A systematic review and combined analysis of therapeutic drug monitoring studies for long-acting paliperidone

ABSTRACT

Introduction: This is a combined analysis of therapeutic drug monitoring (TDM) studies of long-acting injectable paliperidone formulations: monthly (PP1M) and three-month (PP3M) injections.

Areas covered: Fourteen PP1M articles and one PP3M article were identified. Using the paliperidone concentration/dose (C/D) ratio as a measure of clearance provided a weighted mean of 7.7 ng/ml per mg/day among 69 patients from three steady-state PP1M studies (twice as high as oral paliperidone). C/D ratios were: 1) higher by a factor of 1.26 in 12 geriatric patients, 2) lower in obese patients, and 3) 50% lower in three patients taking carbamazepine. No clinically meaningful PP3M pharmacokinetic data have been published.

Expert commentary: Half-life studies and more TDM PP1M studies using steady state are urgently needed. Early TDM studies may help orient PP1M dosing but steady state may not be reached until after the ninth injection (8 months). PP3M may take > 1 year to reach steady state. Any clinician considering switching patients to PP1M: 1) should switch from oral risperidone to PP1M rather than from oral paliperidone to PP1M, and 2) become proficient in paliperidone TDM to use during switches. TDM is highly recommended for patients with abnormal clearance (from obesity, geriatric age, or potent inducers).     

Pharmacokinetics of risperidone in different application forms – Comparing long-acting injectable and oral formulations

We aimed to explore the differences in the pharmacokinetics of risperidone between oral and long-acting injectable (LAI) formulations using a large database of therapeutic drug monitoring (TDM). Plasma concentrations of risperidone (RIS), its active metabolite (9-OH-RIS) and the active moiety (AM) (RIS+9-OH-RIS), their concentration-to-dose (C/D) ratios and ratio of RIS/9-OH-RIS (an index of CYP2D6 metabolic activity) were used to compare patients receiving risperidone orally (n = 851) and those treated with LAI RIS (n = 63). Patients taking CYP inducers or inhibitors or with liver/renal impairment were eliminated. Our study demonstrated that patients on LAI RIS, despite slightly higher RIS doses in the oral group, showed no significant differences in total AM or 9-OH-RIS. Conversely, RIS concentration, RIS C/D ratio and total C/D ratio were slightly higher in the LAI RIS group, reaching significance due to the large sample size. More importantly, the median ratio of RIS/9-OH-RIS was 0.52 in LAI RIS vs. 0.25 in the oral group, providing a significant difference (p < 0.001). After controlling for confounding factors, we replicated the RIS/9-OH–RIS ratio increases in patients with LAI RIS, probably reflecting a decrease in first-pass metabolism. More studies are required to establish the clinical use of TDM for patients on LAI RIS.     

A systematic review and combined analysis of therapeutic drug monitoring studies for oral paliperidone

Introduction: This article includes a combined analysis of therapeutic drug monitoring (TDM) studies and a review of the marketer’s data on pharmacological mechanisms.

Areas covered: An article search led to the inclusion of 21 paliperidone studies in the systematic review plus 2 case reports. Paliperidone clearance was calculated from: 1) steady-state studies using concentration/dose (C/D) ratios, and 2) single-dose studies describing 24-h area under the curve calculations. The marketed extended-release formulation has 28% bioavailability. Calculated mean C/D ratios (ng/ml/mg/d) were: 1) 4.09 in 6 studies of 221 non-Korean and non-geriatric adult patients, 2) 2.59 in 2 studies of 100 Korean adult patients, and 3) 6.89 in 1 study with 15 elderly Japanese patients. The limited drug–drug interaction studies indicated that carbamazepine is a clinically relevant inducer requiring three times the dosage, and that valproate, probably an inhibitor, requires half the dosage. Renal impairment markedly decreased paliperidone elimination, and other antipsychotics should be considered.

Expert Commentary: We recommend more use of: 1) paliperidone TDM in clinical practice, 2) TDM when moving from oral to long-acting paliperidone, 3) better designs for paliperidone TDM studies, 4) laboratory studies on paliperidone pharmacokinetic mechanisms, and 5) TDM studies comparing paliperidone and risperidone dosing.     

Effects of various CYP2D6 genotypes on the steady-state plasma concentrations of risperidone and its active metabolite, 9-hydroxyrisperidone,in Japanese patients with schizophrenia

The effects of various CYP2D6 genotypes on the steady-state plasma concentrations (Css) of risperidone and its active metabolite, 9-hydroxyrisperidone, were studied in 85 Japanese schizophrenic patients (27 men and 58 women) treated with 6 mg/d risperidone for at least 2 weeks. Plasma concentrations of risperidone and 9-hydroxyrisperidone were measured using liquid chromatography-tandem mass spectrometry. The patients had the following CYP2D6 genotypes: wild-type (wt)/wt (40 patients), CYP2D6*10 (*10)/wt ( 28), CYP2D6*5 (*5)/wt ( 8), *10/*10 ( 5), *5/*10 ( 3), and CYP2D6*4/CYP2D6*14 ( 1), respectively. The Css values of risperidone and 9-hydroxyrisperidone were corrected to the median body weight of 58 kg. The medians (ranges) of the Css of risperidone in the aforementioned genotype groups were 2.2 (0.37-35.7), 6.4 (2.1-26.5), 12.3 (4.7-39.5), 19.4 (13.4-26.4), 64.0 (41.6-68.8), and 91.8 nmol/L. Those values for risperidone-to-9-hydroxyrisperidone ratio were 0.03 (0.01-0.33), 0.06 (0.03-0.19), 0.14 (0.07-0.29), 0.28 (0.25-0.38), 0.48 (0.38-0.58), and 2.35, respectively. The Css of risperidone was significantly (P < 0.05 or P < 0.001) different among the four genotype groups (wt/wt, *10/wt, *5/wt, and *10/*10), except between the *5/wt and *10/*10 groups. Also, the risperidone-to-9-hydroxyrisperidone ratio significantly (P < 0.005 or P < 0.001) differed among these genotype groups. No significant differences were found in the Css of 9-hydroxyrisperidone and the active moiety (the Css of risperidone plus 9-hydroxyrisperidone) among these genotype groups. This study confirms previous findings that the CYP2D6 status affects the Css of risperidone via its strong regulation of 9-hydroxylation of risperidone. However, similar active moiety of risperidone among different genotype groups suggests that the determination of the CYP2D6 genotype has little importance for clinical situations.     

Effects of CYP2D6 genotypes on plasma concentrations of risperidone and enantiomers of 9-hydroxyrisperidone in Japanese patients with schizophrenia

It has been shown that risperidone (+)-9-hydroxylation is enantioselectively catalyzed by the polymorphic CYP2D6 in human liver. This study aimed to examine the effect of CYP2D6 genotype on (+)-9-hydroxylation of risperidone in schizophrenic patients. Subjects were 38 Japanese schizophrenic inpatients receiving 6 mg/day of risperidone. Plasma concentrations of risperidone and (+)- and (-)-9-hydroxyrisperidone at steady state were quantified using LC/MS/MS and HPLC with alpha 1 acid-AGP chiral column, respectively. The CYP2D6*5(*5) and *10 alleles were identified using polymerase chain reaction (PCR) methods. Twenty patients had no mutated allele, 14 had one mutated allele, and 4 had two mutated alleles. There were significant differences in the steady-state plasma concentrations of risperidone (ANOVA; p < 0.0001) among the three genotype groups, while the CYP2D6 genotype did not affect the steady-state plasma concentrations of (+)-9-hydroxyrisperidone (p = 0.314) or (-)-9-hydroxyrisperidone (p = 0.957). The concentration ratio of risperidone to 9-hydroxyrisperidone was strongly dependent on the CYP2D6 genotypes. This study suggests that CYP2D6 activity strongly influences the steady-state plasma concentrations of risperidone and risperidone/9-hydroxyrisperidone concentration ratios but is unlikely to determine enantio-selectivity in the steady-state plasma concentrations of 9-hydroxyrisperidone in the clinical situation.     

Risperidone metabolic ratio as a biomarker of individual CYP2D6 genotype in schizophrenic patients

Purpose

The purpose of the present study was to investigate the predictive value of the risperidone metabolic ratio for the individual CYP2D6 genotype.

Methods

The determination of risperidone, 9-hydroxyrisperidone, and CYP2D6 genotype was performed in 89 schizophrenic patients. The receiver operator characteristic (ROC) method and the area under the ROC curve (AUC) were used to illustrate the predictive value of risperidone metabolic ratio for the individual CYP2D6 genotype. The area under the ROC curve (AUC) was used as a global measure of this predictive value. To evaluate the proposed cutoff levels of >1 and <0.1 to identify individuals with a poor or ultrarapid CYP2D6 genotype the sensitivity, specificity, positive predictive value and negative predictive were calculated.

Results

The area under the ROC curve (AUC) for poor and ultrarapid metabolisers was 0.85 and 0.86, respectively. The sensitivity, specificity, positive predictive value and negative predictive value of a risperidone/9–OH-risperidone ratio >1 to CYP2D6 poor metaboliser genotype were 75 %, 95 %, 60 % and 97 %, respectively. The corresponding measures for a metabolic ratio?<?0.1 to predict ultrarapid metabolisers were 80 %, 77 %, 18 % and 98 %.

Conclusions

A metabolic ratio?>?1 or?<?0.1 may be a useful therapeutic biomarker to recommend CYP2D6 genetic testing to guide the present or future treatment of patients in need of psychotropic drugs.     

Effects of various factors on steady-state plasma concentrations of risperidone and 9-hydroxyrisperidone: lack of impact of MDR-1 genotypes

AIMS: An in vitro study has suggested that risperidone is a substrate of P-glycoprotein, which is coded by MDR-1 gene. Thus, we studied the effects of major polymorphisms of the MDR-1 gene on plasma drug concentrations. METHODS: Subjects were 85 schizophrenic patients receiving 3 mg twice daily of risperidone. Sample collections were conducted 12 h after the bedtime dosing. Plasma concentrations of risperidone and 9-hydroxyrisperidone were quantified using LC/MS/MS. MDR-1 genotypes (C3435T and G2677T/A) and CYP2D6 genotypes were identified using PCR-RFLP methods. RESULTS: There was no difference in geometric mean (95% CI) of steady-state plasma concentration of risperidone between C3435T genotypes [C/C, C/T, T/T; 2.06 (1.63, 6.47), 2.96 (3.10, 7.91), 2.28 (1.81, 8.04) ng ml(-1), P = 0.759] or G2677T/A genotypes [G/G, G/T or A, T or A/T or A; 1.62 (0.08, 6.07), 2.64 (3.25, 7.10), 2.71 (2.77, 8.72) ng ml(-1), P = 0.625] or 9-hydroxyrisperidone between C3435T genotypes [38.3 (33.7, 50.1), 34.9 (32.9, 42.0), 35.7 (31.7, 42.3) ng ml(-1), P = 0.715] or G2677T/A genotypes [40.6 (33.0, 51.8), 35.0 (33.3, 42.4), 36.1 (32.8, 47.2) ng ml(-1), P = 0.601]. Multiple regression analyses including CYP2D6 genotypes, sex, and age revealed that steady-state plasma concentration of risperidone correlated with the number of mutated alleles for CYP2D6 (standardized partial correlation coefficients (beta) = 0.540, P < 0.001) and those of 9-hydroxyrisperidone (standardized beta = 0.244, P = 0.038) and active moiety (standardized beta = 0.257, P = 0.027) correlated with age. CONCLUSIONS: These findings suggest that the MDR-1 variants are not associated with steady-state plasma concentration of risperidone or 9-hydroxyrisperidone, but CYP2D6 genotypes and age are determinants of these concentrations.     

Population Pharmacokinetics of Risperidone and 9-Hydroxyrisperidone in Patients with Acute Episodes Associated with Bipolar I Disorder

A population model was developed with the aim to simultaneously describe risperidone and 9-hydroxyrisperidone pharmacokinetics; to obtain estimates for pharmacokinetic parameters and associated inter- and intra-individual variability of risperidone and 9-hydroxyrisperidone; and to evaluate the influence of patient demographic characteristics and other factors on risperidone, 9-hydroxyrisperidone, and active moiety pharmacokinetics. Data were obtained from 407 patients enrolled in four Phase 1 (serial blood sampling) and three Phase 3 trials (sparse sampling), representing dosage regimens ranging from 4 mg single dose to flexible 1–6 mg once daily. A pharmacokinetic model with two-compartment submodels for risperidone and 9-hydroxyrisperidone disposition and a sequential zero- and first-order absorption pathway was selected based on prior knowledge. A mixture model was incorporated due to CYP2D6 polymorphism of risperidone conversion to 9-hydroxyrisperidone. Patient characteristics tested as potential covariates were: age, sex, race, body weight, lean body mass, body mass index, creatinine clearance, liver function laboratory parameters, study, and carbamazepine comedication. The quasi-clearance of active moiety (the sum of risperidone and 9-hydroxyrisperidone) was simulated and linear regression performed to identify significant covariates. The selected pharmacokinetic model described the plasma concentration-time profiles for risperidone and 9-hydroxyrisperidone quite well and was able to determine each patient’s phenotype. Covariates significantly affecting the pharmacokinetics were carbamazepine comedication, and study because the proportion of patients assigned to the intermediate metabolizer status decreased from single to multiple dosing while the proportion assigned to extensive metabolizer status increased. Covariates with limited and clinically irrelevant effects on active moiety concentrations were patient phenotype, race, and total protein. Carbamazepine also decreased active moiety concentrations.     

Population pharmacokinetic analysis of risperidone and 9-hydroxyrisperidone with genetic polymorphisms of CYP2D6 and ABCB1

This study estimated the population pharmacokinetics of risperidone and its active metabolite, 9-hydroxyrisperidone, according to genetic polymorphisms in the metabolizing enzyme (CYP2D6) and transporter (ABCB1) genes in healthy subjects. Eighty healthy subjects who received a single oral dose of 2?mg risperidone participated in this study. However, eight subjects with rare genotype variants in CYP2D6 alleles were excluded from the final model built in this study. We conducted the population pharmacokinetic analysis of risperidone and 9-hydroxyrisperidone using a nonlinear mixed effects modeling (NONMEM) method and explored the possible influence of genetic polymorphisms in CYP2D6 alleles and ABCB1 (2677G>T/A and 3435C>T) on the population pharmacokinetics of risperidone and 9-hydroxyrisperidone. A two-compartment model with a first-order absorption and lag time fitted well to serum concentration-time curve for risperidone. 9-hydroxyrisperidone was well described by a one-compartment model as an extension of the parent drug (risperidone) model with first-order elimination and absorption partially from the depot. Significant covariates for risperidone clearance were genetic polymorphisms of CYP2D6*10, including CYP2D6*1/*10 (27.5?% decrease) and CYP2D6*10/*10 (63.8?% decrease). There was significant difference in the absorption rate constant (k ( a )) of risperidone among the CYP2D6*10 genotype groups. In addition, combined ABCB1 3435C>T and CYP2D6*10 genotypes had a significant (P?T as covariates was successfully constructed. The estimated contribution of genetic polymorphisms in CYP2D6*10 and ABCB1 3435C>T to population pharmacokinetics of risperidone and 9-hydroxyrisperidone suggests the interplay of CYP2D6 and ABCB1 on the pharmacokinetics of risperidone and 9-hydroxyrisperidone according to genetic polymorphisms.     

Cytochrome P450 2D6 genotype and steady state plasma levels of risperidone and 9-hydroxyrisperidone

The role of the polymorphic cytochrome P450 2D6 (CYP2D6) in the metabolism of risperidone to its major active metabolite, 9-hydroxyrisperidone (9-OH-risperidone), has been documented after single oral doses of the drug. In this study, the influence of the CYP2D6 polymorphism on the steady-state plasma concentrations of risperidone and 9-OH-risperidone was investigated. Thirty-seven schizophrenic patients on monotherapy with risperidone, 4–8 mg/day, were genotyped by RFLP and PCR for the major functional variants of the CYP2D6 gene. Steady state plasma levels of risperidone and 9-OH-risperidone were analysed by HPLC. Based on the genotype analysis, three patients were classified as ultrarapid metabolizers (UM) with an extra functional CYP2D6 gene, 16 were homozygous extensive metabolizers (EM), 15 heterozygous EM and three poor metabolizers (PM). The median steady-state plasma concentration-to-dose (C/D) ratios of risperidone were 0.6, 1.1, 9.7 and 17.4 nmol/l per mg in UM, homozygous EM, heterozygous EM and PM, respectively, with statistically significant differences between PM and the other genotypes (P<0.02). The C/D of 9-OH-risperidone also varied widely but was not related to the genotype. The risperidone/9-OH-risperidone ratio was strongly associated with the CYP2D6 genotype, with the highest ratios in PM (median 0.79). Heterozygous EM also had significantly higher ratios than homozygous EM (median value 0.23 versus 0.04; P<0.01) or UM (median 0.03; P<0.02). No significant differences were found in the C/D of the sum of the plasma concentrations of risperidone and 9-OH-risperidone between the genotype groups. In conclusion, the steady-state plasma concentrations of risperidone and the risperidone/9-OH-risperidone ratio are highly dependent on the CYP2D6 genotype. However, as risperidone and 9-OH-risperidone are considered to have similar pharmacological activity, the lack of relationship between the genotype and the sum of risperidone and 9-OH-risperidone indicates that the CYP2D6 polymorphism may be of limited importance for the clinical outcome of the treatment. Received: 3 March 1999 / Final version: 28 June 1999     

ABCB1 polymorphisms influence steady-state plasma levels of 9-hydroxyrisperidone and risperidone active moiety

Risperidone is metabolized to its active metabolite, 9-hydroxyrisperidone, mainly by the cytochrome P450 enzymes CYP2D6 and 3A4. Its antipsychotic effect is assumed to be related to the active moiety, that is, the sum of risperidone and 9-hydroxyrisperidone. Both risperidone and 9-hydroxyrisperidone are substrates of P-glycoprotein (P-gp), a transport protein involved in drug absorption, distribution, and elimination. The aim of the present study was to evaluate the influence of polymorphisms in genes encoding CYP3A5 and P-gp (ABCB1) on the steady-state plasma levels of risperidone, 9-hydroxyrisperidone, and the active moiety, taking CYP2D6 genotype status into account. Forty-six white patients with schizophrenia treated with risperidone (1-10 mg/d) in monotherapy for 4-6 weeks were genotyped, and their plasma concentrations of risperidone and 9-hydroxyrisperidone were measured. Dose-corrected plasma concentrations (C/D) of risperidone, 9-hydroxyrisperidone, and active moiety showed up to 68-, 9-, and 10-fold interindividual variation, respectively. Six patients carried 1 CYP3A5*1 allele and therefore were likely to express the CYP3A5 enzyme. The CYP3A5 genotype did not influence risperidone, 9-hydroxyrisperidone, or active moiety C/Ds. The CYP2D6 genotype in these 46 patients was again associated with risperidone C/D (P = 0.001) but not with 9-hydroxyrisperidone C/D or active moiety C/D, as previously shown by our group in 37 of these patients. Patients homozygous for the ABCB1 3435T/2677T/1236T haplotype had significantly lower C/Ds of 9-hydroxyrisperidone (P = 0.026) and active moiety (P = 0.028) than patients carrying other ABCB1 genotypes. In conclusion, our results confirmed the significant effect of CYP2D6 genotype on the steady-state plasma levels of risperidone and showed that ABCB1 polymorphisms have a moderate effect on those of 9-hydroxyrisperidone and the active moiety.     

Prolactin release in children treated with risperidone: impact and role of CYP2D6 metabolism

OBJECTIVE: Little is known about the role of CYP2D6 polymorphism in risperidone-induced prolactin release in children. METHOD: Twenty-five children (aged 5-15 years) with pervasive developmental disorders were genotyped for CYP2D6 polymorphisms. Serum prolactin, risperidone, and 9-hydroxyrisperidone were assessed at baseline and after 8 weeks of risperidone treatment (mean dosage, 0.06 +/- 0.03 mg/kg/d). After 24 weeks of treatment, prolactin was measured in a subsample of 15 children. Adverse effects were evaluated using a clinician-rated survey. RESULTS: Mean +/- SD prolactin levels increased from 7.8 +/- 8.0 ng/mL at baseline to 33.2 +/- 12.8 ng/mL at week 8 (P < 0.001), with a slight decrease to 28.8 +/- 13.6 ng/mL at week 24. At week 8, serum prolactin level was positively correlated with dose per kilogram (r = 0.648, P < 0.001), number of functional CYP2D6 genes (J = 2.117, P = 0.034), and serum 9-hydroxyrisperidone concentration (r = 0.664, P = 0.001) and was negatively correlated with the risperidone/9-hydroxyrisperidone ratio (r = -0.571, P = 0.004) but not with risperidone concentration (r = -0.243, P = 0.264) nor age (r = 0.072, P = 0.733). Prolactin elevation was not associated with adverse effects. CONCLUSIONS: Low-to-intermediate doses of risperidone induced a 4-fold prolactin increase in children without a clear development of tolerance up to 6 months. CYP2D6 ultrarapid metabolism may be a risk factor for more pronounced prolactin elevation.     

细胞色素P4502D6酶基因多态性与利培酮代谢的相关性研究

目的 研究利培酮(抗精神分裂症药)在人体代谢过程与CYP2D6*10基因多态性的关系.方法 不同CYP2D6*1/*1(n=5)、*1/*10(n=12)及*10/*10(n=6)基因型的健康志愿者,单次口服利培酮2 mg后,用LC-MS/MS方法测定血浆中利培酮及其活性代谢产物9-羟基利培酮浓度,研究利培酮药代动力学与CYP2D6*10基因型的相关性.结果 CYP2D6*10/*10和CYP2D6*1/*10基因型与CYP2D6*1/*1基因型的受试者相比,利培酮的AUC0-∞分别增加811%和212%,2者比较差异非常显著(P<0.001);利培酮/9-羟基利培酮的AUC比值在各CYP2D6*10基因型间存在显著性差异(P<0.001).结论 CYP2D6*10 C188T突变使CYP2D6对利培酮的代谢活性降低,体内利培酮暴露量增加.     

Significant pharmacokinetic interaction between risperidone and carbamazepine: its relationship with CYP2D6 genotypes

The effects of carbamazepine coadministration (400 mg/day for 1 week) on plasma concentrations of risperidone and its active metabolite 9-hydroxyrisperidone were studied in 11 schizophrenic inpatients treated with 6 mg/day risperidone. Blood samplings were performed before and during carbamazepine coadministration, and 1 week after its discontinuation. Plasma concentrations of risperidone and 9-hydroxyrisperidone were measured using liquid chromatography-mass spectrometry-mass spectrometry. CYP2D6 genotypes were determined using the polymerase chain reaction method. Plasma concentrations of risperidone and 9-hydroxyrisperidone during carbamazepine coadministration (2.5+/-3.6 ng/ml and 19.4+/-4.1 ng/ml) were significantly ( P<0.01) lower than those before carbamazepine coadministration (5.0+/-7.9 ng/ml and 34.6+/-9.8 ng/ml). The changes in risperidone concentrations were positively correlated to the concentration ratios of risperidone/9-hydroxyrisperidone (r(s)=0.90, P<0.01), which were closely associated with CYP2D6 genotypes. The present study suggests that carbamazepine induces the metabolism of risperidone and 9-hydroxyrisperidone, and that the decrease in risperidone concentration is dependent on the CYP2D6 activity.     

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.     

Different enantioselective 9-hydroxylation of risperidone by the two human CYP2D6 and CYP3A4 enzymes.

The antipsychotic agent risperidone, is metabolized by different cytochrome P-450 (CYP) enzymes, including CYP2D6, to the active 9-hydroxyrisperidone, which is the major metabolite in plasma. Two enantiomers, (+)- and (-)-9-hydroxyrisperidone might be formed, and the aim of this study was to evaluate the importance of CYP2D6 and CYP3A4/CYP3A5 in the formation of these two enantiomers in human liver microsomes and in recombinantly expressed enzymes. The enantiomers of 9-hydroxyrisperidone were analyzed with high pressure liquid chromatography using a chiral alpha-1 acid glycoprotein column. A much higher formation rate was observed for (+)-9-hydroxyrisperidone than for (-)-9-hydroxyrisperidone in microsomes prepared from six individual livers. The formation of (+)-9-hydroxyrisperidone was strongly inhibited by quinidine, a potent CYP2D6 inhibitor, whereas ketoconazole, a CYP3A4 inhibitor, strongly inhibited the formation of (-)-9-hydroxyrisperidone. Recombinant human CYP2D6 produced only (+)-9-hydroxyrisperidone, whereas a lower formation rate of both enantiomers was detected with expressed CYP3A4 and CYP3A5. In vivo data from 18 patients during treatment with risperidone indicate that the plasma concentration of the (+)-enantiomer is higher than that of the (-)-enantiomer in extensive metabolizers of CYP2D6. These findings clearly suggest that CYP2D6 plays a predominant role in (+)-9-hydroxylation of risperidone, the major metabolic pathway in clinical conditions, whereas CYP3A catalyzes the formation of the (-)-9-hydroxymetabolite. Further studies are required to evaluate the pharmacological/toxic activity of both enantiomers.     

Risperidone metabolism in relation to CYP2D6*10 allele in Korean schizophrenic patients

OBJECTIVE: Risperidone is known to be biotransformed to its active metabolite, 9-hydroxyrisperidone, by the polymorphic CYP2D6 in Caucasians. This study aimed to investigate the relationship between the CYP2D6*10 allele and the plasma levels of risperidone and 9-hydroxyrisperidone in Korean schizophrenic patients. METHODS: Eighty-two Korean schizophrenic patients in monotherapy with oral doses of risperidone from 1 mg/day to 8 mg/day (mean +/- SD 4.3 +/- 1.9, median 4) participated in this study. Plasma concentrations of risperidone and 9-hydroxyrisperidone were analyzed using high-performance liquid chromatography. The CYP2D6*10 allele, which contains C188T mutation in exon 1, was identified using allele-specific polymerase chain reaction amplification. RESULTS: Seventeen of 82 patients were homozygous for CYP2D6*1, 22 for *10, while the remaining 43 patients were heterozygous for these alleles. The plasma levels of risperidone and 9-hydroxyrisperidone ranged from 1.0 nM to 168 nM and 6.2 nM to 235 nM, respectively. The median concentrations/dose (C/Ds) (range) of risperidone in CYP2D6*1/*1, *1/*10, and *10/*10 groups were 1.7 (0.2-7.9), 2.6 (0.3-27.1), and 6.7 nM/mg (2.4-21.0), respectively. There was a statistically significant difference among the three genotypes (Kruskal-Wallis test, P<0.001). For 9-hydroxyriperidone, the corresponding median C/Ds were 13.1 (3.3-25.4), 11.9 (4.2-30.8), and 13.6 nM/mg (6.5-52.8), respectively, with no significant difference between the genotypes (P=0.54). The medians of the ratios between risperidone and 9-hydroxyrisperidone concentrations were 0.13 (0.01-0.93), 0.28 (0.01-2.77), and 0.46 nM/mg (0.05-1.28) in *1/*1, *1/*10, and *10/*10 genotypes, respectively, and they were significantly different (P=0.004). The active moieties (sum of the C/Ds of risperidone and 9-hydroxyrisperidone) were not significantly different between the genotypes (P=0.063). CONCLUSION: In Korean schizophrenic patients, the metabolism of risperidone is dependent on CYP2D6, and the CYP2D6*10 allele is important for the regulation of the activity of this enzyme. There were no significant differences in the plasma concentration of parent drug plus its active metabolite between the genotypes. This suggests that the clinical significance of this polymorphism is limited. Our study confirms previous studies on risperidone metabolism in Caucasians.     

Serum prolactin levels, plasma risperidone levels, polymorphism of cytochrome P450 2D6 and clinical response in patients with schizophrenia

The object of this study is to assess 1) the relationship between plasma antipsychotic drug concentration, serum prolactin levels and the clinical efficacy of risperidone, 2) the relationship between the CYP2D6 polymorphisms and metabolizing of risperidone and 3) the role of 9-hydroxyrisperidone in elevating prolactin levels. One-hundred and eighteen Chinese schizophrenia patients (40 males, 78 females, age 15-60 years) were given risperidone at dosages ranging from 2-8 mg/day for 8 weeks. Clinical efficacy was determined using the Brief Psychiatric Rating Scores (BPRS). Serum prolactin levels were assayed before and after the 8 week treatment and plasma risperidone and 9-hydroxyrisperidone levels were also measured at the end of the 8-week treatment. The results showed there was no significant correlation between the concentration of active moiety and clinical response. Risperidone treatment significantly increased serum prolactin levels. Furthermore, changes of prolactin levels were not correlated with the clinical response. For the risperidone/ 9-hydroxyrisperidone ratio, there was a statistically significant difference among the CYP2D6*1/*1, *1/*10, *10/*10 genotypes (Kruskal-Wallis test, p = 0.012). No significant differences were found in the concentration of 9-hydroxyrisperidone and active moiety among the genotypes. In addition, the concentration of 9-hydroxyrisperidone was not significantly correlated with the increase of serum prolactin. In conclusion, our study has, for the first time, produced evidence that in Chinese schizophrenic patients, the metabolism of risperidone is dependent on CYP2D6. Neither changes in serum prolactin levels nor plasma concentration of active moiety were significantly correlated with clinical efficacy of risperidone. 9-hydroxyrisperidone may not play a predominant role in elevating serum prolactin level.     

The role of cytochrome P450 enzymes in the metabolism of risperidone and its clinical relevance for drug interactions

In the recent years it has been increasingly recognized that pharmacogenetical factors play an important role in the drug treatment. These factors may influence the appearance of side-effects and drug interactions due to interindividual differences in the activity of metabolizing enzymes. Risperidone in humans is mainly metabolized to 9-hydroxyrisperidone by the polymorphic cytochrome enzyme P450 2D6 (CYP2D6). Plasma concentrations of risperidone and 9-hydroxyrisperidone show large interindividual variability, which may be partly related to the activity of the CYP2D6 enzyme. Around seven percent of Caucasians have a genetically inherited impaired activity of the CYP2D6 enzyme. Debrisoquine metabolic ratio (a marker of CYP2D6 activity) and the number of CYP2D6 active genes have been related to risperidone plasma concentrations among patients during steady-state conditions. A large number drugs have been described to be metabolized by CYP2D6, and it is therefore important to evaluate the clinical significance of the impaired metabolism and possible drug interactions on the enzyme. Since risperidone/9-hydroxyrisperidone ratio strongly correlates with CYP2D6 enzyme activity and the number of CYP2D6 active genes, thus it might be a useful tool in clinical practice to estimate the possible risk of drug interactions due to impaired CYP2D6 enzyme activity. CYP3A4 is the most abundant drug metabolizing enzyme in humans, and in vitro and in vivo results suggest also a role for the enzyme in risperidone metabolism. The consideration of the implication of cytochrome P450 enzymes in risperidone metabolism may help to individualize dose schemes in order to avoid interactions and potentially dangerous side-effects, such us QTc interval lengthening among patients with cardiac risk factors.     

LC-MS/MS法测定人血浆中利培酮和9-羟基利培酮的浓度及临床应用

目的：建立简单快速的液相串联质谱法（LC-MS/MS）测定人血浆中利培酮及其代谢物9-羟基利培酮的浓度。方法：血浆样本采用甲醇沉淀蛋白法处理,以地西泮为内标,采用ES Industries Sonoma C₁₈（2）色谱柱（100 mm×2.1 mm,3 μm）分离化合物;流动相包括A-50%甲醇水溶液（含6 mmol·L^-1乙酸铵）、B-0.1%甲酸乙腈溶液;梯度洗脱,总流速0.60 mL·min^-1;进样量10 μL;柱温30℃。采用正离子MRM模式扫描,电喷雾电离,利培酮、9-羟基利培酮及地西泮内标离子通道分别为m/z411.3→m/z191.1、m/z427.2→m/z207.0和m/z285.1→m/z193.1。依据《中国药典》（2015年版）通则中9012"生物样品定量分析方法验证指导原则"对所建方法进行验证。结果：利培酮在0.16~101.40 μg·L^-1的浓度范围内线性关系良好（r>0.999）,9-羟基利培酮在0.40~256.80 μg·L^-1浓度范围内线性关系良好（r>0.999）;在定量下限,低、中、高浓度批内与批间精密度的标准偏差（RSD）均小于10.9%,准确度符合要求;含分析物血浆样品在不同储存条件下结果稳定。该法已成功应用于临床样本治疗药物监测。运用此方法监测分析一千多份临床样本得出总利培酮临床实际测定浓度范围为13.30~93.22 μg·L^-1。结论：本研究建立了测定血浆中利培酮及其代谢物9-羟基利培酮浓度的快速、简便、实用的LC-MS/MS方法。利培酮临床实际测定浓度范围相比于神经精神药理学与药物精神病学协会专家组推荐治疗浓度范围更宽,且多次监测的患者中女性血药浓度相对于男性更趋于稳定。