Optimal dosing of warfarin and other coumarin anticoagulants: the role of genetic polymorphisms

Interethnic differences in drug response: projected impact of genetic variations in the Saudi population

Ethnicity is known to have an impact on drug responses. This is particularly important for drugs that have a narrow therapeutic window, nonlinearity in pharmacokinetics and are metabolized by enzymes that demonstrate genetic polymorphisms. However, most clinical trials are conducted among Caucasians, which might limit the usefulness of the findings of such studies for other ethnicities. The representation of participants from Saudi Arabia in global clinical trials is low. Therefore, there is a paucity of evidence to assess the impact of ethnic variability in the Saudi population on drug response. In this article, the authors assess the projected impact of genetic polymorphisms in drug-metabolizing enzymes and drug targets on drug response in the Saudi population.

CYP2C9 gen polimorfizmlerinin losartan kullanan hipertansif hastalarda tedavi yanıtı üzerine etkisi

Amaç: Bu çalışmada, anti-hipertansif olarak losartan kullanan hastalarda CYP2C9 polimorfizmlerinin tedavi yanıtı üzerine etkileri incelenmiştir. Yöntemler: Araştırmaya yeni tanı almış, evre 1 esansiyel hipertansiyonu olan 74 hasta dahil edildi. Bu hastalara tedavi öncesi ve losartan başlandıktan altı hafta sonra kan basıncı ölçümleri yapılarak elde edilen kan basıncı düşüşleri kaydedildi. Hastalardan ilk tanı sırasında alınmış olan kan örneklerinden DNA izolasyonu yapılarak CYP2C9 *2 ve *3 polimorfik alelleri için genetik analizler yapıldı. Polimorfik alelleri taşıyan bireyler ile yabanıl tip (wild-type) genotip taşıyıcılarının anti-hipertansif tedavi yanıtları karşılaştırıldı. Bulgular: CYP2C9*1*2 genotipine sahip hastalar, yabanıl tip genotipe sahip hastalar ile kıyaslandığında diyastolik kan basıncı için gruplar arasında istatistiksel açıdan anlamlı fark saptanmazken, sistolik kan basıncındaki düşüşün yabanıl tip genotipe sahip hastalarda daha belirgin olma eğiliminde olduğu görüldü. CYP2C9*1*3 genotipi ise tedavi sonuçlarında anlamlı bir değişikliğe neden olmadı. Sonuç: Bulgularımız, CYP2C9*1*2 polimorfizminin hipertansif hastaların losartan ile tedavisinde sistolik kan basıncı yanıtını etkileyebileceğini düşündürmektedir. Öte yandan, CYP2C9*1*3 genotipinin sistolik veya diyastolik kan basıncı yanıtlarıyla ilişkisi gösterilememiştir. Anahtar kelimeler: Hipertansiyon, losartan, CYP2C9, genetik polimorfizm, farmakogenetik

Evaluation of the status quo of polyphenols analysis: Part I-phytochemistry, bioactivity, interactions, and industrial uses

Phytochemicals, especially polyphenols, are gaining more attention from both the scientific community and food, pharmaceutical, and cosmetics industries due to their implications in human health. In this line, lately new applications have emerged, and of great importance is the selection of accurate and reliable analytical methods for better evaluation of the quality of the end-products, which depends on diverse process variables as well as on the matrices and on the physicochemical properties of different polyphenols. The first of a two-part review on polyphenols will address the phytochemistry and biological activities of different classes of polyphenols including flavonoids, lignans and flavanolignans, stilbenoids, tannins, curcuminoids, and coumarins. Moreover, the possible interactions of polyphenols and current and potential industrial applications of polyphenols are discussed.

Water Soluble Coumarin Quaternary Ammonium Chlorides: Synthesis and Biological Evaluation

In the present study, coumarin-bearing three pyridinium and three tetra-alkyl ammonium salts were synthesized. The compounds were fully characterized by ¹ H- and ¹³ C-NMR, LC/MS and IR spectroscopic methods and elemental analyses. The cytotoxic properties of all compounds were tested against human liver cancer (HepG2), human colorectal cancer (Caco-2) and non-cancer mouse fibroblast (L-929) cell lines. Some compounds performed comparable cytotoxicity with standard drug cisplatin. Antibacterial properties of the compounds were tested against Gram-negative Escherichia coli and Gram-positive Bacillus subtilis bacteria, but the compounds did not have any antibacterial effect against both bacteria. Enzyme inhibitory properties of all compounds were tested on the activities of human carbonic anhydrase I and II, and xanthine oxidase. All compounds inhibited both enzymes more effectively than standard drugs, acetazolamide and allopurinol, respectively. The biological evaluation results showed that ionic and water soluble coumarin derivatives are promising structures for further investigations especially on enzyme inhibition field.

Direct enantioselective allylic substitution of 4-hydroxycoumarin derivatives with branched allylic alcohols via iridium catalysis

An iridium catalysed direct asymmetric allylic substitution reaction of 4-hydroxycoumarin derivatives with allylic alcohols with remarkably high yields and excellent enantioselectivities was realized.

Pharmacogenetics of anticoagulants used for stroke prevention in patients with atrial fibrillation

Introduction: The inclusion of pharmacogenetics alongside clinical information in anticoagulant therapy offers the opportunity for a tailored approach to treatment according to individual patient characteristics. Areas covered: Literature was searched using PubMed database, focusing on pharmacogenetics of oral anticoagulants. Original research articles and review articles in English language were included in the literature reviewed. This article includes all information available for the genetic cause of inter-individual variability in anticoagulation response to oral anticoagulant drugs. The pharmacogenetics of VKAs and NOACs are described in detail. Expert opinion: There have been numerous studies focusing on the pharmacogenetics of VKAs, particularly warfarin. Current evidence suggests that known genetic and clinical factors explain a large proportion of the inter-individual variability in response to warfarin. Pharmacogenetic-based algorithms have been validated to determine their clinical utility with equivocal results. To date, only a limited number of mostly small studies on the pharmacogenetics of NOACs exists. The latter have highlighted genetic polymorphisms in specific genes that may affect clinical outcomes. Further evaluations of these polymorphisms are needed before firm conclusions can be drawn about the significance of pharmacogenetics on NOAC therapy.

Pharmacogenetics of Warfarin in a Diverse Patient Population

INTRODUCTION

Many warfarin-related genotypes have shown to impact the average daily warfarin (ADW) dose requirements; however, information in non-Caucasian populations is limited.

OBJECTIVES

To identify the frequencies of 4 warfarin-related gene polymorphisms in an ethnically diverse patient population and to examine their impact with other clinical variables on ADW dose requirements.

METHODS

Patients were recruited from 2 anticoagulation clinics in the Los Angeles area. Blood samples were collected and genotyped for vitamin K epoxide reductase (VKORC1), CYP2C9*2, CYP2C9*3, and CYP4F2 after informed consent. Charts were reviewed to collect demographic, clinical, and warfarin dosing data.

RESULTS

A total of 291 patients were included (120 Caucasians, 127 Hispanics, and 44 Asians). In patients with wild-type genotypes for VKORC1, CYP2C9*2, CYP2C9*3, and CYP4F2, the highest warfarin requirement was found in Caucasians, lower in Hispanics, and lowest in Asians. Homozygous VKORC1 variant carriers were detected in 15%, 15%, and 79% in Caucasians, Hispanics, and Asians, respectively. Progressive lowering of ADW doses were associated with each VKORC1 variant in Caucasians and Hispanics, but the results in wild-type/ heterozygote Asians were unclear. CYP2C9 variants were associated with lower ADW doses; frequencies of CYP2C9*2 and CYP2C9*3 mutations were higher in Caucasians than in Hispanics but rare to none in Asians. The frequencies of CYP4F2 variant were similar across all ethnicities, but their impact on warfarin dose requirement were insignificant. Clinical factors such as age, body surface area, history of coronary artery disease, deep vein thrombosis or atrial fibrillation, and concomitant amiodarone or HMG-CoA reductase inhibitors had varying impact on the ADW requirements in the ethnicities studied.

CONCLUSIONS

Our study demonstrated differences among 3 ethnic groups in terms of ADW dose requirements and the impact of associated clinical variables. The results suggest that a single model for all ethnicities may not provide the best performance in predicting warfarin dose requirements.

The pediatric acenocoumarol dosing algorithm: the Children Anticoagulation and Pharmacogenetics Study

Essentials A pediatric pharmacogenetic dosing algorithm for acenocoumarol has not yet been developed. We conducted a multicenter retrospective follow-up study in children in the Netherlands. Body surface area and indication explained 45.0% of the variability in dose requirement. Adding the genotypes of VKORC1, CYP2C9 and CYP2C18 to the algorithm increased this to 61.8%.

SUMMARY

Background The large variability in dose requirement of vitamin K antagonists is well known. For warfarin, pediatric dosing algorithms have been developed to predict the correct dose for a patient; however, this is not the case for acenocoumarol. Objectives To develop dosing algorithms for pediatric patients receiving acenocoumarol with and without genetic information. Methods The Children Anticoagulation and Pharmacogenetics Study was designed as a multicenter retrospective follow-up study in Dutch anticoagulation clinics and children's hospitals. Pediatric patients who used acenocoumarol between 1995 and 2014 were selected for inclusion. Clinical information and saliva samples for genotyping of the genes encoding cytochrome P450 (CYP) 2C9, vitamin K epoxide reductase complex subunit 1 (VKORC1), CYP4F2, CYP2C18 and CYP3A4 were collected. Linear regression was used to analyze their association with the log mean stable dose. A stable period was defined as three or more consecutive International Normalized Ratio measurements within the therapeutic range over a period of ≥ 3 weeks. Results In total, 175 patients were included in the study, of whom 86 had a stable period and no missing clinical information (clinical cohort; median age 8.9 years, and 49% female). For 80 of these 86 patients, genetic information was also available (genetic cohort). The clinical algorithm, containing body surface area and indication, explained 45.0% of the variability in dose requirement of acenocoumarol. After addition of the VKORC1, CYP2C9, and CYP2C18 genotypes to the algorithm, this increased to 61.8%. Conclusions These findings show that clinical factors had the largest impact on the required dose of acenocoumarol in pediatric patients. Nevertheless, genetic factors, and especially VKORC1, also explained a significant part of the variability.

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.

Treatment Satisfaction Questionnaire for Medication: Validation of the Translated Arabic Version among Patients Undergoing Warfarin Therapy in Saudi Arabia

OBJECTIVES

To validate the psychometric properties of the translated Arabic version of the Treatment Satisfaction Questionnaire for Medication (TSQM 1.4) for patients on warfarin therapy in Saudi anticoagulation clinics (ACCs).

METHODS

A cross-sectional survey was conducted at the Security Forces Hospital ACC in Riyadh, Saudi Arabia. It involved administering questionnaires related to patients' satisfaction and assessing adherence through interviews. The quality of the international normalized ratio control was assessed using the Rosendaal method. A psychometric evaluation of TSQM 1.4 was carried out, addressing internal consistency and known-groups and convergent validity.

RESULTS

A total of 101 patients completed the questionnaire with an 80% response rate. The independent Cronbach α values for the effectiveness, side effects, and global satisfaction domains were consistently higher than 0.75, demonstrating good internal consistency and suitability of these domains for application in the current patients' setting. When these domains were used together in a multivariable logistic regression model of adherence, the only domain that remained significant was TSQM effectiveness (P = 0.017). Interestingly, a higher likelihood of moderate to optimal international normalized ratio control was significantly and independently associated with increased satisfaction scores in the effectiveness and convenience domains, but not in the side effects and global satisfaction domains.

CONCLUSIONS

This study provides evidence in favor of the reliability and validity of the Arabic version of TSQM 1.4 as a useful measure of satisfaction with anticoagulant therapy in patients visiting ACCs. The TSQM subscales in this patient setting seem to detect a clinically meaningful change over time, enhancing the potential of their use in routine practice.

Effects of warfarin on biological processes other than haemostasis: A review

Warfarin is the world's most widely used anticoagulant drug. Its anticoagulant activity is based on the inhibition of the vitamin K-dependent (VKD) step in the complete synthesis of a number of blood coagulation factors that are required for normal blood coagulation. Warfarin also affects synthesis of VKD proteins not related to haemostasis including those involved in bone growth and vascular calcification. Antithrombotic activity of warfarin is considered responsible for some aspects of its anti-tumour activity of warfarin. Some aspects of activities against tumours seem not to be related to haemostasis and included effects of warfarin on non-haemostatic VKD proteins as well as those not related to VKD proteins. Inflammatory/immunomodulatory effects of warfarin indicate much broader potential of action of this drug both in physiological and pathological processes. This review provides an overview of the published data dealing with the effects of warfarin on biological processes other than haemostasis.

Pharmacogenetics: a general review on progress to date

BACKGROUND

Pharmacogenetics is not a new subject area but its relevance to drug prescribing has become clearer in recent years due to developments in gene cloning and DNA genotyping and sequencing.

SOURCES OF DATA

There is a very extensive published literature concerned with a variety of different genes and drugs.

AREAS OF AGREEMENT

There is general agreement that pharmacogenetic testing is essential for the safe use of drugs such as the thiopurines and abacavir.

AREAS OF CONTROVERSY

Whether pharmacogenetic testing should be applied more widely including to the prescription of certain drugs such as warfarin and clopidogrel where the overall benefit is less clear remains controversial.

GROWING POINTS

Personal genotype information is increasingly being made available directly to the consumer. This is likely to increase demand for personalized prescription and mean that prescribers need to take pharmacogenetic information into account. Projects such as 100 000 genomes are providing complete genome sequences that can form part of a patient medical record. This information will be of great value in personalized prescribing.

AREAS TIMELY FOR DEVELOPING RESEARCH

Development of new drugs targeting particular genetic risk factors for disease. These could be prescribed to those with an at risk genotype.

Binding between Saikosaponin C and Human Serum Albumin by Fluorescence Spectroscopy and Molecular Docking

Saikosaponin C (SSC) is one of the major active constituents of dried Radix bupleuri root (Chaihu in Chinese) that has been widely used in China to treat a variety of conditions, such as liver disease, for many centuries. The binding of SSC to human serum albumin (HSA) was explored by fluorescence, circular dichroism (CD), UV-vis spectrophotometry, and molecular docking to understand both the pharmacology and the basis of the clinical use of SSC/Chaihu. SSC produced a concentration-dependent quenching effect on the intrinsic fluorescence of HSA, accompanied by a blue shift in the fluorescence spectra. The Stern-Volmer equation showed that this quenching was dominated by static quenching. The binding constant of SSC with HSA was 3.72 × 10³ and 2.99 × 10³ L·mol(-1) at 26 °C and 36 °C, respectively, with a single binding site on each SSC and HSA molecule. Site competitive experiments demonstrated that SSC bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for SSC-HSA association. The energy transfer efficiency and binding distance between SSC and HSA was calculated to be 0.23 J and 2.61 nm at 26 °C, respectively. Synchronous fluorescence and CD measurements indicated that SSC affected HSA conformation in the SSC-HSA complex. Molecular docking supported the experimental findings in conformational changes, binding sites and binding forces, and revealed binding of SSC at the interface between subdomains IIA-IIB.

How Physicochemical Properties of Drugs Affect Their Metabolism and Clearance

In this chapter the transport proteins and enzymes of importance for drug clearance are discussed. The primary organ for drug metabolism is the liver and to reach the intracellular compartment of hepatocytes, orally administered drugs must cross both the intestinal wall and the cell membrane of the liver cells. Transport proteins present in the cellular membrane may facilitate or hinder the compounds crossing these cellular barriers and hence will influence to what extent compounds will reach the enzymes. Here, the enzymes and transport proteins of importance for drug clearance are discussed. The molecular features of importance for drug interactions with transport proteins and enzymes are analyzed and the possibility to predict molecular features vulnerable to enzymatic degradation is discussed. From detailed analysis of the current literature it is concluded that for interaction, both with transport proteins and enzymes, lipophilicity plays a major role. In addition to this property, molecular properties such as hydrogen bond acceptors and donors, charge, aromaticity and molecular size can be used to distinguish between routes of clearance.

Fragmentation pathways of synthetic and naturally occurring coumarin derivatives by ion trap and quadrupole time-of-flight mass spectrometry

RATIONALE

Synthetic and natural coumarin derivatives possess a wide range of biological activities. Fragmentation pathway studies are important in identifying both naturally occurring coumarins and synthetic coumarins with novel structures and properties.

METHODS

The fragmentation pathways of eleven coumarin derivatives are investigated by electrospray ionization (ESI) ion-trap mass spectrometry (ESI-ITMSⁿ ) and ESI quadrupole time-of-flight mass spectrometry (QTOFMS) in positive mode. Compounds 1-9 in this study were newly synthesized in our laboratory. Compounds 10 and 11 were isolated from the root of Zanthoxylum armatum.

RESULTS

The major fragmentation pathways for 11 coumarin derivatives are greatly affected by the heterocyclic ring structures and the side-chain substituents. Typical losses of small neutral molecules, such as CH₃ CH₂ OH, CH₂ =CH₂ , CO, and H₂ O, are observed for compounds 1-5. Compounds 6-9 share similar fragmentation pathways through losses of CO, aromatic rings, and the coumarin skeleton. The main product ions at m/z 205, 219, and 220 observed for compounds 10 and 11 are produced by the loss of C₅ H₁₂ O₂ , C₄ H₁₀ O₂ , and the C₄ H₉ O₂ radical, respectively.

CONCLUSIONS

The fragmentation pathways of 11 coumarin derivatives are elucidated based on ITMSⁿ and QTOFMS spectral data. Differences in the structures of the heterocyclic rings and side-chain substituents strongly affect the fragmentation pathways of the coumarins. The present results will facilitate further research into the fragmentation pathways and structural characterization of these classes of compounds with diverse structures. Copyright © 2015 John Wiley & Sons, Ltd.

Interethnic variability of CYP4F2 (V433M) in admixed population of Roma and Hungarians

AIMS

Pharmacogenetic based dosing recommendations are provided in FDA-approved warfarin label for Caucasians. Evidence of notable difference in dosing algorithms of under-represented populations forced us to explore the genetic variability of CYP4F2 gene in Roma and Hungarian populations.

PATIENTS AND METHODS

484 Roma, 493 Hungarian untreated subjects were genotyped for the CYP4F2*3 (rs2108622) variant by PCR-RFLP assay.

RESULTS AND DISCUSSION

We firstly report, that frequencies of the CYP4F2 rs2108622 GG, GA, AA genotypes and A allele in the Roma population were 46.5%, 42.6%, 10.9% and 32.2%; in Hungarians 50.1%, 42.2%, 7.7% and 22.8%, respectively. Bearing of two minor alleles of CYP4F2 missense variant (AA genotype) modestly explains inter-ethnic differences of studied populations (p<0.08). CYP4F2*3 (V433M) risk allele frequency of Roma (0.32) was in higher range, and of Hungarians (0.23) in lower range, as compared with other world populations.

CONCLUSIONS

Roma have an elevated chance for higher mean warfarin dose, besides a decreased risk of major bleeding events in long-term warfarin use.

Oral anticoagulation: a critique of recent advances and controversies

There have recently been significant advances in the field of oral anticoagulation, but these have also led to many controversies. Warfarin is still the commonest drug used for clotting disorders but its use is complicated owing to wide inter-individual variability in dose requirement and its narrow therapeutic index. Warfarin dose requirement can be influenced by both genetic and environmental factors. Two recent randomized controlled trials (RCTs) came to different conclusion regarding the utility of genotype-guided dosing; we critically explore the reasons for the differences. The new generation of oral anticoagulants have been demonstrated to be as efficacious as warfarin, but further work is needed to evaluate their safety in real clinical settings.

Monitoring thrombin generation and screening anticoagulants through pulse laser-induced fragmentation of biofunctional nanogold on cellulose membranes

Thrombin generation (TG) has an important part in the blood coagulation system, and monitoring TG is useful for diagnosing various health issues related to hypo-coagulability and hyper-coagulability. In this study, we constructed probes by using mixed cellulose ester membranes (MCEMs) modified with gold nanoparticles (Au NPs) for monitoring thrombin activity using laser desorption/ionization mass spectrometry (LDI-MS). The LDI process produced Au cationic clusters ([Au(n)](+); n = 1-3) that we detected through MS. When thrombin reacted with fibrinogen on the Au NPs-MCEMs, insoluble fibrin was formed, hindering the formation of Au cationic clusters and, thereby, decreasing the intensity of their signals in the mass spectrum. Accordingly, we incorporated fibrinogen onto the Au NPs-MCEMs to form Fib-Au NPs-MCEM probes to monitor TG with good selectivity (>1000-fold toward thrombin with respect to other proteins or enzymes) and sensitivity (limit of detection for thrombin of ca. 2.5 pM in human plasma samples). Our probe exhibited remarkable performance in monitoring the inhibition of thrombin activity by direct thrombin inhibitors. Analyses of real samples using our new membrane-based probe suggested that it will be highly useful in practical applications for the effective management of hemostatic complications.

Mesenteric venous thrombosis

Mesenteric vein thrombosis is increasingly recognized as a cause of mesenteric ischemia. Acute thrombosis commonly presents with abdominal pain and chronic type with features of portal hypertension. Contrast enhanced CT scan of abdomen is quite accurate for diagnosing and differentiating two types of mesenteric venous thrombosis. Prothrombotic state, hematological malignancy, and local abdominal inflammatory conditions are common predisposing conditions. Over the last decade, JAK-2 (janus kinase 2) mutation has emerged as an accurate biomarker for diagnosis of myeloproliferative neoplasm, an important cause for mesenteric venous thrombosis. Anticoagulation is the treatment of choice for acute mesenteric venous thrombosis. Thrombolysis using systemic or transcatheter route is another option. Patients with peritoneal signs or refractory to initial measures require surgical exploration. Increasing recognition of mesenteric venous thrombosis and use of anticoagulation for treatment has resulted in reduction in the need for surgery with improvement in survival.

Gastrointestinal hemorrhage in warfarin anticoagulated patients: incidence, risk factor, management, and outcome

Background. Warfarin reduces the incidence of thromboembolism but increases the risk of gastrointestinal bleeding (GIB). GIB during warfarin anticoagulation is rarely evaluated in Asian patients. Aims. This study aimed at investigating the incidence, risk factors, management, and outcome of GIB in Taiwanese patients treated with warfarin. Methods. We analyzed a cohort of warfarin anticoagulated patients between July 1993 and May 2012. Clinical data were retrieved in a chart-reviewing manner. Results. A total of 401 warfarin anticoagulated patients were enrolled. The incidence of GIB was 3.9% per patient-years. Multivariate analysis with Cox regression showed that age >65 years old (RR: 2.5, 95% CI: 1.2–5.5), a mean international normalized ratio >2.1 (RR: 2.1, 95% CI: 1.0–4.2), a history of GIB (RR: 5.1, 95% CI: 1.9–13.5), and cirrhosis (RR: 6.9, 95% CI: 2.0–24.5) were independent factors predicting GIB. 27.3% of the GIB patients had rebleeding after restarting warfarin while thromboembolic events were found in 16.7% of the patients discontinuing warfarin therapy. Conclusions. Warfarin was associated with a significant incidence of GIB in Taiwanese patients. The intensity of anticoagulation should be monitored closely during warfarin therapy, especially in patients with risk factors of GIB.

Effect of VKORC1, CYP2C9 and CYP4F2 genetic variants in early outcomes during acenocoumarol treatment

Aim: To analyze VKORC1, CYP2C9 and CYP4F2 polymorphisms in relation to the main outcomes in the first stages of acenocoumarol therapy. Patients & methods: Nine hundred and forty one patients who had started therapy and in whom time to stable dosage, time to over-anticoagulation and adverse events occurred during 3 first months were retrospectively analyzed. Results: VKORC1 AA patients needed fewer days to reach stable dosage (p = 0.017). International normalized ratio [INR] at 72 h, and VKORC1 and CYP2C9 genotypes conditioned INR values >2.5 (p < 0.001, p = 0.002 and p < 0.001, respectively), whereas CYP4F2 T carriers had a low risk of the same outcome (p = 0.009). In regards to combined genotypes, CYP4F2 had a significant effect on over-anticoagulation at the beginning of therapy except for the VKORC1 AA and CYP2C9*3 combination. Conclusion: In addition to VKORC1 and CYP2C9, CYP4F2 gene has a slight but significant role in reaching INR >2.5 during the first weeks of acenocoumarol therapy.

Original submitted 22 July 2013; Revision submitted 14 November 2013

A randomized trial of genotype-guided dosing of warfarin

BACKGROUND

The level of anticoagulation in response to a fixed-dose regimen of warfarin is difficult to predict during the initiation of therapy. We prospectively compared the effect of genotype-guided dosing with that of standard dosing on anticoagulation control in patients starting warfarin therapy.

METHODS

We conducted a multicenter, randomized, controlled trial involving patients with atrial fibrillation or venous thromboembolism. Genotyping for CYP2C9*2, CYP2C9*3, and VKORC1 (-1639G→A) was performed with the use of a point-of-care test. For patients assigned to the genotype-guided group, warfarin doses were prescribed according to pharmacogenetic-based algorithms for the first 5 days. Patients in the control (standard dosing) group received a 3-day loading-dose regimen. After the initiation period, the treatment of all patients was managed according to routine clinical practice. The primary outcome measure was the percentage of time in the therapeutic range of 2.0 to 3.0 for the international normalized ratio (INR) during the first 12 weeks after warfarin initiation.

RESULTS

A total of 455 patients were recruited, with 227 randomly assigned to the genotype-guided group and 228 assigned to the control group. The mean percentage of time in the therapeutic range was 67.4% in the genotype-guided group as compared with 60.3% in the control group (adjusted difference, 7.0 percentage points; 95% confidence interval, 3.3 to 10.6; P<0.001). There were significantly fewer incidences of excessive anticoagulation (INR ≥4.0) in the genotype-guided group. The median time to reach a therapeutic INR was 21 days in the genotype-guided group as compared with 29 days in the control group (P<0.001).

CONCLUSIONS

Pharmacogenetic-based dosing was associated with a higher percentage of time in the therapeutic INR range than was standard dosing during the initiation of warfarin therapy. (Funded by the European Commission Seventh Framework Programme and others; ClinicalTrials.gov number, NCT01119300.).

[Improvement of medication safety by identification of genetically predisposed subjects. Personalized clinical strategies and regulatory advices]

BACKGROUND

Because adverse drug events (ADEs) have a high socio-economic impact there is an urgent need for effective prevention. In addition to process-related avoidable errors personalised approaches for the prevention of ADEs should also focus on genetic polymorphisms as potential causative agents.

AIM

Using five case reports as examples therapeutic modalities are described to illustrate the clinical impact of prospective testing aimed at estimating the individual risk of susceptible subjects.

MATERIAL AND METHODS

The role of the HLA system, the cytochrome P450 family, other metabolic enzymes and transport proteins are described to illustrate the broad range of genetic susceptibility. It is shown, why, when and for whom pretherapeutic tests on genetic polymorphisms are recommended to reduce the risk of ADEs.

RESULTS

The determination of genetic susceptibility is already implemented in clinical practice prior to (1) carbamazepine therapy in south-east Asians and (2) treatment with abacavir independent of ethnicity. Before prescribing carbamazepine or abacavir, it is recommended that therapeutic decisions be based on these test results.

CONCLUSION

The broad application of personalised medicine used as an effective tool for minimizing ADE risks is limited by the evidence-based benefit for the patient on the one hand and the costs of the test on the other hand.

First report of warfarin dose requirements in patients possessing the CYP2C9*12 allele

BACKGROUND

Warfarin is the most frequently prescribed anticoagulant in North America and Europe. It is administered as a racemate, but S-warfarin is principally responsible for its anticoagulant activity. Cytochrome P450 (CYP) 2C9 is the enzyme primarily responsible for the metabolism of S-warfarin. Numerous variant alleles of CYP2C9 have been identified. The CYP2C9*12 (rs9332239) allele harbors a P489S substitution in CYP2C9 which has been shown to result in a 40% decline in catalytic activity in vitro.

CASES

Four Caucasian patients with a low mean weekly warfarin dose (MWWD) were genotyped for CYP2C9, VKORC1 and APOE variant alleles. None of the four patients carried the common CYP2C9 variant alleles (*2, *3, *5, *6, *7, *8, *9, *11, *13) despite a relatively low MWWD (23.4±7.94 mg) compared to 208 patients carrying the CYP29C9*1 genotype (32.2±12.65 mg). Given that CYP2C9*12 confers decreased in vitro activity to the enzyme, we investigated whether these patients carried this allele. All four patients were CYP2C9*12 CT heterozygotes. Individual comparisons with patients possessing the same VKORC1 and APOE genotypes also demonstrated lower dose requirements in the patients that possessed CYP2C9*12 allele.

CONCLUSIONS

There are no reports of the clinical impact of rs9332239 on CYP2C9 substrates. This is the first report of patients with the rare CYP2C9*12 genotype and lower warfarin dose requirements.