and body mass index, 21.2 [1.67] kg/m(2)) that were enrolled completed the study. For RIS, the 90% CIs for the ratios of C(max), AUC(0-t), and AUC(0-∞) were 93.2% to 116.7%, 97.9% to 111.3%, and 98.0% to 111.6%, respectively. For 9-OH-RIS, the 90% CIs were 95.8% to 113.9%, 100.2% to 109.7%, and 100.5% to 110.3%, respectively. All values were within the predetermined bioequivalence range. Seven AEs were reported somnolence (4 subjects [9.1%]) and dizziness (3 subjects [6.8%]). All AEs were transient and considered mild by physicians.

CONCLUSIONS

The test (dispersible) and reference tablets met the regulatory criteria for bioequivalence as defined by the SFDA. Both formulations were well tolerated. Chinese Clinical Trials registration number: ChiCTR-TRC-12001996.

Effect of the cytochrome P450 2D6*10 allele on risperidone metabolism in Japanese psychiatric patients

OBJECTIVE

The sum of the serum levels of risperidone (RIS) and 9-hydroxyrisperidone (9-OH-RIS), which is the active moiety serum level, could be important for estimating the clinical effects of RIS. However, there have been no consistent results reported about the relationship between cytochrome P450 (CYP) 2D6*10 allele and plasma 9-OH-RIS or active moiety levels. We investigated the effect of the number of CYP2D6*10 alleles on steady-state plasma RIS, 9-OH-RIS, and active moiety levels in Japanese patients.

METHODS

Steady-state plasma RIS, 9-OH-RIS, and active moiety levels were measured in 64 patients treated with an average dosage of 4.6 mg/day.

RESULTS

The number of CYP2D6*10 alleles significantly affected dose-corrected plasma RIS levels (p = 0.001), and the median concentrations in ng/ml/mg were 0.94 (0 allele) vs. 1.73 (1 allele) vs. 3.05 (2 alleles). The number of CYP2D6*10 alleles did not affect plasma 9-OH-RIS or active moiety levels.

CONCLUSION

The present study shows that the number of CYP2D6*10 alleles affected plasma RIS levels but not plasma 9-OH-RIS and plasma active moiety levels. Because the plasma active moiety levels can influence antipsychotic effects or side effects, the genetic screening of the CYP2D6*10 allele for RIS in Asian populations may not be clinically important.

Functional significance of genetic polymorphisms in P-glycoprotein (MDR1, ABCB1) and breast cancer resistance protein (BCRP, ABCG2)

Recent pharmacogenomic/pharmacogenetic (PGx) studies have disclosed important roles for drug transporters in the human body. Changes in the functions of drug transporters due to drug/food interactions or genetic polymorphisms, for example, are associated with large changes in pharmacokinetic (PK) profiles of substrate drugs, leading to changes in drug response and side effects. This information is extremely useful not only for drug development but also for individualized treatment. Among drug transporters, the ATP-binding cassette (ABC) transporters are expressed in most tissues in humans, and play protective roles; reducing drug absorption from the gastrointestinal tract, enhancing drug elimination into bile and urine, and impeding the entry of drugs into the central nervous system and placenta. In addition to PK/pharmacodynamic (PD) issues, ABC transporters are reported as etiologic and prognostic factors (or biomarkers) for genetic disorders. Although a consensus has not yet been reached, clinical studies have demonstrated that the PGx of ABC transporters influences the overall outcome of pharmacotherapy and contributes to the pathogenesis and progression of certain disorders. This review explains the impact of PGx in ABC transporters in terms of PK/PD, focusing on P-glycoprotein and breast cancer resistance protein (BCRP).

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.

Atypical Antipsychotics for the Treatment of ICU Delirium

Delirium is commonly described in critically ill patients as 1 factor contributing to increased length of intensive care unit and hospital stay, secondary complications, and increased mortality. Initial screening tools for delirium in hospitalized patients are generally easy to use; however, many centers have struggled with implementing these tools in a consistent and systematic manner. Haloperidol has traditionally been prescribed as the primary agent of choice for the treatment of delirium in critically ill patients. Clinicians have been challenged to consider alternative agents due to adverse effects such as extrapyramidal symptoms, QTc prolongation, and possible torsades de pointes with haloperidol use. The atypical antipsychotics are attractive alternatives to haloperidol with improved safety profiles but are flawed by limited data to support dosing and efficacy in this patient population. Future studies that provide large, prospective, double-blinded, placebo-controlled data to support the implementation of these agents as standard therapy over haloperidol are needed.

Tacrolimus dosing in Chinese renal transplant recipients: a population-based pharmacogenetics study

OBJECTIVES

The aims of this study were to examine the effects of genetic and clinical factors on the maintenance dose of tacrolimus in patients following renal transplantation and to develop a tacrolimus-dosing model that could be combined with associated factors.

PATIENTS AND METHODS

This study included 142 renal transplant recipients who received tacrolimus as immunosuppressive agent. CYP3A5, MDR1 and NR1I2 gene polymorphisms were identified based on the SNaPshot assay. The relationship between the genetic and clinical factors and tacrolimus maintenance dose as well as between dose-corrected tacrolimus concentration was examined.

RESULTS

CYP3A5 genotype, body weight, haematocrit, haemoglobin and total bilirubin significantly influenced the maintenance tacrolimus dose. The tacrolimus-dosing model derived from linear regression model accounted for 40.5% of total variations in the tacrolimus maintenance dose.

CONCLUSIONS

A pharmacogenetics-based dosing model has been developed for the prediction of the tacrolimus maintenance dose in renal transplant recipients. This model may be useful in helping clinicians prescribe the initial tacrolimus dose with greater safety and effectiveness.

Simultaneous detection of CYP3A5 and MDR1 polymorphisms based on the SNaPshot assay

BACKGROUND

The 6986A>G polymorphism for CYP3A5 and the -129T>C, 1236C>T, 2677G>T/A, and 3435C>T polymorphisms for MDR1 are considered the major genetic factors affecting a range of drugs' metabolism and transport. Simultaneous genotyping of these five polymorphisms would be useful for estimating the therapeutic effects of their related drugs.

SUBJECTS AND METHODS

We have described a SNaPshot assay that can simultaneously detect all the five polymorphisms based on multiplex PCR and minisequencing reaction. A total of 168 unrelated Chinese DNA samples were used to establish and evaluate the assay.

RESULTS

The different genotypes of the five polymorphisms could be determined by peak retention time and colors. DNA sequencing was performed on samples randomly selected from each of the genotype groups detected by SNaPshot assay, and the results indicated 100% concordance.

CONCLUSION

The SNaPshot assay for the CYP3A5 and MDR1 five polymorphisms detection was accurate, automated, and cost-effective.