Pharmacodynamic Genes Research Articles

Pharmacogenomics study in a Taiwanese methadone maintenance cohort

Pharmacogenomics is the study of drug treatment responses in subgroups of patients on the basis of their genetic variants or genetic expression information. In 2006, the government of Taiwan launched a methadone maintenance treatment program, which is usually prescribed for patients with heroin dependence. In this study, 366 patients who had taken methadone continually in the previous 7 days were examined. Data from the Treatment Outcomes Profile (TOP), Severity of Dependence Scale (SDS), Clinical Opioid Withdrawal Scale (COWS), and Treatment Emergent Symptoms Scale (TESS) were obtained from the patients' report records. The genes CYP2B6, CYP3A4, and CYP2C19—which encode the liver cytochrome P-450 (CYP) enzymes that are involved in the metabolism of methadone—were selected and genotyped in this cohort. We found that single nucleotide polymorphisms (SNPs) on the CYP2B6 gene were associated with the plasma S-methadone concentration. The SNPs on the CYP3A4 gene were associated with withdrawal symptoms and side effects. The SNPs on the CYP2C19 gene were associated with the methadone dose. The SNPs in the genes (e.g., UGT2B7) encoding the morphine phase II metabolic enzyme were associated with the withdrawal symptom scores. In pharmacodynamic genes, the SNPs on the OPRM1 gene were associated with the side effects of insomnia and change in libido. We conclude that SNP markers may be useful in the future for adjusting methadone dosage and for reducing adverse reactions.

Clinical validity of cytochrome P450 metabolism and serotonin gene variants in psychiatric pharmacotherapy

Adverse events, response failures and medication non-compliance are common in patients receiving medications for the treatment of mental illnesses. A systematic literature review assessed whether pharmacokinetic (PK) or pharmacodynamic (PD) responses to 26 commonly prescribed antipsychotic and antidepressant medications, including efficacy or side effects, are associated with nucleotide polymorphisms in eight commonly studied genes in psychiatric pharmacotherapy: CYP2D6, CYP2C19, CYP2C9, CYP1A2, CYP3A4, HTR2C, HTR2A, and SLC6A4. Of the 294 publications included in this review, 168 (57%) showed significant associations between gene variants and PK or PD outcomes. Other studies that showed no association often had insufficient control for confounding variables, such as co-medication use, or analysis of medications not substrates of the target gene. The strongest gene–outcome associations were for the PK profiles of CYP2C19 and CYP2D6 (93% and 90%, respectively), for the PD associations between HTR2C and weight gain (57%), and for SLC6A4 and clinical response (54%), with stronger SLC6A4 response associations for specific drug classes (60–83%). The preponderance of evidence supports the validity of analyzing nucleotide polymorphisms in CYP and pharmacodynamic genes to predict the metabolism, safety, or therapeutic efficacy of psychotropic medications commonly used for the treatment of depression, schizophrenia, and bipolar illness.

Pharmacogenetics of mood disorders: what clinicians need to know

Pharmacogenetics brought the promise of matching individuals with treatments that would be efficacious while minimizing adverse events. This has been long needed in psychiatry, where treatment options have been empirical and treatment choices have been made largely based on clinical judgment. The efficacy and tolerability of antidepressants, the most common drugs used in mood disorders, have been widely studied in pharmacogenetics. Genetic association studies have been reported for pharmacokinetic genes such as the CYP450 isoenzymes or MDR1, and pharmacodynamic genes such as the serotonin transporter (SLC6A4) or the serotonin 2A receptor (HTR2A). However, despite the large number of reports, clinically useful predictors are still scarce for antidepressant monotherapy. Pharmacogenetic predictors of efficacy for mood stabilizers such as lithium and anticonvulsants have not had a dissimilar fate, and clinically meaningful markers are yet to emerge. The lack of consistent results may be in part due to small samples of heterogeneous populations and lack of consensus on phenotype definitions. Current pharmacogenetic recommendations include testing for HLA-B*1502 when using carbamazepine in Asian ancestry populations to prevent Stevens–Johnson syndrome, CYP2D6 genotypes when using pimozide, and CYP2D6 in polypharmacy to minimize drug interactions. This review, which is aimed at clinicians, lays the basis for understanding strengths and weaknesses of pharmacogenetic studies and outlines current clinical uses of these biomarkers.

PharmGKB summary

Thorn, Caroline F.; Ellison, David H.; Turner, Stephen T.; Altman, Russ B.; Klein, Teri E. Author Information

Pharmacodynamic Genetic Variants Related to Antipsychotic Adverse Reactions in Healthy Volunteers

Clinical trials with healthy volunteers are a useful model for evaluating safety and tolerability, without the interference of concomitant diseases and drugs. The present study aims to improve our understanding of antipsychotic-related adverse reactions (ARs) and their possible association with common genetic variants of pharmacodynamic proteins such as neurotransmitter receptors/transporters. A total of eight polymorphisms located in seven pharmacodynamic-related genes (SCL6A4, MDR1, 5HT2A, DRD2, DRD3, COMT and GRIN2B) were genotyped in a cohort of 211 healthy volunteers who received a single dose of risperidone (1 mg), olanzapine (5 mg) or quetiapine (25 mg). Interestingly, a significant association was found between the incidence of neurological ARs and specific polymorphisms in key genes (DRD2 and SCL6A4). Genetic variants in pharmacodynamic genes could represent valuable markers of AR risk and antipsychotic safety. Original submitted 7 February 2013; Revision submitted 3 June 2013.

Germline Pharmacogenetics of Paclitaxel for Cancer Treatment

Paclitaxel is a highly effective chemotherapeutic agent used in a variety of solid tumors. Some paclitaxel-treated patients experience the intended therapeutic response with manageable side effects, while others have minimal response and/or severe toxicity. This variability in treatment outcome is partially determined by variability in drug exposure (pharmacokinetics) and by patient and tumor sensitivity (pharmacodynamics). Both pharmacokinetics and pharmacodynamics are dictated in part by common variants in the germline genome, known as SNPs. This article reviews the published literature on paclitaxel pharmacogenetics in cancer, focusing primarily on polymorphisms in genes relevant to paclitaxel pharmacokinetics and discusses preliminary work on pharmacodynamic genes and genome-wide association studies.

Role of aldo-keto reductases and other doxorubicin pharmacokinetic genes in doxorubicin resistance, DNA binding, and subcellular localization

BackgroundSince proteins involved in chemotherapy drug pharmacokinetics and pharmacodynamics have a strong impact on the uptake, metabolism, and efflux of such drugs, they likely play critical roles in resistance to chemotherapy drugs in cancer patients.MethodsTo investigate this hypothesis, we conducted a whole genome microarray study to identify difference in the expression of genes between isogenic doxorubicin-sensitive and doxorubicin-resistant MCF-7 breast tumour cells. We then assessed the degree of over-representation of doxorubicin pharmacokinetic and pharmacodynamic genes in the dataset of doxorubicin resistance genes.ResultsOf 27,958 Entrez genes on the array, 7.4 per cent or 2,063 genes were differentially expressed by ≥ 2-fold between wildtype and doxorubicin-resistant cells. The false discovery rate was set at 0.01 and the minimum p value for significance for any gene within the “hit list” was 0.01. Seventeen and 43 per cent of doxorubicin pharmacokinetic genes were over-represented in the hit list, depending upon whether the gene name was identical or within the same gene family, respectively. The most over-represented genes were within the 1C and 1B families of aldo-keto reductases (AKRs), which convert doxorubicin to doxorubicinol. Other genes convert doxorubicin to other metabolites or affect the influx, efflux, or cytotoxicity of the drug. In further support of the role of AKRs in doxorubicin resistance, we observed that, in comparison to doxorubicin, doxorubincol exhibited dramatically reduced cytotoxicity, reduced DNA-binding activity, and strong localization to extra nuclear lysosomes. Pharmacologic inhibition of the above AKRs in doxorubicin-resistant cells increased cellular doxorubicin levels, restored doxorubicin cytotoxicity and re-established doxorubicin localization to the nucleus. The properties of doxorubicinol were unaffected.ConclusionsThese findings demonstrate the utility of using curated pharmacokinetic and pharmacodynamic knowledge bases to identify highly relevant genes associated with doxorubicin resistance. The induction of one or more of these genes was found to be correlated with changes in the drug’s properties, while inhibiting one specific class of these genes (the AKRs) increased cellular doxorubicin content and restored drug DNA binding, cytotoxicity, and subcellular localization.

Genome-wide identification of structural variants in genes encoding drug targets

The objective of the present study was to identify structural variants of drug target-encoding genes on a genome-wide scale. We also aimed at identifying drugs that are potentially amenable for individualization of treatments based on knowledge about structural variation in the genes encoding their targets. Information about human drug targets of all therapeutic drugs and nutraceuticals approved by the Food and Drug Administration and with an Anatomical Therapeutic Chemical (ATC) code, namely, 876, was obtained from the DrugBank and applied to interrogate the Database of Genomic Variants. We identified 1721 structural variants, which affected 495 of 1005 different genes encoding drug targets. About 70% of the Food and Drug Administration-approved drugs had targets subjected to structural variation, in particular copy number variation. The distribution of drugs with targets encoded by copy number variable genes differed between ATC groups with pronounced over-representation in ATC group N, that is, nervous system drugs (P=3.75e-5). Several narrow therapeutic index drugs with targets subjected to genomic structural variation were identified. Information about the frequencies of the structural variants and drug consumption allowed us to identify potential candidates for implementation in pharmacogenetic testing and individualized drug treatments. Structural variants in pharmacodynamic genes may play a larger role in determining individual variation in drug responses than currently believed. Inclusion of such genes in pharmacogenetic testing holds promising prospects as they may have large effect sizes.

Biomarkers to optimize the treatment of nicotine dependence.

The application of genomic medicine to the treatment of nicotine dependence holds great promise for revitalizing the steady decline in smoking rates witnessed in the USA over the past several decades. This paper examines the current knowledge base concerning the use of biomarkers to guide the selection of nicotine dependence treatments. First, we review the neurobiology of nicotine dependence and present evidence that supports its heritability. We then discuss the various studies of pharmacokinetic and pharmacodynamic genes related to therapeutic response. Current evidence suggests that biomarkers of genetic variability in both nicotine metabolism, referred to as the nicotine metabolite ratio, and dopamine genotypes may be useful for guiding treatment selection for nicotine dependence. Barriers to the translation of this research to clinical practice are discussed, as are directions for future research.

Pharmacogenomics genes show varying perceptibility to microRNA regulation

The aim of pharmacogenomics is to identify individual differences in genome and transcriptome composition and their effect on drug efficacy. MicroRNAs (miRNAs) are short noncoding RNAs that negatively regulate expression of the majority of animal genes, including many genes involved in drug efficacy. Consequently, differences in the miRNA expression among individuals could be an important factor contributing to differential drug response. Pharmacogenomics genes can be divided into drug target genes termed as pharmacodynamics genes (PD) and genes involved in drug transport and metabolism termed as pharmacokinetics genes (PK). To clarify the regulatory potential of miRNAs in pharmacogenomics, we have examined the potential regulation by miRNAs of PK and PD genes. We identified PK and PD genes as annotated by the Pharmacogenomics Knowledge Base and examined miRNA targeting of genes in the two groups according to several miRNA target prediction databases. We furthermore studied how differences between the two groups are reflected in the gene structure and across gene families. Lastly, we studied changes in expression levels of PK versus PD genes in cells depleted for miRNAs by shRNA-mediated knockdown of the miRNA-processing enzyme Dicer. Our analysis identify a striking difference in the level of miRNA regulation between PK and PD genes, with the former having less than half predicted conserved miRNA binding sites compared with the latter. Importantly, this finding is reflected in a highly significant difference in the shift in expression levels of PD versus PK genes after depletion of miRNAs. Our study emphasizes an intrinsic difference between PK and PD genes and helps clarify the role of miRNAs in pharmacogenomics.

Abstract 2230: Quantitative expression of the hedgehog (Hh) signaling pathway in gastric carcinoma: A novel protocol to process RNA from paraffin-embedded tissue

Abstract Background: The Hh pathway is an evolutionally highly conserved signaling cascade important in gastroesophageal embryonic pattern formation and stem cell response to tissue damage. Its aberrant activation has also been implicated in gastric cancer formation and progression. Multiple therapeutics targeting the Hh pathway have been developed and in order to test their activity and pharmacodynamic responses, routine and consistent gene expression measurement from clinical samples must be available. Aims and Methods: The aim of this work was to measure levels of Hh pathway expression in both gastric tumors and normal gastric tissue, using a novel protocol of processing RNA from formalin fixed, paraffin-embedded tissue (FFPET). Total RNA was extracted from FFPET using a combination of Qiagen and RecoverAllTM kits according to the manufacturer's protocol(s). cDNA was synthesized using the iScriptTMcDNA Synthesis Kit and then a minimum of 20 ng RNA was pre-amplified using an Applied Biosystems pre-amplification cDNA kit. The primers for the Shh and Gli1genes were then added to the pre-amplification reaction and TaqManPreAmp master mix, amplified for 14 cycles on a thermal cycler and then real time PCR carried out for 40 cycles in duplicate. The relative quantification of the Shh and Gli1 genes were compared to the reference gene succinate dehydrogenase complex subunit A (SDHA) where the ratio for the change in expression for the selected gene = 2−ΔΔCT. Results: The levels of gene expression in gastric adenocarcinomas for Shh and Gli1 were respectively 3.89 ± 0.49 (mean ± SEM, N = 11) and 4.57 ± 1.46. For 8 non-tumor gastric specimens, the CT values for Shh ranged from 30.24 to 35.81 and for Gli1 from 31.21 to 34.81 while for SDHA the mean CT was 18.4 ± 1.87. Based on these CT values, no expression of Shh and Gli1 was present in these non-tumor gastric tissues. Conclusion: Hh pathway signaling can be quantitatively measured using as little as 20ng of RNA obtained from FFPET, making this methodology valuable in the clinic where tissue acquisition is often limited, as for gastric tumors. Using our methodology we found that there is increased Hh pathway expression in gastric carcinomas as compared to normal tissue, a finding consistent with previous reports in the literature. Supported by NO1-CM-07103-74 RECOVERY – ACTNOW Clinical Trial 8376 and NCI 2P30 CA16087-23, Tissue Acquisition and Banking Core. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2230. doi:10.1158/1538-7445.AM2011-2230

Pharmacogenetics of antidepressant response.

Personalized medicine - the adaptation of therapies based on an individual's genetic and molecular profile - is one of the most promising aspects of modern medicine. The identification of the relation between genotype and drug response, including both the therapeutic effect and side effect profile, is expected to deeply affect medical practice. In this paper, we review the current knowledge about the genes related to antidepressant treatment response and provide methodologic proposals for future studies. We have mainly focused on genes associated with pharmacodynamics, for which a list of promising genes has been identified despite some inconsistency across studies. We have also synthesized the main results for pharmacokinetic genes, although so far they seem less relevant than those for pharmaco dynamic genes. We discuss possible reasons for these inconsistent findings and propose new study designs.

Compilation of a Comprehensive Gene Panel for Systematic Assessment of Genes that Govern an Individual’s Drug Responses

Polymorphisms of genes involved in the pharmacokinetic and pharmacodynamic processes underlie the divergent drug responses among individuals. Despite some successes in identifying these polymorphisms, the candidate gene approach suffers from insufficient gene coverage whereas the genome-wide association approach is limited by less than ideal coverage of SNPs in some important genes. To expand the potential of the candidate approach, we aim to delineate a comprehensive network of drug-response genes for in-depth genetic studies. Pharmacologically important genes were extracted from various sources including literatures and web resources. These genes, along with their homologs and regulatory miRNAs, were organized based on their pharmacological functions and weighted by literature evidence and confidence levels. Their coverage was evaluated by analyzing three commercial SNP chips commonly used for genome-wide association studies: Affymetrix SNP array 6.0, Illumina HumanHap1M and Illumina Omni. A panel of drug-response genes was constructed, which contains 923 pharmacokinetic genes, 703 pharmacodynamic genes and 720 miRNAs. There are only 16.7% of these genes whose all known SNPs can be directly or indirectly (r(2) > 0.8) captured by the SNP chips with coverage of more than 80%. This is possibly because these SNPs chips have notably poor performance over rare SNPs and miRNA genes. We have compiled a panel of candidate genes that may be pharmacologically important. Using this knowledgebase, we are able to systematically evaluate genes and their variants that govern an individual's response to a given pharmaceutical therapy. This approach can serve as a necessary complement to genome-wide associations.

Irinotecan Pharmacogenomics

Irinotecan is a camptothecin analog used as an anticancer drug. Severe, potentially life-threatening toxicities can occur from irinotecan treatment. Although multiple genes may play a role in irinotecan activity, the majority of evidence to date suggests that variation in expression of UGT1A1 caused by a common promoter polymorphism (UGT1A1*28) is strongly associated with toxicity; however, this link is dose dependent. Variations in other pharmacokinetic genes, particularly the transporter ABCC2, also contribute to irinotecan toxicity. In addition, recent studies have shown that pharmacodynamic genes such as TDP1 and XRCC1 can also play a role in both toxicity and response.

Pharmacodynamic Genes do not Influence Risk of Neutropenia in Cancer Patients Treated with Moderately High-Dose Irinotecan

A recent study found that variation in camptothecin pharmacodynamic genes (TOP1, PARP1, TDP1 and XRCC1) correlated with efficacy and risk of neutropenia in irinotecan-treated cancer patients (median dose: 180 mg/m2), which suggests that these genes might predict outcomes to irinotecan-based therapies. The present study was conducted to evaluate previous gene associations using an independent sample of patients receiving irinotecan. DNA was isolated from 85 advanced cancer patients treated with 300 or 350 mg/m2 irinotecan and genotyped for haplotype-tag polymorphisms across TOP1, PARP1, TDP1 and XRCC1. Associations between genotypes and haplotypes and log(absolute neutrophil count nadirs) were assessed by linear regression. No associations were observed. Our findings suggest that the genes we tested do not influence toxicity of irinotecan when adminstered at 300-350 mg/m2.

Pharmacodynamic genes do not influence risk of neutropenia in cancer patients treated with moderately high-dose irinotecan

Pharmacodynamic genes do not influence risk of neutropenia in cancer patients treated with moderately high-dose irinotecan

Irinotecan Pharmacogenetics: Influence of Pharmacodynamic Genes

Irinotecan is an important drug for the treatment of solid tumors. Although genes involved in irinotecan pharmacokinetics have been shown to influence toxicity, there are no data on pharmacodynamic genes. CDC45L, NFKB1, PARP1, TDP1, and XRCC1 have been shown to influence the cytotoxic action of camptothecins, including irinotecan. Polymorphisms in the drug target of camptothecins, topoisomerase I (TOP1), and downstream effectors may influence patient outcomes to irinotecan therapy. We undertook a retrospective candidate gene haplotype association study to investigate this hypothesis. Haplotype compositions of six candidate genes were constructed in European (n = 93), East Asian (n = 94), and West African (n = 95) populations. Haplotype-tagging single nucleotide polymorphisms (htSNP) were selected based on genealogic relationships between haplotypes. DNA samples from 107 European, advanced colorectal cancer patients treated with irinotecan-based regimens were genotyped for htSNPs as well as three coding region SNPs. Associations between genetic variants and toxicity (grade 3/4 diarrhea and neutropenia) or efficacy (objective response) were assessed. TOP1 and TDP1 htSNPs were related to grade 3/4 neutropenia (P = 0.04) and response (P = 0.04), respectively. Patients homozygous for an XRCC1 haplotype (GGCC-G) were more likely to show an objective response to therapy than other patients (83% versus 30%; P = 0.02). This effect was also seen in a multivariate analysis (odds ratio, 11.9; P = 0.04). No genetic variants were associated with diarrhea. This is the first comprehensive pharmacogenetic investigation of irinotecan pharmacodynamic factors, and our findings suggest that genetic variation in the pharmacodynamic genes may influence the efficacy of irinotecan-containing therapies in advanced colorectal cancer patients.

Clinical Guidelines for Psychiatrists for the Use of Pharmacogenetic Testing for CYP450 2D6 and CYP450 2C19

Pharmacogenetics has arrived in clinical psychiatric practice with the FDA approval of the AmpliChip CYP450 Test that genotypes for two cytochrome P450 2D6 (CYP2D6) and 2C19 (CYP2C19) genes. Other pharmacogenetic tests, including those focused on pharmacodynamic genes, are far from ready for clinical application. CYP2D6 is important for the metabolism of many antidepressants and antipsychotics, and CY2C19 is important for some antidepressant metabolism. Poor metabolizers (PMs), lacking the enzyme, account for up to 7% of Caucasians for CYP2D6 and up to 25% of East Asians for CYP2C19. Patients having three or more active CYP2D6 alleles (up to 29% in North Africa and the Middle East), are called CYP2D6 ultra-rapid metabolizers (UMs). CYP2D6 phenotypes (particularly PMs) are probably important in patients taking tricyclic antidepressants (TCAs), venlafaxine, typical antipsychotics, and risperidone. The CYP2C19 PM phenotype is probably important in patients taking TCAs and perhaps citalopram, escitalopram, and sertraline. On the basis of the literature and the authors' clinical experience, the authors provide provisional recommendations for identifying and treating CYP2D6 PMs, CYP2C19 PMs, and CYP2D6 UMs. The next few years will determine whether CYP2D6 genotyping is beneficial for patients taking the new drugs aripiprazole, duloxetine, and atomoxetine. Practical recommendations for dealing with laboratories offering CYP2D6 and CYP2C29 genotyping are provided.

Tipifarnib (ZARNESTRATM in Previously Untreated Poor-Risk AML of the Elderly: Updated Results of a Multicenter Phase 2 Trial.

Farnesyltransferase inhibitors (FTI) make up a novel class of anti-cancer agents that competitively and selectively inhibit farnesyl protein transferase. Early trials of the orally bioavailable non-peptidomimetic FTI tipifarnib (ZARNESTRATM, Johnson & Johnson PRD) demonstrated both clinical responses and excellent tolerability in patients with poor-risk or refractory acute myeloid leukemia (AML). (Karp, et al. Blood 97:3361, 2001). We herein report updated results of a multicenter phase 2 trial of tipifarnib in an elderly, previously untreated poor-risk AML population who refused or were deemed unfit for conventional induction chemotherapy. Tipifarnib was administered orally in the outpatient setting at a dose of 600 mg BID for 21 days, followed by a 1–3 week recovery period. Up to 4 cycles of tipifarnib were permitted in patients with complete responses (CR). The primary endpoint was overall response rate (CR + PR). Secondary endpoints included toxicity rates, measurement of markers of farnesylation (HDJ-2) in bone marrow cells, measurement of signaling intermediates ERK and AKT, and RNA microarray expression patterns. Accrual to the trial is complete. 170 patients have been enrolled, 148 of whom are evaluable for response (AML=160; high-risk MDS=4; high-risk CMML=6). The median age was 73 years (range 34–85), and 76 patients (45%) were age = 75. M/F ratio was 2:1. An unfavorable karyotype and/or antecedent MDS was present in 47% and 79% of patients, respectively. The median number of cycles received was 1, and the median number of days of drug received was 36 days. Dose reductions were implemented in 38% of patients, more commonly in cycles subsequent to cycle #1. The overall response rate (CR + PR) was 34%. CR occurred in 18% of patients. Responses were evenly distributed across study centers. In patients ≥ 75 years, the overall response rate was 30% (CR 20 %). Median CR duration was 6.4 months (range 1.5–11+ months). Median overall survival was 5.6 months for all patients. CR patients had a median survival of 14.4 months, with 63% alive at 12 months. In non-responders, median survival was 3.1 months. The incidence of grade = 3 tipifarnib-related non-hematologic adverse events was 43%, comprised mainly of infectious and gastrointestinal complications. The hospitalization rate for tipifarnib-related toxicity was 18% (median duration: 12 days). The death rate from tipifarnib-related toxicity at 6 weeks was 5%. Microarray analysis of pre-and post-treatment bone marrow samples is being performed to identify both predictive and pharmacodynamic gene markers of response to tipifarnib. In summary, tipifarnib is a novel outpatient treatment with activity in previously untreated poor-risk AML. The low hospitalization rate may reflect the low incidence of severe non-hematological toxicity.

Association of pharmacokinetic (CYP2C9) and pharmacodynamic (factors II, VII, IX,andX;proteins SandC; and γ-glutamyl carboxylase) gene variants with warfarin sensitivity

AbstractWe analyzed mutations of 7 vitamin K—dependent protein and cytochrome P450 2C9 genes in 45 patients and investigated whether any contribute to the large interpatient variability in the warfarin dose-effect relationship. Total clearance and daily dose, INR and INR/Cp, were used as pharmacokinetic and pharmacodynamic indexes, respectively. Patients were grouped by genotype based on a single polymorphism and combinations of polymorphisms. Among the 30 sequence variants identified,CYP2C9*3, 165Thr → Metof thefactor IIgene, -402G → A, (37-bp repeat)n, and -746T → Cof thefactor VIIgene, and(CAA repeat)nof the γ-glutamyl carboxylasegene were selected as candidate polymorphisms. As the analysis of single polymorphisms implied, the highest INR/Cp mean values and the lowest warfarin maintenance doses were observed in patients homozygous for the165Met, -402G, (37-bp repeat)6and -746Talleles. Multiple regression analysis revealed that warfarin sensitivity was independently associated with -402G→A, (CAA repeat)n,CYP2C9*3, and165Thr → Met, which accounted for 50% of variance. These results suggest that part of the considerable interpatient variation is attributable to genetic variation, and the combined genotyping ofCYP2C9and certain vitamin K—dependent protein genes is useful for predicting anticoagulant responses.