The Pharmacogenomics Journal (2012) 12, 255–259 & 2012 Macmillan Publishers Limited. All rights reserved 1470-269X/12 www.nature.com/tpj ORIGINAL ARTICLE Intuitive pharmacogenetics: spontaneous risperidone dosage is related to CYP2D6, CYP3A5 and ABCB1 genotypes S Mas1,2,3, P Gasso` 1,2,3, The aim of this study is to evaluate whether the quantitative prescription of ´ 1,2,3 4,2,3 risperidone (dosage) is related to the patient’s metabolic status. Metabolic SAlvarez , E Parellada , status was defined in terms of the most relevant polymorphisms of CYP2D6 4,5,2,3 M Bernardo and (*3, *4, *5, *6 and *1xN), CYP3A5 (*3A) and ABCB1 (G2677T) determined a A Lafuente1,2,3 posteriori and blinded to the clinicians. This prospective and observational study includes a cohort of 151 Caucasian psychiatric patients treated with 1Department of Pathological Anatomy, risperidone. Significant differences (Kruskal–Wallis test p ¼ 0.01) among the Pharmacology and Microbiology, University of doses administered were observed to correlate (Spearman’s r ¼ 1, p ¼ 0.02) Barcelona, Barcelona, Spain; 2Institut d’Investigacions Biome´diques August Pi i Sunyer with the different CYP2D6 groups. Poor metabolizers received the lowest (IDIBAPS), Barcelona, Spain; 3Centro de doses and ultra rapid metabolizers the highest. No significant correlations Investigacio´n Biome´dica en Red de Salud Mental were observed with regard to CYP3A5 and ABCB1. We find that, despite not 4 (CIBERSAM), Barcelona, Spain; Psychiatry knowing patients’ metabolic status, clinicians modify risperidone dosage in service, Hospital Clinic de Barcelona, Barcelona, Spain and 5Department of Psychiatry order to obtain the best therapeutic option. and Clinical Psychobiology, University of The Pharmacogenomics Journal (2012) 12, 255–259; doi:10.1038/tpj.2010.91; Barcelona, Barcelona, Spain published online 21 December 2010 Correspondence: Keywords: pharmacogenetics; risperidone; CYP2D6; CYP3A5; ABCB1; dose titration Dr A Lafuente, Department of Pathological Anatomy, Pharmacology and Microbiology, University of Barcelona, IDIBAPS, Casanova 143, E-08036 Barcelona, Spain. E-mail: [email protected] Introduction One of the most important issues regarding the variability of effect of antipsychotic drugs (AP) is the consequences of genetic variation in the regulators of drug metabolism. Concerning the metabolism of AP, the main metabolic pathway for many typical AP is CYP2D6, whereas for atypical AP, the most important CYPs are CYP3A4/A5, CYP2D6 and CYP1A2. CYP2D6 represents an average of 2% of hepatic CYP content and it is one of the best-known polymorphic drug-metabolizing enzymes with over 75 function- ally important allelic variants of CYP2D6 described to date (http://www.imm.ki. se/cypalleles). The CYP3A family, including CYP3A4, CYP3A5, CYP3A7 and CYP3A43, exhibits broad substrate specificity and metabolizes more than 50% of all pharmaceutical drugs.1 The CYP3A5 protein is polymorphically expressed in the liver and intestines, and several genetic variants have been identified (http:// www.imm.ki.se/cypalleles). Individuals with deficient CYP enzyme activity are classified as poor metabolizers (PM) and carry two detrimental CYP alleles. Individuals with slightly subnormal or normal rates of metabolism are defined as either intermediate metabolizers (IM; with only one functional copy) or Received 6 August 2010; revised 20 October 2010; accepted 16 November 2010; published extensive metabolizers (EM; with two functional copies of the gene), respectively. online 21 December 2010 Intermediate metabolizers have higher median metabolic ratios than homozygous Risperidone intuitive pharmacogenetics S Mas et al 256 EM. For CYP2D6, in addition, a subgroup of ultrarapid Hospital Clı´nic (Barcelona, Spain) over a period of 3 years metabolizers (UM) with extremely high enzyme activity can (2002À2004). In total, 151 subjects from this cohort be identified. (diagnosed following the DSM-IV criteria) treated with Risperidone is a widely used atypical AP for the treatment risperidone participated in this retrospective and observa- of schizophrenia and other psychotic disorders. It is tional study. A full description of this population can be extensively metabolized in the liver to a pharmacologically found in previous studies.12–16 active metabolite, 9-hydroxyrisperidone, mainly by cyto- chrome P450 2D6 (CYP2D6) and 3A (CYP3A4/3A5).2–4 Sample preparation and genotyping The antipsychotic effect of risperidone is assumed to The CYP2D6*3, *4, *5 and *6 genotypes were available for be related to the active moiety (the sum of risperidone most of the patients from previous studies.12 The newly and 9-hydroxyrisperidone), of which 9-hydroxyrisperidone included patients were genotyped using the methods constitutes the major part in plasma.5 Many in vivo and described previously.17 in vitro studies have revealed that CYP2D6 is primarily The CYP2D6 gene duplications (*1 Â N) were genotyped involved in risperidone metabolism.4 Polymorphic variants using TaqMan Copy Number Assays (assay ID Hs00010001_cn, of CYP2D6 have been shown to influence risperidone and Applied Biosystems, Foster City, CA, USA). 9-hydroxyrisperidone levels, although not the active moiety.6 The CYP3A5*3 allele and the ABCB1 (G2677T) poly- Several reports have recently suggested that CYP3A may be morphism were detected with real-time PCR by TaqMan substantially involved in the metabolism of risperidone.2 allelic discrimination pre-designed assays from Applied Bio- A polymorphic variant, CYP3A5*3, has been shown to systems according to the manufacturer’s guidelines (assay ID modulate the risperidone, 9-hydroxyrisperidone and active C__26201809_30 and C_11711720C_30, Applied Biosystems). moiety levels.6 Besides the P450 metabolizing enzymes, drug transporters Statistics are believed to affect risperidone pharmacokinetics. Data were analyzed using SPSS14.05 (statistical analysis P-glycoprotein is a member of the adenosine triphosphate- software, SPSS Inc., Chicago, IL, USA). Two-tailed P-values binding cassette (ABC) superfamily of transport proteins, o0.05 were considered to be of statistical significance. functioning as an efflux pump involved in drug absorption Means and s.d. were computed for continuous variables. and elimination.7 It has been reported that risperidone is Variables showing no normal distribution according to the a substrate of P-glycoprotein.8 Although it has not been Shapiro–Wilk test were compared with a non-parametric test studied in humans, it has been demonstrated in rats (Mann–Whitney U-test or Kruskal–Wallis test) and Spear- that risperidone crosses the blood–brain barrier more man’s rank correlation coefficients. Hardy–Weinberg equili- efficiently than 9-hydroxyrisperidone because of the effects brium and linkage disequilibrium analysis were performed of P-glycoprotein transport.9 Thus, P-glycoprotein seems to with the genetics package of the statistical software R (version pump 9-hydroxyrisperidone out of the brain more readily 2.4.0, www.r-project.org). than it pumps risperidone out. This may explain why plasma risperidone is more toxic than comparable plasma Results levels of 9-hydroxyrisperidone, even though they have similar affinities for the D2 receptor.10 A recent study The demographic and clinical characteristics of the patients showed that ABCB1 polymorphisms have a moderate effect are summarized in Table 1. The frequencies of the various on 9-hydroxyrisperidone and active moiety levels.11 metabolic phenotypes based on genotype categories According to our hypothesis, in an intuitive pharmaco- (CYP2D6 UM, EM, IM and PM; CYP3A5 EM, IM and PM) genetic exercise, clinicians (who are unaware of the patient’s and polymorphisms (ABCB1 (G2677T)) studied are also metabolic genotype) modify AP dosage via a trial and error shown in Table 1. All the polymorphisms analyzed were in strategy, in order to obtain the safest and most efficient Hardy–Weinberg equilibrium in cases and controls (data not treatment, and this will correspond with the patient’s shown). metabolic status. The aim of this study is to evaluate Figure 1 shows the mean daily dosage of risperidone in the whether the quantitative prescription of risperidone (do- different CYP2D6 (Figure 1a) and CYP3A5 (Figure 1b) sage) is related to the patient’s metabolic status (considering metabolic phenotypes. Significant differences among (Kruskal– the most relevant polymorphisms of CYP2D6 (*3, *4, *5, *6 Wallis test P ¼ 0.01) and correlation with (Spearman’s r ¼ 1, and *1xN), CYP3A5 (*3A) and ABCB1 (G2677T)), keeping in P ¼ 0.02) the dosage administered to the different CYP2D6 mind that genotyping was performed a posteriori as a part of groups were observed, with UM receiving the highest independent pharmacogenetic studies. risperidone dosage (8.8±5 mg per day, n ¼ 8), followed by EM (7.4±3 mg per day, n ¼ 90), IM (6.5±2 mg per day, n ¼ 37) and PM (5.9±2 mg per day, n ¼ 15). Post-hoc Patients and methods Bonferroni’s testing for pairwise comparisons between groups did not remain significant, probably because of the Participants small sizes of the PM and UM groups. Regarding CYP3A5, A cohort of 321 psychiatric inpatients receiving AP therapy although a trend could be observed with higher dosages for was recruited consecutively at the Psychiatry Service of the patients with higher metabolic activity (EM 7.3±3 mg per The Pharmacogenomics Journal Risperidone intuitive pharmacogenetics S Mas et al 257 Table 1 Demographic and clinical characteristics of the patients and frequencies of the various metabolic phenotypes based on the genotype categories (CYP2D6 UM, EM, IM and PM; CYP3A5 EM, IM, and PM) and polymorphisms studied (ABCB1 G2677T) N 151 Age (years, mean±s.d.) 35.9±14 Male N (%) 84 (55.6) Smokers N (%)a 59 (51.3) Diagnosis N (%) Schizophrenia and related disorders 118 (78.1) Bipolar disorders 27 (17.9) Other 6 (3.9) Risperidone dosage (mg/day, mean±s.d.) 7.2±2.5 CYP2D6 N (%)b PM 15 (9.9) IM 37 (24.5) EM 91 (60.3) UM 8 (5.3) CYP3A5 N (%)c PM 3 (2.0) IM 23 (15.5) EM 122 (82.4) ABCB1 G2677T N (%) GG 62 (41.3) GT 59 (39.3) TT 29 (19.3) Abbreviations: EM, extensive metabolizers; IM, intermediate metabolizers; PM, poor metabolizers; UM, ultrarapid metabolizers.