Differential effects of 2C9*3 and 2C9*2 variants of cytochrome P-450 CYP2C9 on sensitivity to acenocoumarol

Genome-Wide Association Study of VKORC1 and CYP2C9 on acenocoumarol dose, stroke recurrence and intracranial haemorrhage in Spain

Acenocoumarol is an oral anticoagulant with significant interindividual dose variations. Variants in CYP2C9 and VKORC1 have been associated with acenocoumarol maintenance dose. We analysed whether any of the 49 polymorphisms in CYP2C9 and VKORC1 previously associated with acenocoumarol maintenance dose in a Genome-Wide Association study (GWAs) in Dutch population are associated with stroke recurrence, intracranial haemorrhage (ICH) and acenocoumarol maintenance dose in a Spanish population. We performed a GWAs using Human Core Exome-chip (Illumina) in 78 patients stroke patients treated with acenocoumarol for secondary prevention enrolled as part of the prospective investigator-initiated study (IIS) SEDMAN Study. Patients were followed-up a median of 12.8 months. Three and eight patients had recurrent stroke and ICH events, respectively. We found 14 of the 49 published variants associated with acenocoumarol maintenance dose (p < 0.05). Six polymorphisms were associated with stroke recurrence and four variants with ICH (p < 0.05). In conclusion, variants in VKORC1 and CYP2C9 are associated with acenocoumarol maintenance dose, stroke recurrence and ICH in a Spanish cohort. These results highlight the relevance of studying pharmacogenetics associated with efficacy and safety of anticoagulant drugs and justify studies with larger sample size and different ethnic populations.

Oral Anticoagulant Therapy-When Art Meets Science

Anticoagulant treatment is extremely important and frequently encountered in the therapy of various cardiovascular diseases. Vitamin K antagonists (VKA) are in use for the prevention and treatment of arterial and venous thromboembolism, despite the introduction of new direct-acting oral anticoagulants (NOAC). The VKA still have the clear recommendation in patients with a mechanical prosthetic heart valve replacement or moderate to severe mitral stenosis of the rheumatic origin, in deep vein thrombosis associated with congenital thrombophilia, and in cases where NOAC are prohibited by social condition (financial reason) or by comorbidities (extreme weight, severe renal or liver disease). VKA dosing required to reach the targeted therapeutic range varies largely between patients (inter-individual variability). This inter-individual variability depends on multiple environmental factors such as age, mass, diet, etc. but it is also influenced by genetic determinism. About 30 genes implicated in the metabolism coumarins derivatives were identified, the most important being CYP2C9 and VKORC, each with several polymorphisms. Herein, we review the data regarding genetic alterations in general and specific populations, highlight the diagnosis options in particular cases presenting with genetic alteration causing higher sensitivity and/or resistance to VKA therapy and underline the utility of NOAC in solving such rare and difficult problems.

Extremely low therapeutic doses of acenocoumarol in a patient with CYP2C9*3/*3 and VKORC1-1639A/A genotype

Vitamin-K antagonists (VKAs) have remained the mainstay of oral anticoagulant therapy for the treatment and prevention of thromboembolism. The management of treatment with VKAs is challenging due to their narrow therapeutic index and the wide interindividual variation in response to therapy. Variants of the CYP2C9 and the VKORC1 gene account for 30–50% of the variability in dosing requirements, and it has been proposed that genotyping of these loci could facilitate management of VKA therapy and minimize risk of overanticoagulation, even in very low doses. We present the first reported case of a patient with the compounded genotype CYP2C9*3*3 and VKORC1-1639A/A under treatment with acenocoumarol, and review of other reported cases with analogous genotypic profiles but under treatment with warfarin.

Effects of CYP2C11 gene knockout on the pharmacokinetics and pharmacodynamics of warfarin in rats

1. CYP2C11 is the most abundant isoform of cytochrome P450s (CYPs) in male rats and is considered the main enzyme for warfarin metabolism. 2. To further access the in vivo function of CYP2C11 in warfarin metabolism and efficacy, a CYP2C11-null rat model was used to study warfarin metabolism with both in vitro and in vivo approaches. Prothrombin time (PT) of warfarin was also determined. 3. The maximum rate of metabolism (V_max) and intrinsic clearance (CL_int) of liver microsomes from CYP2C11-null males were reduced by 37 and 64%, respectively, compared to those in Sprague Dawley (S-D) rats. The K_m of liver microsomes from CYP2C11-null males was increased by 73% compared to that of S-D rats. The time to reach the maximum plasma concentration (T_max) of warfarin in CYP2C11-null males was significantly delayed compared to that in S-D males, and the CL rate was also reduced. The PT of CYP2C11-null rats was moderately longer than that of S-D rats. 4. In conclusion, the clearance rate of warfarin was mildly decreased and its anticoagulant effect was moderately increased in male rats following CYP2C11 gene knockout. CYP2C11 played a certain role in the clearance and efficacy of warfarin, while it did not seem to be essential.

Pharmacogenetics of vitamin K antagonists and bleeding risk prediction in atrial fibrillation

BACKGROUND

Polymorphisms in the vitamin K epoxide reductase complex 1 (VKORC1) and cytochrome P450 2C9 (CYP2C9) genes increase the bleeding risk in anticoagulated atrial fibrillation (AF) patients. Here, we aimed to investigate whether VKORC1 and CYP2C9 polymorphisms improved the predictive performance for major bleeding using the HAS-BLED score.

MATERIAL AND METHODS

We recruited 652 consecutive AF patients stable on vitamin K antagonist (INR 2.0-3.0) during at least the previous 6 months. A baseline venous blood sample was obtained for DNA extraction. We gave an extra point to the HAS-BLED score if the patient was a simultaneous carrier of the VKORC1 and CYP2C9 polymorphisms related to bleeding, and we called this modified score "GEN|HAS-BLED." During a median follow-up of 7.6 years (IQR 5.6-8.0), all major bleeding events were recorded.

RESULTS

During follow-up, 106 (16.2%) patients experienced a major bleeding (2.81%/y; 42 intracranial haemorrhages and 44 gastrointestinal bleeding) and 24 (3.7%) died from major bleeding (0.48%/y). Cox regression analyses demonstrated a significant association between HAS-BLED or GEN|HAS-BLED and major bleeds, both as continuous or categorical scores. Comparison of receiver operating characteristic (ROC) curves shows that original HAS-BLED clinical score had better predictive ability than GEN|HAS-BLED (0.660, 95% CI 0.622-0.696 vs 0.645, 95% CI 0.607-0.682; P = .030). Discrimination and reclassification analyses showed that GEN|HAS-BLED did not improve sensitivity compared with the original score and even showed significant negative reclassification.

CONCLUSION

Adding pharmacogenetic factors (ie polymorphisms of the VKORC1 and CYP2C9 genes) to the HAS-BLED score does not improve the prediction or discrimination performance for major bleeding.

Creating a genotype-based dosing algorithm for acenocoumarol steady dose

Acenocoumarol is a commonly prescribed anticoagulant drug for the prophylaxis and treatment of venous and arterial thromboembolic disorders in several countries. In counterpart of warfarin, there is scarce information about pharmacogenetic algorithms for steady acenocoumarol dose estimation. The aim of this study was to develop an algorithm of prediction for acenocoumarol.The algorithm was created using the data from 973 retrospectively selected anticoagulated patients and was validated in a second independent cohort adding up to 2,683 patients. The best regression model to predict stable dosage in the Primary Cohort included clinical factors (age and body mass index, BSA) and genetic variants (VKORC1, CYP2C9* and CYP4F2 polymorphisms) and explained up to 50% of stable dose. In the validation study the clinical algorithm yielded an adjusted R2=0.15 (estimation´s standard error=4.5) and the genetic approach improved the dose forecast up to 30% (estimation´s standard error=4.6). Again, the best model combined clinical and genetic factors (R2= 0.48; estimation´s standard error=4) which provided the best results of doses estimates within 20% of the real dose in patients taking lower (≤7mg/week) or higher (≥25mg/week) acenocoumarol doses. In conclusion, we developed a prediction algorithm using clinical data and three polymorphisms in VKORC1, CYP2C9* and CYP4F2 genes that provided a steady acenocoumarol dose for about 50% of patients in the Validation Cohort. Such algorithm was especially useful to patients who need higher or lower acenocoumarol doses, those patients with higher time required until their stabilisation and are more prone to suffer a treatment derived complication.

Genotyping of CYP2C9 and VKORC1 polymorphisms predicts south Indian patients with deep vein thrombosis as fast metabolizers of warfarin/acenocoumarin

Deep vein thrombosis (DVT) is a life-threatening disease. Warfarin and acenocoumarol are anticoagulants used to treat DVT and vary among individuals in terms of treatment response/toxicity. Single nucleotide polymorphisms (SNPs) in CYP2C9 and VKORC1 play a role in the pharmacokinetics and dynamics of warfarin and acenocoumarol and they determine the efficacy of treatment by controlling drug clearance in treated individuals. The aim of the current study was to genotype the critical SNPs of CYP2C9 and VKORC1 genes in a south Indian population in order to understand the metabolizer phenotype of patients with DVT. CYP2C9 (rs1799853, rs1057910, rs1057909, rs28371686) and VKORC1 (rs9923231) SNPs were genotyped in 124 cases of DVT. Genomic regions of these SNPs from genomic DNA were amplified with PCR and directly sequenced using Sanger sequencing except for the SNP rs1799853, which was detected using Sau96I restriction endonuclease-based digestion of variant alleles. Among south Indian patients with DVT, 6.5% (8/124) had the rs1799853 SNP of CYP2C9 and 11% (14/124) had the rs1057910 SNP while 16% (20/124) had the rs9923231 SNP of VKORC1 which were associated with the response to warfarin treatment. None of the patients tested positive for poor drug metabolizing genotypes of the CYP2C9 gene and only 1.6% of the south Indian population was sensitive to warfarin treatment. Genotyping results suggest that a relatively greater amount of the therapeutic drug is required to achieve/maintain the international normalized ratio (INR) in south Indian patients with DVT.

Influence of VKORC1 and CYP2C9 Polymorphisms on Daily Acenocoumarol Dose Requirement in South Indian Patients With Mechanical Heart Valves

Background and Aim:

Chronic rheumatic heart disease (RHD) patients who undergo valve replacement with mechanical valves require lifelong anticoagulation. Acenocoumarol, a vitamin K antagonist has a narrow therapeutic range and wide inter-individual variability. Our aim was to investigate the influence of polymorphisms of VKORC1 and CYP2C9 genes on the mean daily dose requirement of acenocoumarol.

Methods:

205 chronic RHD patients, with mechanical heart valves and on acenocoumarol therapy, were recruited. Genotyping for VKORC1 (−1639G>A and 1173C>T) and CYP2C9 (*2 & *3 alleles) polymorphisms was done by PCR-RFLP. There was complete linkage disequilibrium between VKORC1 polymorphisms (r2 = 0.98, D′ = 1.0, LOD = 74.02). VKORC1 genotype distribution for GG/CC, GA/CT, and AA/TT were 57.6%, 36.1%, and 6.3%, respectively. CYP2C9 genotype distribution for *1/*1, *1/*3, *1/*2, *2/*2, and *2/*3 were 78.5%, 14.1%, 6.3%, 0.5%, and 0.5%, respectively. Patients with a wild type of both VKORC1 (−1639GG and 1173CC) and CYP2C9 gene variants required higher acenocoumarol dose compared to those with mutant genotype ( P = 0.023 and P = 0.008 respectively). On combined genotype analysis, patients having a combination of wild type of VKORC1 with wild type of CYP2C9 (44.4%) required higher daily dose compared to patients bearing heterozygous VKORC1 (−1639GA & 1173CT) with wild type of CYP2C9 (30.2%, P = 0.008).

Conclusion:

Presence of a mutant allele of VKORC1 (−1639A & 1173T) and CYP2C9 genes increased the odds of requiring a lower mean dosage of acenocoumarol. Studying the combination of genotypes in RHD patients could predict acenocoumarol dose requirement more accurately.

High prevalence of VKORC1*3 (G9041A) genetic polymorphism in north Indians: A study on patients with cardiac disorders on acenocoumarol

Coumarin derivatives such as warfarin and acenocoumarol are used in various disorders such as deep venous thrombosis, pulmonary embolism, atrial fibrillation and artificial heart valves. They have improved prognosis of patients with thromboembolic disease. An individual's response to coumarins depends on several factors. The non-genetic factors include age, gender, body mass index, diet and interacting drugs. Among the genetic factors, the cytochrome P450 system and vitamin K epoxide reductase complex subunit 1 play a key role in drug metabolism. This was a prospective hospital based study in which allele and genotypic frequencies of CYP2C9 gene polymorphisms; 430C>T and 1075A>C and VKORC1 gene polymorphisms; 1639G>A, 9041G>A and 6009C>T in 106 alleles of north Indian patients with valve replacement on acenocoumarol were determined and their effect on acenocoumarol dosing was studied. To the best of our knowledge, this is first report of VKORC1 9041G>A and 6009C>T gene polymorphisms and their effect on acenocoumarol dosing from north India. In 53 patients with valve replacement on acenocoumarol with stable INR, the allele frequency of CYP2C9*2 and CYP2C9*3 gene polymorphisms was 0.05 and 0.17 respectively and that of VKORC1 *2,*3 and *4 gene polymorphisms was 0.15, 0.72 and 0.11 respectively. The presence of CYP2C9*3 or VKORC1*2 gene polymorphism were associated with decrease in acenocoumarol dose requirements (p values 0.03 and 0.02 respectively).This study confirmed the association of lower mean weekly dosages of acenocoumarol in patients with CYP2C9*3 and VKORC1*2 gene polymorphisms. An unusually high frequency of 9041A polymorphism in VKORC1 was found in study population.

Role of CYP2C9, VKORC1 and Calumenin Genotypes in Monitoring Warfarin Therapy: An Egyptian Study

Background: Oral anticoagulant therapy is conditioned by environmental and genetic factors.Objectives: To verify the effect of the calumenin, cytochrome P-450 variants and VKORC1 genetic polymorphisms on the response to warfarin therapy and warfarin dose adjustment.Patients and Methods: We selected fifty warfarin treated patients with dose adjusted at INR value between 2 and 3. PCR-RFLP is used for of calumenin gene polymorphism. Insitu Hybridization was used for identification of VKORC1 promoter and CYP2C9 variants polymorphisms.Results: The warfarin dose in the patients with Calumenin and CYP2C9 genetic polymorphism was lower than the wild type gene. The warfarin dose in the patients with VKORC1 variants was statistically lower compared to that of the wild-type. The presence of combined CYP2C9 genetic variants and VKORC1 polymorphism was associated with lower warfarin dose than that the wild types.Conclusion: Calumenin (CALU) might be a new genetic factor involved in the pharmacogenetics of anticoagulant therapy.

Comparative genetics of warfarin resistance

Warfarin and other 4-hydroxycoumarin-based oral anticoagulants targeting vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) are administered to humans, mice and rats with different purposes in mind - to act as pesticides in high-dosage baits for killing rodents, but also to save lives when administered in low dosages as antithrombotic drugs in humans. However, high-dosage warfarin used to control rodent populations has resulted in numerous mutations causing warfarin resistance. Currently, six single missense mutations in mice, 12 distinct missense mutations in rats, as well as compound heterozygous or homozygous mutations with up to six distinct missense mutations per Vkorc1 allele have been described. Warfarin resistance missense mutations for human VKORC1 have also been found world-wide, but differ characteristically from those in rodents. In humans, 26 distinct mutations have been characterized, but occur only rarely either in heterozygous or, even rarer, in homozygous form. In this review, we summarize the known VKORC1 missense mutations causing warfarin and other 4-hydroxycoumarin drug resistance, identify genomics databases as new sources of data, explore possible underlying genetic mechanisms, and summarize similarities and differences between warfarin resistant VKORC1 variants in humans and rodents.

Association of polymorphism in cytochrome P450 2C9 with susceptibility to head and neck cancer and treatment outcome

The present case–control study involving 750 cases and equal number of healthy controls investigates the association of polymorphism in cytochrome P450 2C9 (CYP2C9) with head and neck squamous cell carcinoma (HNSCC) and response in patients receiving chemotherapy or combination of radio-chemotherapy. The frequency of heterozygous or homozygous genotypes of CYP2C9*2 & CYP2C9*3, which leads to the poor metabolizer (PM) genotype was significantly higher in HNSCC cases when compared to the healthy controls resulting in significantly increased risk in the cases. Tobacco use in the form of tobacco smoking or tobacco chewing was found to increase the risk several fold in cases when compared to the non-tobacco users. Likewise, alcohol intake in cases with variant genotypes of CYP2C9*2 or CYP2C9*3 also significantly increased the HNSCC risk in cases when compared to non-alcohol users. Further, majority of the cases carrying variant alleles of both CYP2C9*2 or CYP2C9*3 were found to respond poorly to the chemotherapy or combination of radio-chemotherapy. The data suggests a significant association of the CYP2C9 polymorphism with HNSCC and treatment outcome.

Applications of CYP450 testing in the clinical setting

Interindividual variability in drug response is a major clinical problem. Polymedication and genetic polymorphisms modulating drug-metabolising enzyme activities (cytochromes P450, CYP) are identified sources of variability in drug responses. We present here the relevant data on the clinical impact of the major CYP polymorphisms (CYP2D6, CYP2C19 and CYP2C9) on drug therapy where genotyping and phenotyping may be considered, and the guidelines developed when available. CYP2D6 is responsible for the oxidative metabolism of up to 25% of commonly prescribed drugs such as antidepressants, antipsychotics, opioids, antiarrythmics and tamoxifen. The ultrarapid metaboliser (UM) phenotype is recognised as a cause of therapeutic inefficacy of antidepressant, whereas an increased risk of toxicity has been reported in poor metabolisers (PMs) with several psychotropics (desipramine, venlafaxine, amitriptyline, haloperidol). CYP2D6 polymorphism influences the analgesic response to prodrug opioids (codeine, tramadol and oxycodone). In PMs for CYP2D6, reduced analgesic effects have been observed, whereas in UMs cases of life-threatening toxicity have been reported with tramadol and codeine. CYP2D6 PM phenotype has been associated with an increased risk of toxicity of metoprolol, timolol, carvedilol and propafenone. Although conflicting results have been reported regarding the association between CYP2D6 genotype and tamoxifen effects, CYP2D6 genotyping may be useful in selecting adjuvant hormonal therapy in postmenopausal women. CYP2C19 is responsible for metabolising clopidogrel, proton pump inhibitors (PPIs) and some antidepressants. Carriers of CYP2C19 variant alleles exhibit a reduced capacity to produce the active metabolite of clopidogrel, and are at increased risk of adverse cardiovascular events. For PPIs, it has been shown that the mean intragastric pH values and the Helicobacter pylori eradication rates were higher in carriers of CYP2C19 variant alleles. CYP2C19 is involved in the metabolism of several antidepressants. As a result of an increased risk of adverse effects in CYP2C19 PMs, dose reductions are recommended for some agents (imipramine, sertraline). CYP2C9 is responsible for metabolising vitamin K antagonists (VKAs), non-steroidal anti-inflammatory drugs (NSAIDs), sulfonylureas, angiotensin II receptor antagonists and phenytoin. For VKAs, CYP2C9 polymorphism has been associated with lower doses, longer time to reach treatment stability and higher frequencies of supratherapeutic international normalised ratios (INRs). Prescribing algorithms are available in order to adapt dosing to genotype. Although the existing data are controversial, some studies have suggested an increased risk of NSAID-associated gastrointestinal bleeding in carriers of CYP2C9 variant alleles. A relationship between CYP2C9 polymorphisms and the pharmacokinetics of sulfonylureas and angiotensin II receptor antagonists has also been observed. The clinical impact in terms of hypoglycaemia and blood pressure was, however, modest. Finally, homozygous and heterozygous carriers of CYP2C9 variant alleles require lower doses of phenytoin to reach therapeutic plasma concentrations, and are at increased risk of toxicity. New diagnostic techniques made safer and easier should allow quicker diagnosis of metabolic variations. Genotyping and phenotyping may therefore be considered where dosing guidelines according to CYP genotype have been published, and help identify the right molecule for the right patient.

Effect of different genetics variants: CYP2C9*2, CYP2C9*3 of cytochrome P-450 CYP2C9 and 1639G>A of the VKORC1 gene; On acenocoumarol requirement in Moroccan patients

Coumarin derivatives such as acenocoumarol represent the therapy of choice for the long-term treatment and prevention of thromboembolic diseases. Many genetics determinants involved in the metabolism of acenocoumarol have been shown to influence the anticoagulant dosage. The aim of this work was to evaluate, for the first time in Maghreb, the allelic frequencies of CYP2C9*2, CYP2C9*3 and VKORC1 -1639G>A mutations, and to establish the role of this polymorphisms in modulating the acenocoumarol requirement in Moroccan patients receiving anticoagulation treatment. Three groups of patients, with low, medium, or high acenocoumarol dose requirements were studied. Genetic analyses of VKORC1 -1639G>A, CYP2C9*2, and CYP2C9*3, were performed in 114 Moroccan patients with stable acenocoumarol dose. The results showed that the allelic frequencies of the three mutations studied was varies, most of patients having CYP2C9*2 and CYP2C9*3 mutations belong to a group with low dose of acenocoumarol, with P-value of 0.0082 and the single patient with CYP2C9*3 on homozygous form belongs to the same group and carried the A allele for VKORC1 gene. In conclusion, the present study confirmed the large interindividual variability in acenocoumarol maintenance dose due to CYP2C9*2, CYP2C9*3 and VKORC1 -1639G>A polymorphisms, and demonstrated that these alleles modulates sensitivity to acenocoumarol, a finding indicating that a reduced initial loading dose of acenocoumarol should be used in carriers of this allele, also, she indicates the usefulness of predictive testing concerning these mutations when an hypocoagulability is installed and not explained by the dose of VKA.

The impact of the CYP2C9 and VKORC1 polymorphisms on acenocoumarol dose requirements in a Romanian population

AIM

To investigate the genotype-phenotype correlation in Romanian patients treated with acenocoumarol.

MATERIAL AND METHODS

We studied 301 consecutive patients who required treatment with acenocoumarol, admitted within the Municipal Hospital of Cluj-Napoca and the Heart Institute "Niculae Stănciou" in Cluj-Napoca over a 3-year period. For each patient we recorded clinical parameters which could interfere with the achievement of stable therapeutic international normalized ratio (INR). We performed genetic analysis which consisted of genotyping the CYP2C9 gene and the VKORC1 gene. Patients were divided in three groups according to the acenocoumarol dose needed to reach a stable INR: the low dose group (≤7mg/week), the medium dose group (>7mg and <28mg/week) and the high acenocoumarol dose group (>28mg/week).

RESULTS

We found that patients' age was significantly different between groups (p<0.001). No differences existed between groups regarding the pathologies which required anticoagulation therapy or the concomitant treatment. The following parameters increased the odds of receiving a low dose of acenocoumarol: patient's age over 65years (OR, 3.2; p=0.01; 95%CI: 1.24-8.25), the presence of the CYP2C9*3 allele (OR, 3.4; p=0.006; 95%CI: 1.41-8.34), and the GA or AA genotype of c.-1639G>A polymorphism of VKORC1 (OR, 6.5; p=0.01; 95%CI: 1.38-30.5; respectively OR, 11.6; p=0.003; 95%CI: 2.26-59.58). A high acenocoumarol dose was less likely to be administered to an elderly patient (OR, 0.24; p=0.001; 95%CI: 0.1-0.56) or to a patient with the GA or AA genotype (OR, 0.2; p<0.001; 95CI%: 0.09-0.45; respectively OR, 0.05; p=0.006; 95%CI: 0.007-0.43).

CONCLUSION

The stable therapeutic dose of acenocoumarol is dependent of patient's age, the presence of the CYP2C9*3 allele and the c.-1639G>A polymorphism of VKORC1.

Minor bleeds alert for subsequent major bleeding in patients using vitamin K antagonists

Vitamin K antagonists (VKA) are effective in primary and secondary prevention of thromboembolism, but the associated risk of bleeding is an important limitation. The majority of bleeds are clinically mild. In this study, we assessed whether these minor bleeds are associated with major bleeding, when controlling for other important risk indicators, including the achieved quality of anticoagulation. For this, 5898 patients attending a specialized anticoagulation clinic were retrospectively studied for 1 year after initiation of VKA therapy. The risk of major bleeding was estimated using a multivariate piecewise exponential model with time-varying exposure for occurring minor bleeds. In patients with a minor bleed (N=1015) subsequent major bleeding occurred more frequently than in patients without a minor bleed (N=4883), with an incidence rate of 2·3 [95% confidence interval (CI) 1·4-3·7] vs. 1·2 per 100 person-years (95% CI 0·9-1·7). The adjusted relative risk of subsequent major bleeding after a minor bleed was 2·9 (95% CI 1·1-7·2, P =0·024). The percentage of time that a patient had an International Normalized Ratio (INR) above 5 was also independently associated with major bleeding, with a 2·2-fold increased risk in patients with at least 9% of time above INR 5 (95% CI 1·3-4·0, P=0·006). Minor bleeds alert for subsequent major bleeding, independent of the quality of anticoagulation.

Pharmacogenetics of acenocoumarol in patients with extreme dose requirements

SUMMARY BACKGROUND

There is currently intense debate as to whether pharmacogenetic algorithms for estimating the initial dose of coumarins provide a more accurate dose than the fixed-dose approach. Recently, it has been suggested that the greatest benefit of pharmacogenetic algorithms is observed in patients with extreme dose requirements.

OBJECTIVES

To identify clinical and genetic factors that better characterize patients who need extreme acenocoumarol doses for steady anticoagulation state.

PATIENTS/METHODS

We reviewed 9538 patients with a steady acenocoumarol dose from three Spanish hospitals, selecting 83 who took or= 30.00 mg week(-1) (p95). We also selected patients matched by gender and age taking 13.50-14.00 mg week(-1) (p50). We genotyped VKORC1 (rs9923231), CALU (rs1043550), GGCX (rs699664), CYP2C9 (rs1799853; rs1057910), CYP4F2 (rs2108622) and F7 (rs5742910) single-nucleotide polymorphisms (SNPs).

RESULTS

Comparison between p5 and p95 revealed five parameters with significant differences: body surface area (BSA) (P = 0.006), age, VKORC1, CYP2C9 and CYP4F2 genotypes (all P < 0.001). First VKORC1, and second, CYP2C9 SNPs played a strong effect by determining extreme doses, particularly in p95. Only one out of 203 p95 had the VKORC1 A-1639A genotype, but this subject was CYP2C9*1/*1. In contrast, nine out of 83 p5 carried the VKORC1 G-1639G genotype, although six of them were CYP2C9*3 homozygotes and another two were heterozygotes. Surprisingly, CYP4F2 V433M SNP displayed prevalences that suggest that its influence might only be evident when patients are treated with high doses.

CONCLUSION

Two clinical data, age and BSA, and three SNPs in the VKORC1, CYP2C9 and CYP4F2 genes strongly predict outlier patients treated with acenocoumarol.

VKORC1 -1639G>A and CYP2C9*3 are the major genetic predictors of phenprocoumon dose requirement

PURPOSE

Phenprocoumon, similar to other coumarin-derived anticoagulants, is associated with a large variation in the individual dose requirement to achieve stable anticoagulation. Polymorphisms in the vitamin K epoxide reductase complex subunit 1 (VKORC1) and the liver enzyme cytochrome P450 2C9 (CYP2C9) effectively account for the variability in warfarin and acenocoumarol response but are less well-defined pharmacogenetic predictors in phenprocoumon therapy.

METHODS

A retrospective study was performed on 185 outpatients attending anticoagulation clinics in Austria and Germany. These patients were genotyped for the VKORC1 -1639G>A and 3730G>A polymorphisms as well as for the CYP2C9 *2 and *3 polymorphisms using a reverse hybridisation-based teststrip assay.

RESULTS

The VKORC1 -1639A allele, which was present at a frequency of 41.4% in the study cohort, significantly reduced the mean weekly phenprocoumon dose by 3 mg (19%) in the heterozygous and by 6.7 mg (43%) in the homozygous state compared to wild-type carriers (15.5 +/- 6.8 mg, p < 0.0001). A stepwise multiple regression analysis revealed that VKORC1 -1639G>A, age and CYP2C9*3 were the major independent determinants of phenprocoumon dose, accounting for 14.2, 9.1 and 4.7% of its variability, respectively (p </= 0.0007). The CYP2C9*2 polymorphism had a marginal influence (1.4%) and failed to reach statistical significance (p = 0.062). The VKORC1 3730G>A genotype had no additional predictive power for individual dose variability.

CONCLUSION

Similar to warfarin and acenocoumarol, the VKORC1 -1639G>A polymorphism had the highest impact on the maintenance dose of phenprocoumon. The factor age was the second most important predictor and explained a greater percentage of the variability than CYP2C9 genotype.

VKORC1 and CYP2C9 allelic variants influence acenocoumarol dose requirements in Greek patients

Aim: To identify the frequencies of the polymorphisms CYP2C9*2, CYP2C9*3 and VKORC1-1639 G>A in the Greek population and investigate whether these polymorphisms and patient demographics (age, sex and comedication) could explain the interindividual variability of acenocoumarol dose requirements for efficient anticoagulation. Materials & methods: CYP2C9*2 (Arg144Cys), CYP2C9*3 (Ile359Leu) and VKORC1–1639G>A allelic variants were analyzed in 98 patients treated with acenocoumarol. Results: Allelic frequencies of CYP2C9*2, CYP2C9*3 and VKORC1A were found to be 0.155, 0.075 and 0.485, respectively. Carriership of at least one CYP2C9*3 allele led to the most pronounced reduction in the required mean dose (p < 0.0001). In contrast, the CYP2C9*2 allele played a minor role (p = 0.3). VKORC1 A/A patients needed approximately a third of the dose required by wild-type patients to achieve the target INR (p < 0.0001). Age was the only demographical factor significantly affecting acenocoumarol dose (p < 0.0001). In a multivariable regression model, CYP2C9, VKORC1 genotypes and age explained 55% of acenocoumarol dosing variability. Conclusion: VKORC1-1639G>A, CYP2C9*2 and CYP2C9*3 polymorphisms were found to predispose to acenocoumarol sensitivity in Greeks. Other hereditary and nongenetic parameters must be incorporated in an individualized dosing algorithm to achieve a safer anticoagulant effect.

Effects of CYP2C9 and VKORC1 on INR variations and dose requirements during initial phase of anticoagulant therapy

Introduction: Anticoagulants of the coumarin type are effective drugs for the treatment and prevention of thromboembolic diseases. However, they have a narrow therapeutic range and show inter- and intra-individual variability in dose requirement, largely conditioned by both environmental and genetic factors. Methods: This prospective study investigated, during the initial phase of acenocoumarol therapy, the effect of CYP2C9 variant alleles and VKORC1 haplotypes, single and in combination, in 220 Italians. Results: CYP2C9*3 was associated with a 25% dose reduction and an increased risk of over-anticoagulation (International Normalized Ratio [INR] > 6) on day 4. Two copies of the VKORC1*2 haplotype were associated with a 45% dose reduction and an increased risk of over-anticoagulation. Homozygosity for VKORC1*3 and VKORC1*4 was associated with an increased dose requirement and a reduced risk of over-anticoagulation. The VKORC1*3 or *4 plus CYP2C9*1 genotype combination was associated with the highest dose requirement and the lowest INR on day 4; VKORC1*2 plus CYP2C9*3 was associated with the lowest dose requirement, the highest INR and an increased risk of over-anticoagulation. Even though they spent approximately 50% of the time within the target therapeutic range, VKORC1*3 or *4 plus CYP2C9*1 carriers spent a large percentage of the remaining time below and carriers of VKORC1*2 plus CYP2C9*3 above the target range. Discussion: The determination of VKORC1*3 and VKORC1*4 haplotypes may be an important addition to CYP2C9 and VKORC1*2 genotyping to identify patients at risk of being outside the target range during initial anticoagulation with acenocoumarol.

Ethnic differences in the VKORC1 gene polymorphism and an association with warfarin dosage requirements in cardiovascular surgery patients

OBJECTIVES

Vitamin K epoxide reductase (VKORC1) is the drug target for inhibition by coumarin-based anticoagulant drugs such as warfarin. Warfarin therapy has been reported as a leading cause of drug-related hospitalization and there is therefore an urgent need to develop tests for better warfarin prescription. We report here the distribution of the intron 1 -136 T>C (1173 T>C intron) polymorphism of VKORC1, previously reported to be associated with warfarin maintenance dose in Caucasians and Japanese, in several ethnic populations from Japan and Israel, and describe its significance for warfarin dosage in Japanese cardiovascular surgery patients.

METHODS

Subjects consisted of 132 Japanese individuals and 341 Israeli individuals from four Jewish ethnic groups (86 Ashkenazi Jews, 95 Yemenite Jews, 73 Moroccan Jews and 87 Libyan Jews). In addition, 31 Japanese patients receiving warfarin therapy after cardiovascular surgery, maintained with a target International Normalized Ratio, were studied. The genotyping for the 1173 T>C intron polymorphism of VKORC1 was determined using rapid real-time PCR.

RESULTS

The allele frequency of the combined VKORC1 1173 CT and CC genotypes varied among the four Israeli ethnic groups and was, on average, much higher in the Israeli (0.728) than in the Japanese population (0.152). For the Japanese cardiovascular surgery patients, the maintenance dose of warfarin was significantly larger in the combined VKORC1 1173 TC and CC genotype group than in the 1173 TT genotype group (3.6 +/- 0.5 mg vs 2.8 +/- 0.7 mg, respectively; p = 0.02).

CONCLUSION

The frequencies of the intron 1 VKORC1 1173 T>C SNP show significant differences between ethnic groups and are associated with warfarin dose requirements for achieving a recommended International Normalized Ratio range in Japanese cardiovascular surgery patients. This study supports the example of warfarin as an appropriate model for applying personalized medicine for anticoagulant drugs, and highlights the importance of ethnicity in pharmacogenetics.

Pharmacogenetics of oral anticoagulants: the opportunity for individualized drug treatment of greater safety

Oral antivitamin K (AVK) anticoagulants are widely prescribed for the prophylaxis and treatment of a number of thromboembolic disorders. They constitute a major cause of iatrogenic accidents because of their narrow therapeutic index and consequently increase both thrombotic and bleeding risk; thus, regular monitoring is required. Patient and environmental factors affect the anticoagulation response and it has become evident that the wide interindividual variation in AVK response is also partly genetically determined. The main enzyme responsible for the metabolism of AVKs is hepatic cytochrome P450 CYP2C9. Vitamin K epoxide reductase complex subunit I (VKORC1) is a key enzyme in the vitamin K cycle; it is required to regenerate the cofactor essential for the activation of vitamin K-dependent clotting factors and is the target enzyme of AVK inhibition. Genetic variations affecting both CYP2C9 and VKORC1 are associated with variability in drug response and may explain differences in dose requirements. Genotyping for CYP2C9 and VKORC1 variants before initiation of treatment could allow clinicians to develop dosing protocols and identify patients at higher risk for AVK complications such as bleeding.

The genetic interaction between VKORC1 c1173t and calumenin a29809g modulates the anticoagulant response of acenocoumarol

BACKGROUND

The efficacy of oral anticoagulant therapy is largely conditioned by both environmental and genetic factors.

OBJECTIVES

To attempt to define the genetic profile involved in the response to this treatment.

PATIENTS AND METHODS

We selected 100 men younger than 75 years, with non-valvular atrial fibrillation, who started anticoagulation with acenocoumarol following the same protocol: 3 mg for three consecutive days. Then, doses were individually adjusted to achieve a steady International Normalized Ratio (INR). The basal plasma level and the level after 3 days were obtained, and the INR was determined. We studied five functional polymorphisms: FVII -323 Del/Ins, CYP2C*9, VKORC1 c1173t, calumenin (CALU) R4Q and CALU a29809g. The dose required for a steady INR was also recorded.

RESULTS

Only the VKORC1 genotype had significant impact on the efficacy of therapy. Carriers of the 1173t allele were significantly more sensitive to therapy for 3 days [INR 2.07 (1.59-2.87) vs. 1.74 (1.30-2.09); P = 0.015] and they needed lower acenocoumarol doses to stabilize their INR (15.8 +/- 5.6 vs. 19.5 +/- 6.0 mg week(-1); P = 0.004). Its effect was exacerbated by combination with the CALU a29809g polymorphism. Carriers of both variants (27% of the sample) achieved the highest INR [2.26 (1.70-3.32)] and required the lowest dose (14.1 +/- 5.1 mg week(-1)). This genetic profile was particularly relevant in patients with INR >or= 3.5 at the start of therapy (P = 0.005; odds ratio = 6.67, 95% confidence interval = 1.32-37.43).

CONCLUSIONS

Our results suggest that CALU a29809g might be a new genetic factor involved in the pharmacogenetics of anticoagulant therapy, and confirm that specific genetic profiles defined by different polymorphisms will determine the initial response and dose required to achieve a stable and safe INR.

Translating pharmacogenomics: challenges on the road to the clinic

Pharmacogenomics is one of the first clinical applications of the postgenomic era. It promises personalized medicine rather than the established "one size fits all" approach to drugs and dosages. The expected reduction in trial and error should ultimately lead to more efficient and safer drug therapy. In recent years, commercially available pharmacogenomic tests have been approved by the Food and Drug Administration (FDA), but their application in patient care remains very limited. More generally, the implementation of pharmacogenomics in routine clinical practice presents significant challenges. This article presents specific clinical examples of such challenges and discusses how obstacles to implementation of pharmacogenomic testing can be addressed.

[Clinical pharmacogenomics for CYP2C8 and CYP2C9: general concepts and application to the use of NSAIDs]

OBJECTIVE

To study the major mutations in genes CYP2C8 and CYP2C9, their frequency in populations of diverse ethnical descent, their analysis methods, and the major drugs with affected metabolism, with a special emphasis on NSAIDs.

METHOD

Repeated searches of Pubmed (January 1966-January 2006) and Scholar Google were performed. All searches were restricted to studies in humans, and papers not written in Spanish or English were excluded.

RESULTS

Ten allelic variants of CYP2C8 and 24 of CYP2C have been reported. Not all of them exert a relevant effect on drug metabolism. In Caucasians 22% of CYP2C8 genes and 31% of CYP2C9 genes have mutations. In Asians fewer than 1% and nearly 3% are mutated, respectively. Major identification methods include endonuclease digestion, PCR, pyrosequencing, and microarrays. Not all NSAIDs are exclusive substrates for CYP2C8/9. The usefulness of allelic variant analysis varies with each individual drug. The risk for digestive hemorrhage associated with the CYP2C9 genotype is particularly relevant when using aceclofenac, celecoxib, diclofenac, ibuprofen, indomethacin, lornoxicam, piroxicam, or naproxen.

CONCLUSIONS

Although CYP2C8/9 activity plays an essential role in the metabolism of and clinical response to many NSAIDs, the use of pharmacogenomic techniques is not equally useful for all these drugs.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

The pharmacogenetics of coumarin therapy

Vitamin K antagonists (coumarins) are widely-used oral anticoagulants for the prevention of venous thromboembolism and strokes. Wide inter-individual variation in dose response and frequent bleeds characterize the initiation of coumarin therapy. Over the past 10 years both genetic and nongenetic determinants of coumarin dose response have been identified. A comprehensive pharmacogenetics approach to warfarin therapy has the potential to improve the safety and efficiency of warfarin initiation.

The c.-1639G > A polymorphism of the VKORC1 gene is a major determinant of the response to acenocoumarol in anticoagulated patients

Much of the variability in the sensitivity to warfarin in anticoagulated patients is associated with the c.-1639G > A polymorphism of the vitamin K-epoxide reductase (VKORC1) gene. However, its association with the acenocoumarol dose in patients under anticoagulant therapy has not been studied. The c.-1639G > A genotype of VKORC1 was determined in 113 patients on stable anticoagulation requiring low (n = 42), medium (n = 42) or high (n = 21) acenocoumarol doses. To evaluate the association between acenocoumarol requirements and the c.-1639G > A variant, multivariate logistic regression models were fitted, adjusting for age, gender, and the c.430C > T and c.1075A > C variants of cytochrome P450 2C9 (CYP2C9). A total of 90.5% of the patients in the low acenocoumarol dose group carried the A allele of VKORC1:c.-1639G > A. The A allele independently increased the odds of requiring a low acenocoumarol dose [odds ratio (OR) 9.4; 95% confidence interval (CI) 1.9-46.4; P = 0.006], especially when the homozygous form was present (OR 44.2; 95% CI 5.5-354.6; P < 0.001). The A allele was less frequent in the high dose group showing an inverse association with the requirement for high doses (OR 0.04; 95% CI 0.01-0.22; P < 0.001). The A allele of the c.-1639G > A polymorphism of VKORC1 is therefore associated with a low-dose requirement for acenocoumarol in patients receiving anticoagulant therapy.

Pharmacogenetics of oral anticoagulants

The use of oral anticoagulants (OA) is problematic due to its association with hemorrhagic complications. OA metabolism relies on the CYP2C9 complex. Genetic variations compromising metabolic competence of this complex may explain the risk of excessive and hazardous anticoagulation. A pharmacogenetics-based approach to this issue could be beneficial for choosing adequate dose and duration of treatment, in addition to having a better understanding of pharmacological interactions to which OA are susceptible. However, evidence from several basic and clinical studies indicates that both a complicated system of regulation of expression of multiple genes and the influence of a wide variety of epigenetic factors could be responsible for adverse drug reactions associated with the use of OA. Emphasis on understanding the gene-environment interactions could attain new paths to facilitate the use of these important drugs in the quotidian clinical practice.

Fluctuations in coagulation activity among patients with atrial fibrillation who are stably anticoagulated

Atrial fibrillation is an important independent risk factor for stroke and increases the risk of systemic embolism. The individual risk depends on several clinical, environmental and biological factors. Additionally, a hypercoagulable state with abnormalities of hemostasia, thrombosis and platelet function have been observed in atrial fibrillation. This arrhythmia is also influenced by a disrupted circadian rhythm of hypercoagulable status implicated in the genesis of cardiovascular and cerebral diseases. The beneficial effect of oral anticoagulation therapy in atrial fibrillation has been confirmed by several studies. However, circadian variations in the degree of anticoagulation in these patients have also been described. In this review, the authors analyze the factors that might condition diurnal variations in thrombogenesis, hypercoagulability, and the extent of anticoagulation in patients with atrial fibrillation.

Contribution of CYP2C9 to variability in vitamin K antagonist metabolism

CYP2C9 is the third most important cytochrome P450 (CYP) in terms of number of drugs metabolised. A considerable amount of information on this isoform is now available with respect to its structural biology, the mechanisms by which it can be induced and the existence of a range of variant alleles, which are often functionally significant. CYP2C9 makes a very important contribution to metabolism of vitamin K antagonist anticoagulants, and is the main oxidising enzyme for S-warfarin and S-acenocoumarol as well as contributing to phenprocoumon metabolism. A large number of studies have now shown that CYP2C9 genotype predicts dose requirement for both warfarin and acenocoumarol, with a possible contribution for phenprocoumon. Patients with variant alleles are likely to require a lower dose and may be at risk of overcoagulation and resultant bleeding, especially during the induction phase of therapy. Although CYP2C9 genotype is clearly a predictor of vitamin K antagonist dose requirement, especially in Caucasian populations in whom variant alleles are common, a number of recent studies have shown that age, genotype for the gene encoding the target gene vitamin K epoxide reductase and concomitant drugs are equally important factors in determining dose. There is a need for prospective studies to assess the value of predicting dose requirement on the basis of all these factors, including the CYP2C9 genotype.

Ethnic differences in CYP2C9*2 (Arg144Cys) and CYP2C9*3 (Ile359Leu) genotypes in Japanese and Israeli populations

CYP2C9 is a major P450 2C enzyme, which hydroxylates about 16% of drugs that are in current clinical use and contributes to the metabolism of a number of clinically important substrate drugs such as warfarin. Ethnic differences in the genetic variation of CYP2C9 have been reported, and might be related to the frequencies of adverse reactions to drugs metabolized by CYP2C9 in different ethnic groups. In the present study, ethnic differences in the CYP2C9*2 and CYP2C9*3 allele distribution in Japanese and Israeli populations were evaluated using a newly developed oligonucleotide based DNA array (OligoArray(R)). The population studied consisted of 147 Japanese and 388 Israeli donors (100 Ashkenazi Jews, 99 Yemenite Jews, 100 Moroccan Jews and 89 Libyan Jews). The CYP2C9*2 [Arg144Cys (416 C>T), exon 3] and CYP2C9*3 [Ile359Leu (1061 A>C), exon 7] genotypes were determined using an OligoArray(R). The accuracy of genotyping by the OligoArray(R) was verified by the fluorescent dye-terminator cycle sequencing method. A Hardy-Weinberg test indicated equilibrium (chi(2)<3.84 is Hardy-Weinberg) in all populations. The CYP2C9*2 genotype (CC/CT+TT) was absent in Japanese (1/0) (OR 0.02), and its frequency was significant in Libyan Jews (0.697/0.303) (OR 2.13; 95% CI 1.07-4.24) compared with Ashkenazi Jews (0.83/0.17), Yemenite Jews (0.899/0.101), and Moroccan Jews (0.81/0.19). The frequencies of CYP2C9*3 genotype (AA/AC+CC) was significantly lower in Japanese (0.986/0.014) (OR 0.08), and was higher in Libyan Jews (0.652/0.348) (OR 3.03; 95% CI 1.5-6.1) and Moroccan Jews (0.77/0.23) (OR 1.69; 95% CI 0.62-3.48) compared with those in Ashkenazi Jews (0.85/0.15) and Yemenite Jews (0.849/0.151). Thus, the CYP2C9*2 (Arg144Cys) and CYP2C9*3 (Ile359Leu) variants were rare in the Japanese population, and showed different frequencies in the four Jewish ethnic groups examined.

Warfarin reversal

Warfarin is the most commonly used oral anticoagulant in the UK. It is associated with few side effects apart from haemorrhage. The most appropriate way to reverse the anticoagulant effect of warfarin depends on the clinical circumstances. In serious bleeding, rapid reversal is required, whereas in minor bleeding or asymptomatic over anticoagulation, a more leisurely approach is usually appropriate. This review discusses the current approaches to warfarin reversal in clinical practice. The development of a uniform approach to warfarin reversal in the Northern Region is described.

The risk of overanticoagulation in patients with cytochrome P450 CYP2C9*2 or CYP2C9*3 alleles on acenocoumarol or phenprocoumon

Cytochrome P4502C9 (CYP2C9) is the main enzyme implicated in coumarin anticoagulant metabolism. The variant alleles CYP2C9*2 and CYP2C9*3 are associated with an increased response to warfarin. However, an effect on acenocoumarol dose requirements appears to be absent for the CYP2C9*2 allele and the consequences for the metabolism of phenprocoumon have not yet been established. We investigated CYP2C9 polymorphisms in relation to the international normalized ratio (INR) during the first 6 weeks of treatment and its effect on the maintenance dose in a cohort of 1124 patients from the Rotterdam Study who were treated with acenocoumarol or phenprocoumon. There was a statistically significant difference in first INR between patients with variant genotypes and those with the wild-type. Almost all acenocoumarol-treated patients with a variant genotype had a significantly higher mean INR and had a higher risk of an INR > or = 6.0 during the first 6 weeks of treatment. A clear genotype-dose relationship was found for acenocoumarol-treated patients. For patients on phenprocoumon, no significant differences were found between variant genotypes and the wild-type genotype. Individuals with one or more CYP2C9*2 or CYP2C9*3 allele(s) require a significantly lower dose of acenocoumarol compared to wild-type patients. Phenprocoumon appears to be a clinically useful alternative in patients carrying the CYP2C9*2 and *3 alleles.

CATALYTIC ROLES OF CYP2C9 AND ITS VARIANTS (CYP2C9*2 AND CYP2C9*3) IN LORNOXICAM 5′-HYDROXYLATION

The effects of allelic variants of CYP2C9 (CYP2C9*2 and CYP2C9*3) on lornoxicam 5'-hydroxylation were studied using the corresponding variant protein expressed in baculovirus-infected insect cells and human liver microsomes of known genotypes of CYP2C9. The results of the baculovirus expression system showed that CYP2C9.3 gives higher K(m) and lower V(max) values for lornoxicam 5'-hydroxylation than does CYP2C9.1. In contrast, K(m) and V(max) values of CYP2C9.1 and CYP2C9.2 for the reaction were comparable. Lornoxicam 5'-hydroxylation was also determined in liver microsomes of 12 humans genotyped for the CYP2C9 gene (*1/*1, n = 7; *1/*2, n = 2; *1/*3, n = 2; *3/*3, n = 1). A sample genotyped as *3/*3 exhibited 8- to 50-fold lower intrinsic clearance for lornoxicam 5'-hydroxylation than did samples genotyped as *1/*1. However, the values for intrinsic clearance for *1/*3 were within the range of values exhibited by samples of *1/*1. In addition, no appreciable differences were observed in kinetic parameters for lornoxicam 5'-hydroxylation between *1/*1 and *1/*2. In conclusion, this study showed that lornoxicam 5'-hydroxylation via CYP2C9 was markedly decreased by the substitution of Ile359Leu (CYP2C9.3), whereas the effect of the substitution of Arg144Cys (CYP2C9.2) was nonexistent or negligible. Additional in vivo studies are required to confirm that individuals with homologous CYP2C9*3 allele exhibit impaired lornoxicam clearance.