The largest prospective warfarin-treated cohort supports genetic forecasting

A review of a priori regression models for warfarin maintenance dose prediction

A number of a priori warfarin dosing algorithms, derived using linear regression methods, have been proposed. Although these dosing algorithms may have been validated using patients derived from the same centre, rarely have they been validated using a patient cohort recruited from another centre. In order to undertake external validation, two cohorts were utilised. One cohort formed by patients from a prospective trial and the second formed by patients in the control arm of the EU-PACT trial. Of these, 641 patients were identified as having attained stable dosing and formed the dataset used for validation. Predicted maintenance doses from six criterion fulfilling regression models were then compared to individual patient stable warfarin dose. Predictive ability was assessed with reference to several statistics including the R-square and mean absolute error. The six regression models explained different amounts of variability in the stable maintenance warfarin dose requirements of the patients in the two validation cohorts; adjusted R-squared values ranged from 24.2% to 68.6%. An overview of the summary statistics demonstrated that no one dosing algorithm could be considered optimal. The larger validation cohort from the prospective trial produced more consistent statistics across the six dosing algorithms. The study found that all the regression models performed worse in the validation cohort when compared to the derivation cohort. Further, there was little difference between regression models that contained pharmacogenetic coefficients and algorithms containing just non-pharmacogenetic coefficients. The inconsistency of results between the validation cohorts suggests that unaccounted population specific factors cause variability in dosing algorithm performance. Better methods for dosing that take into account inter- and intra-individual variability, at the initiation and maintenance phases of warfarin treatment, are needed.

Pharmacogenetic-guided dosing of coumarin anticoagulants: algorithms for warfarin, acenocoumarol and phenprocoumon

Coumarin derivatives, such as warfarin, acenocoumarol and phenprocoumon are frequently prescribed oral anticoagulants to treat and prevent thromboembolism. Because there is a large inter-individual and intra-individual variability in dose-response and a small therapeutic window, treatment with coumarin derivatives is challenging. Certain polymorphisms in CYP2C9 and VKORC1 are associated with lower dose requirements and a higher risk of bleeding. In this review we describe the use of different coumarin derivatives, pharmacokinetic characteristics of these drugs and differences amongst the coumarins. We also describe the current clinical challenges and the role of pharmacogenetic factors. These genetic factors are used to develop dosing algorithms and can be used to predict the right coumarin dose. The effectiveness of this new dosing strategy is currently being investigated in clinical trials.

Genomic architecture of pharmacological efficacy and adverse events

The pharmacokinetic and pharmacodynamic disciplines address pharmacological traits, including efficacy and adverse events. Pharmacogenomics studies have identified pervasive genetic effects on treatment outcomes, resulting in the development of genetic biomarkers for optimization of drug therapy. Pharmacogenomics-based tests are already being applied in clinical decision making. However, despite substantial progress in identifying the genetic etiology of pharmacological response, current biomarker panels still largely rely on single gene tests with a large portion of the genetic effects remaining to be discovered. Future research must account for the combined effects of multiple genetic variants, incorporate pathway-based approaches, explore gene-gene interactions and nonprotein coding functional genetic variants, extend studies across ancestral populations, and prioritize laboratory characterization of molecular mechanisms. Because genetic factors can play a key role in drug response, accurate biomarker tests capturing the main genetic factors determining treatment outcomes have substantial potential for improving individual clinical care.

Pharmacogenetics-based warfarin dosing in children

Clinical factors, demographic variables and variations in two genes, CYP2C9 and VKORC1, have been shown to contribute to the variability in warfarin dose requirements among adult patients. Less is known about their relative importance for dose variability in children. A few small studies have been reported, but the results have been conflicting, especially regarding the impact of genotypes. In this article, we critically review published pharmacogenetic-based prediction models for warfarin dosing in children, and present results from a head-to-head comparison of predictive performance in a distinct cohort of warfarin-treated children. Finally we discuss what properties a prediction model should have, and what knowledge gaps need to be filled, to improve warfarin therapy in children of all ages.

Is there a role for MDR1, EPHX1 and protein Z gene variants in modulation of warfarin dosage? a study on a cohort of the Egyptian population

BACKGROUND

There is considerable inter-individual variability in warfarin dosages necessary to achieve target therapeutic anticoagulation. Polymorphisms in genes, which master warfarin pharmacokinetics and pharmacodynamics, might influence warfarin dose variation. Genes encoding drug transporters, such as human multidrug resistance (MDR1), as well as epoxide hydrolase 1 (EPHX1), which is a putative subunit of the vitamin K epoxide reductase, and Protein Z (PZ), which is a vitamin K-dependent plasma glycoprotein, are among those candidate genes.

OBJECTIVE

The purpose of this study was to investigate the contribution of MDR1 C3435T, EPHX1 H139R and PZ A-13G gene polymorphisms in warfarin dose variation in a cohort of the Egyptian population.

METHODS

Eighty-four patients whose international normalized ratio (INR) was in the range of 2-3, 41 males and 43 females, with a mean (±SD) age of 40.9 (13.3) years were recruited into this study. MDR1 C3435T, EPHX1 H139R and PZ A-13G gene polymorphisms were detected by polymerase chain reaction-restriction fragment length polymorphism. Primarily, linear regression analysis, including the variables age, gender, MDR1 C3435T, EPHX1 H139R and combined MDR1 C3435T, EPHX1 H139R and PZ A-13G genotypes, was used to assess the effective factors for warfarin maintenance dose. Secondly, the previously examined cytochrome P450 (CYP) 2C9 A1075C and vitamin K epoxide reductase complex subunit 1 (VKORC1) C1173T were added to the regression analysis.

RESULTS

Warfarin dose/week was not influenced by each of the MDR1 C3435T, EPHX1 H139R, and PZ A-13G gene polymorphisms when examined separately. However, when these single nucleotide polymorphisms (SNPs) were combined, MDR1 TT/EPHX1 RH,RR/PZ AA subjects showed statistically significant increase in warfarin dose/week when compared with MDR1 CC/EPHX1 RH,RR/PZ AA subjects [median (25th-75th percentiles): 49.0 (42.0-59.5) vs. 35.0 (24.5-42.0) mg/week, respectively] (p = 0.014). In contrast, in the presence of wild-type EPHX1 HH, there was a decrease in warfarin dose/week in MDR1 TT subjects when compared with CT and CC subjects [median (25th-75th percentiles): 22.0 (17.5-30.6), 42.0 (35.0-49.0) and 42.0 (28.0-54.3) mg/week, respectively] (p = 0.005 and 0.030, respectively). Age had a significant contribution (p = 0.048) to the overall variability in warfarin dose. Calculated weekly dose = 52.928 - (0.289 × age) + (9.709 × combined genotype). The multivariate linear regression equation of warfarin maintenance dose accounted for about 8 % of variation in dose (R (2) = 0.079), age accounted for 5 % of variation, while combined genotypes added the extra 3 %. However, the new regression equation accounted for 20.9 % of variation in dose. Age accounted for 5 %, while VKORC1 C1173T accounted for an extra 13 % of variation and MDR1 C3435T accounted for the remaining 3 % of variation. Calculated dose = 64.909 - (0.282 × age) - (13.390 × VKORC1) - (7.164 × MDR1). Correlation analysis showed a close and significant relationship between the calculated and actual warfarin dose (r = 0.457; p < 0.0005).

CONCLUSION

Warfarin dose/week was significantly influenced by the combined MDR1 C3435T and EPHX1 H139R gene polymorphism since no polymorphism of PZ A-13G SNP was detected in our studied Egyptian population. Future studies with larger sample size will be needed to confirm our findings before definitive conclusions can be made.

Effect of CYP2C9-VKORC1 interaction on warfarin stable dosage and its predictive algorithm

This study aimed to identify the effect of CYP2C9-VKORC1 interaction on warfarin dosage requirement and its predictive algorithm by investigating four populations. Generalized linear model was used to evaluate the relationship between the interaction and warfarin stable dosage (WSD), whereas multiple linear regression analysis was applied to construct the WSD predictive algorithm. To evaluate the effect of CYP2C9-VKORC1 interaction on the predictive algorithms, we compared the algorithms with and without the interaction. The interaction was significantly associated with WSD in the Chinese and White cohorts (P values < 0.05). In the algorithms that considered the interaction, the predictive success rates improved by only 0.12% in the Chinese patients and by a maximum of 0.02% in the White patients under four different CYP2C9 classifications. Thus, VKORC1-CYP2C9 interaction can affect WSD. However, the discrepancy between the predictive results obtained using the predictive algorithm with and without CYP2C9-VKORC1 interaction was negligible and can therefore be disregarded.

We are all individuals... bioinformatics in the personalized medicine era

The medical landscape is evolving at a rapid pace, creating the opportunity for more personalized patient treatment and shifting the way healthcare is approached and thought about. With the availability of (epi)genome-wide, transcriptomic and proteogenomic profiling techniques detailed characterization of a disease at the level of the individual is now possible, offering the opportunity for truly tailored approaches for treatment and patient care. While improvements are still expected, the techniques and the basic analytical tools have reached a state that these can be efficiently deployed in both routine research and clinical practice. Still, some major challenges remain. Notably, holistic approaches, integrating data from several sources, e.g. genomic and epigenomic, will increase the understanding of the underlying biological concepts and provide insight into the causes, effects and effective solutions. However, creating and validating such a knowledge base, potentially for different levels of expertise, and integrating several data points into meaningful information is not trivial.

Warfarin pharmacogenetics

The cytochrome P450 (CYP) 2C9 and vitamin K epoxide reductase complex 1 (VKORC1) genotypes have been strongly and consistently associated with warfarin dose requirements, and dosing algorithms incorporating genetic and clinical information have been shown to be predictive of stable warfarin dose. However, clinical trials evaluating genotype-guided warfarin dosing produced mixed results, calling into question the utility of this approach. Recent trials used surrogate markers as endpoints rather than clinical endpoints, further complicating translation of the data to clinical practice. The present data do not support genetic testing to guide warfarin dosing, but in the setting where genotype data are available, use of such data in those of European ancestry is reasonable. Outcomes data are expected from an on-going trial, observational studies continue, and more work is needed to define dosing algorithms that incorporate appropriate variants in minority populations; all these will further shape guidelines and recommendations on the clinical utility of genotype-guided warfarin dosing.

Effects on bleeding complications of pharmacogenetic testing for initial dosing of vitamin K antagonists: a systematic review and meta-analysis

BACKGROUND

Although warfarin and other vitamin K antagonists (VKAs) are the most widely used oral anticoagulants for the prevention and treatment of thromboembolic events, a number of factors hamper their manageability, the most important being the inter-individual variability of the therapeutic dose requirement. Following the discovery of the influence of CYP2C9 and VKORC1 polymorphisms on VKA dose requirements, there has been interest in genotype-guided VKA dosing in order to reduce the risk of over-anticoagulation at the time of therapy initiation and hence the risk of bleeding, particularly prominent during the early days of treatment. To assess the impact on clinical outcomes of pharmacogenetic testing for initial VKA dosing, we have performed a systematic review and meta-analysis of the literature.

METHODS

MEDLINE, EMBASE and Cochrane databases were searched up to March 2014. Only randomized controlled trials comparing genotype-guided vs. clinically-guided warfarin dosing were included.

RESULTS

Nine trials including 2812 patients met the inclusion criteria and were pooled for meta-analytical evaluation. Risk of bias, assessed according to the Cochrane methodology, showed a low risk for the majority of domains analyzed in the included trials. A statistically significant reduction in the risk ratio (RR) for developing major bleeding events was observed in the pharmacogenetic-guided group compared with the control group (RR = 0.47; 95% CI, 0.23-0.96; P = 0.040).

CONCLUSIONS

The results of this meta-analysis show that genotype-guided initial VKA dosing is able to reduce serious bleeding events by approximately 50% compared with clinically-guided dosing approaches.

The impact of VKORC1-1639G > A genetic polymorphism upon warfarin dose requirement in different ethnic populations

OBJECTIVE

Published data on the association between vitamin K epoxide reductase complex 1 (VKORC1)-1639G > A polymorphism and warfarin dose requirement are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed.

METHODS AND RESULTS

Studies were identified in English-language articles by search of PubMed and Embase database (inception to July 2013). A total of 32 prospective clinical trials involving 5005 patients were identified and included for analysis. Overall, the weighted mean maintenance dosage of warfarin in patients with the -1639AA genotype decreased 2.62 mg/d compared with that in the -1639GG genotype patients (95% CI -3.10 to -2.14; P < 0.00001) when 24 eligible studies were pooled into the meta-analysis. Furthermore, significantly lower warfarin dose requirement was found in patients with GA genotype versus GG genotype (WMD, -1.32; 95% CI -1.67 to -0.96; P < 0.00001). In the subgroup analysis by ethnicity, statistically significant lower maintenance dosage of warfarin in patients with the AA genotype versus GG genotype were found in both Caucasians (WMD, -2.47; 95% CI -2.92 to -2.03; P < 0.00001) and Asians (WMD, -2.84; 95% CI -4.57 to -1.11; P = 0.001).

CONCLUSIONS

This meta-analysis indicated that the VKORC1-1639G > A genetic polymorphism is associated with the variation of interindividual warfarin dose requirement in different ethnic populations.

Pharmacogenetics role in the safety of acenocoumarol therapy

Vitamin K antagonists (VKAs) remain as the most prescribed drug for treatment and prevention of thrombotic disorders in many countries, despite the recent approval of the new oral anticoagulants (NOACs). Although effectiveness and safety of VKAs are tightly associated to maintaining the patient within the international normalised ratio (INR) therapeutic range (TWR), they have been likened to NOACs when patients are in good INR control (≥66% of TWR). Therefore, assessing the safety of patients should be a priority in the selection of the anticoagulation therapy. The aim of this study was to evaluate the association between CYP2C9*2, CYP2C9*3, VKORC1, CYP4F2*3, ABCB1 C3435T, APOE, CYP2C19*2 and CYP2C19*17 gene polymorphisms and treatment safety in 128 patients diagnosed with atrial fibrillation or venous thromboembolism during the initial first seven months of acenocoumarol therapy. After the first month, VKORC1-T-allele and APOE-E3/E3 genotype were independently associated to higher time above therapeutic range (TAR) and lower time below the therapeutic range (TBR). After seven months, VKORC1 T-allele predicted higher TAR, and was also associated to increased INR>4, particularly the TT-genotype (odds ratio [OR]: 32; 95% confidence interval [CI95%]: 6-175; p=810⁻⁵). C-alleles for CYP2C9*3 (OR: 5.5; CI95%: 1.8-17; p=0.003) and ABCB1 (OR: 8.9;CI95%: 1.1-70; p=0.039) independently influenced on INR>6 . Patients VKORC1-TT/ABCB1-C remained 26.8% [19.7-38.9] TAR, with associated relative risk (RR) for INR>4 1.8 higher (CI95%: 1.2-2.5; p=0.015). Patients VKORC1-TT also presented the highest risk of bleeding events (RR: 3.5;CI95%: 1.4-8.4; p=0,010). In conclusion, VKORC1, CYP2C9*3, APOE and ABCB1 genotypes should be considered in prevention of overanticoagulation and bleeding events in the initiation of acenocoumarol therapy.

Pharmacogenetics of chronic pain management

OBJECTIVE

The experience of chronic pain is one of the commonest reasons individuals seek medical attention, making the management of chronic pain a major issue in clinical practice. Drug metabolism and responses are affected by many factors, with genetic variations offering only a partial explanation of an individual's response. There is a paucity of evidence for the benefits of pharmacogenetic testing in the context of pain management.

DESIGN AND METHODS

We reviewed the literature between 2000 and 2013, and references cited therein, using various keywords related to pain management, pharmacology and pharmacogenetics.

RESULTS

Opioids continue to be the mainstay of chronic pain management. Several non-opioid based therapies, such as treatment with cannabinoids, gene therapy and epigenetic-based approaches are now available for these patients. Adjuvant therapies with antidepressants, benzodiazepines or anticonvulsants can also be useful in managing pain. Currently, laboratory monitoring of pain management patients, if performed, is largely through urine drug measurements.

CONCLUSIONS

Drug half-life calculations can be used as functional markers of the cumulative effect of pharmacogenetics and drug-drug interactions. Assessment of half-life and therapeutic effects may be more useful than genetic testing in preventing adverse drug reactions to pain medications, while ensuring effective analgesia. Definitive, mass spectrometry-based methods, capable of measuring parent drug and metabolite levels, are the most useful assays for this purpose. Urine drug measurements do not necessarily correlate with serum drug concentrations or therapeutic effects. Therefore, they are limited in their use in monitoring efficacy and toxicity.

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.

Pharmacogenomics: Current State-of-the-Art

The completion of the human genome project 10 years ago was met with great optimism for improving drug therapy through personalized medicine approaches, with the anticipation that an era of genotype-guided patient prescribing was imminent. To some extent this has come to pass and a number of key pharmacogenomics markers of inter-individual drug response, for both safety and efficacy, have been identified and subsequently been adopted in clinical practice as pre-treatment genetic tests. However, the universal application of genetics in treatment guidance is still a long way off. This review will highlight important pharmacogenomic discoveries which have been facilitated by the human genome project and other milestone projects such as the International HapMap and 1000 genomes, and by the continued development of genotyping and sequencing technologies, including rapid point of care pre-treatment genetic testing. However, there are still many challenges to implementation for the many other reported biomarkers which continue to languish within the discovery phase. As technology advances over the next 10 years, and the costs fall, the field will see larger genetic data sets, including affordable whole genome sequences, which will, it is hoped, improve patient outcomes through better diagnostic, prognostic and predictive biomarkers.

A model predicting fluindione dose requirement in elderly inpatients including genotypes, body weight, and amiodarone

Indandione VKAs have been widely used for decades, especially in Eastern Europe and France. Contrary to coumarin VKAs, the relative contribution of individual factors to the indandione-VKA response is poorly known. In the present multicentre study, we sought to develop and validate a model including genetic and non-genetic factors to predict the daily fluindione dose requirement in elderly patients in whom VKA dosing is challenging. We prospectively recorded clinical and therapeutic data in 230 Caucasian inpatients mean aged 85 ± 6 years, who had reached international normalized ratio stabilisation (range 2.0-3.0) on fluindione. In the derivation cohort (n=156), we analysed 13 polymorphisms in seven genes potentially involved in the pharmacological effect or vitamin-K cycle (VKORC1, CYP4F2, EPHX1) and fluindione metabolism/transport (CYP2C9, CYP2C19, CYP3A5, ABCB1). We built a regression model incorporating non-genetic and genetic data and evaluated the model performances in a separate cohort (n=74).Body-weight, amiodarone intake, VKORC1, CYP4F2, ABCB1 genotypes were retained in the final model, accounting for 31.5% of dose variability. None influence of CYP2C9 was observed. Our final model showed good performances: in 83.3% of the validation cohort patients, the dose was accurately predicted within 5 mg, i.e.the usual step used for adjusting fluindione dosage. In conclusion, in addition to body-weight and amiodarone-intake, pharmacogenetic factors (VKORC1, CYP4F2, ABCB1) related to the pharmacodynamic effect and transport of fluindione significantly influenced the dose requirement in elderly patients while CYP2C9 did not. Studies are required to know whether fluindione could be an alternative VKA in carriers of polymorphic CYP2C9 alleles, hypersensitive to coumarins.

Impact of CYP2C9 polymorphisms on the vulnerability to pharmacokinetic drug-drug interactions during acenocoumarol treatment

AIM

The objective of this study was to investigate the impact of CYP2C9 polymorphisms and drug-drug interactions on the risk of overanticoagulation in patients treated with acenocoumarol, a vitamin K antagonist.

MATERIALS & METHODS

A prospective observational study was performed on patients starting acenocoumarol (n = 115). CYP2C9 genotypes were assessed. Data on International Normalized Ratio, comedications and doses of acenocoumarol were collected during the first 35 days of therapy. Overanticoagulation was defined as the occurrence of at least one International Normalized Ratio ≥4.

RESULTS

The presence of a CYP2C9 inhibitor or a CYP2C9 polymorphisms statistically increased the risk of overanticoagulation (hazard ratio [HR]: 2.8, p < 0.001 and HR: 1.7, p = 0.04, respectively). The presence of CYP2C9 polymorphisms almost tripled the risk of overanticoagulation (HR: 2.91, p = 0.01) in the presence of a clinically significant drug-drug interaction.

CONCLUSION

These findings support the fact that CYP2C9 genotyping could be useful to identify patients requiring closer monitoring, especially when a drug-drug interaction is expected.

Association of gene polymorphisms with the risk of warfarin bleeding complications at therapeutic INR in patients with mechanical cardiac valves

WHAT IS KNOWN AND OBJECTIVE

Pharmacogenetic studies of the genetic regulation of warfarin dose requirement have been reported, but few have been on the bleeding complications at therapeutic international normalized ratio (INR). This study aimed to evaluate the effect of gene polymorphisms of CYP2C9, VKORC1, thrombomodulin (THBD) and C-reactive protein (CRP) on the risk of bleeding complications of warfarin at therapeutic INR in Korean patients with mechanical cardiac valves.

METHODS

A retrospective warfarin pharmacogenetic association study was performed. One hundred and forty-two patients with mechanical cardiac valves who were on warfarin anticoagulation therapy and maintained INR levels of 2·0-3·0 for 3 consecutive time intervals were followed up. CYP2C9 rs1057910, VKORC1 rs9934438, CRP rs1205, THBD rs1042580 and THBD rs3176123 were genotyped. The association between genotypes and warfarin bleeding complications was evaluated using logistic regression analysis, adjusted for demographic and clinical factors.

RESULTS AND DISCUSSION

Of 142 eligible patients, 21 patients (14·8%) had bleeding complications at therapeutic INR. Patients with the G allele in THBD rs1042580 (AG or GG) had a lower risk of bleeding than patients with the AA genotype (adjusted OR: 0·210, 95% CI: 0·050-0·875, P = 0·032). The THBD rs3176123 polymorphism did not show any association with bleeding. For CRP rs1205, patients with the A allele (GA or AA genotype) had a higher risk of bleeding than patients with the GG genotype (adjusted OR: 5·575, 95% CI: 1·409-22·058, P = 0·014). Variant VKORC1 and CYP2C9 genotypes did not confer a significant increase in the risk for bleeding complications.

WHAT IS NEW AND CONCLUSIONS

As expected, no association could be found between bleeding complications and two dose-related genes (CYP2C9*3 and VKORC1 rs9934438). In contrast, our results suggest that two genetic markers (THBD rs1042580 and CRP rs1205) could be predictors of bleeding complications of warfarin at normal INR. Given the retrospective study design and the relatively small sample size, our hypothesis requires further independent validation using more robust prospective designs. However, additional retrospective studies similar to ours but in populations with different genetic backgrounds should also be useful.

CYP2C9, VKORC1, CYP4F2, ABCB1 and F5 variants: influence on quality of long-term anticoagulation

AIMS

The study aims to evaluate the impact of genetic, demographic and clinical data on various measures of outcome of anticoagulation quality in patients.

PATIENTS AND METHODS

The study consisted of 310 patients receiving long-term oral anticoagulation therapy in our hospital. Apart from demographic and clinical variables, 21 SNPs (in 7 genes) were analyzed and compared with the outcomes of anticoagulation therapy. Various outcomes that were measured are; supra therapeutic INRs (INR >3, >6), anticoagulation stabilization, time taken to stabilize and proportion of INRs within (2-3), above (>3) and below (<2) therapeutic range.

RESULTS

Supra therapeutic INRs were influenced by CYP2C9*2, *3, CYP4F2 rs2108622, VKORC1-1639G>A, 1173C>T, rs55894764 along with concomitant drugs, smoking, body weight and height. Persistently fluctuating INRs/absolute instability correlated with VKORC1-1639G>A, gender, height and body mass index. The time taken to stabilize was associated with CYP4F2 rs2108622, CYP2C9*14, smoking, clinical indication and concomitant drugs. The overall distribution of INR was influenced by variants in CYP4F2 rs2108622, CYP2C9*3, rs9332230, VKORC1 1173C>T, -1639G>A, rs55894764, ABCB1 rs2032582, rs1128503, rs1045642 and F5 rs6025, age, smoking and concomitant drugs.

CONCLUSIONS

Knowledge of factors influencing the quality of long term anticoagulation can help clinicians to customize therapy either by dose variation, therapy with alternate choice of drug, concurrent heparin therapy and/or frequent INR monitoring.

Recent trends in the metabolism and cell biology of vitamin K with special reference to vitamin K cycling and MK-4 biosynthesis

In contrast to other fat-soluble vitamins, dietary vitamin K is rapidly lost to the body resulting in comparatively low tissue stores. Deficiency is kept at bay by the ubiquity of vitamin K in the diet, synthesis by gut microflora in some species, and relatively low vitamin K cofactor requirements for γ-glutamyl carboxylation. However, as shown by fatal neonatal bleeding in mice that lack vitamin K epoxide reductase (VKOR), the low requirements are dependent on the ability of animals to regenerate vitamin K from its epoxide metabolite via the vitamin K cycle. The identification of the genes encoding VKOR and its paralog VKOR-like 1 (VKORL1) has accelerated understanding of the enzymology of this salvage pathway. In parallel, a novel human enzyme that participates in the cellular conversion of phylloquinone to menaquinone (MK)-4 was identified as UbiA prenyltransferase-containing domain 1 (UBIAD1). Recent studies suggest that side-chain cleavage of oral phylloquinone occurs in the intestine, and that menadione is a circulating precursor of tissue MK-4. The mechanisms and functions of vitamin K recycling and MK-4 synthesis have dominated advances made in vitamin K biochemistry over the last five years and, after a brief overview of general metabolism, are the main focuses of this review.

Genetic risk factors for major bleeding in patients treated with warfarin in a community setting

The influence of warfarin pharmacogenomics on major bleeding risk has been little studied in long-term users and non-specialist care settings. We conducted a case-control study to evaluate associations between CYP2C9*2/*3, VKORC1(1173), and CYP4F2*3 variants and major bleeding among patients treated with warfarin in a community setting. We calculated major bleeding odds ratios, adjusting for race, duration of warfarin use, age, gender, and body mass index. In 265 cases and 305 controls with 3.4 and 3.7 mean years of warfarin use, respectively, CYP4F2*3 was associated with decreased major bleeding risk (odds ratio: 0.62; 95% confidence interval: 0.43-0.91). CYP2C9*2/*3 and VKORC1(1173) had null associations overall, but there was a nonsignificant increase in major bleeding risk in patients with duration <6 months (odds ratio: 1.30; 95% confidence interval: 0.60-2.83; odds ratio: 1.23; 95% confidence interval: 0.57-2.64, respectively). In summary, in the largest study of warfarin pharmacogenomics and major bleeding to date, we found a 38% lower risk in patients with CYP4F2*3, potentially reflecting interaction with warfarin and dietary vitamin K intake and warranting additional evaluation.

The VKORC1 Asp36Tyr variant and VKORC1 haplotype diversity in Ashkenazi and Ethiopian populations

The vitamin K epoxide reductase (VKORC1) is a key enzyme in the vitamin K cycle impacting various biological processes. VKORC1 genetic variability has been extensively studied in the context of warfarin pharmacogenetics revealing different distributions of VKORC1 haplotypes in various populations. We previously identified the VKORC1 Asp36Tyr mutation that was associated with warfarin resistance and with distinctive ethnic distribution. In this study, we performed haplotype analysis using Asp36Tyr and seven other VKORC1 markers in Ashkenazi and Ethiopian-Jewish and non-Jewish individuals. The VKORC1 variability was represented by nine haplotypes (V1-V9) that could be grouped into two distinct clusters (V1-V3 and V4-V9) with intra-cluster difference limited to two nucleotide changes. Phylogeny analysis suggested that these haplotypes could have developed from an ancestral variant, the common V8 haplotype (40 % in all population samples), after ten single mutation events. Asp36Tyr was exclusive to the V5 haplotype of the second cluster. Two haplotypes V5 and V4, distinguished only by Asp36Tyr, were prevalent in both Ethiopian population samples. The V2 haplotype, belonging to the first cluster, was the second most prevalent haplotype in the Ashkenazi population sample (15.8 %) but relatively uncommon in the Ethiopian origin (4.5-4.7 %). We discuss the genetic diversity among studied populations and its potential impact on warfarin-dose management in certain populations of African and European origin.

Prediction of optimal warfarin maintenance dose using advanced artificial neural networks

BACKGROUND

In recent years, pharmacogenetic algorithms were developed for estimating the appropriate dose of vitamin K antagonists.

AIM

To evaluate the performance of new generation artificial neural networks (ANNs) to predict the warfarin maintenance dose.

METHODS

Demographic, clinical and genetic data (CYP2C9 and VKORC1 polymorphisms) from 377 patients treated with warfarin were used. The final prediction model was based on 23 variables selected by TWIST® system within a bipartite division of the data set (training and testing) protocol.

RESULTS

The ANN algorithm reached high accuracy, with an average absolute error of 5.7 mg of the warfarin maintenance dose. In the subset of patients requiring ≤21 mg and 21-49 mg (45 and 51% of the cohort, respectively) the absolute error was 3.86 mg and 5.45 with a high percentage of subjects being correctly identified (71 and 73%, respectively).

CONCLUSION

ANN appears to be a promising tool for vitamin K antagonist maintenance dose prediction.

Inter and intra ethnic variation of vitamin K epoxide reductase complex and cytochrome P450 4F2 genetic polymorphisms and their prevalence in South Indian population

BACKGROUND:

Genetic variation in the vitamin K epoxide reductase complex (VKORC1) and cytochrome P450 4F2 (CYP4F2) genes were found to be strongly associated with the oral anticoagulant (OA) dose requirement. The distribution of genetic variation in these two genes was found to show large inter- and intra-ethnic difference.

MATERIALS AND METHODS:

A total of 470 unrelated, healthy volunteers of South Indians of either sex (age: 18-60 years) were enrolled for the study. A 5 ml of venous blood was collected and the genomic deoxyribonucleic acid (DNA) was extracted by using phenol-chloroform extraction method. Real-time quantitative polymerase chain reaction (RT-PCR) method was used for genotyping.

RESULTS:

The variant allele frequencies of VKORC1 rs2359612 (T), rs8050894 (C), rs9934438 (T) and rs9923231 (A) were found to be 11.0%, 11.8%, 11.7% and 12.0%, respectively. The variant allele VKORC1 rs7294 was (80.1%) more frequent and the variant allele CYP4F2 * 3 was found to be 41.8% in South Indians. The allele, genotype and haplotype frequencies of VKORC1 and CYP4F2 gene were distinct from other compared HapMap populations (P < 0.0001).

CONCLUSION:

The findings of our study provide the basic genetic information for further pharmacogenetic based investigation of OA therapy in the population.

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.).

A randomized trial of genotype-guided dosing of acenocoumarol and phenprocoumon

BACKGROUND

Observational evidence suggests that the use of a genotype-guided dosing algorithm may increase the effectiveness and safety of acenocoumarol and phenprocoumon therapy.

METHODS

We conducted two single-blind, randomized trials comparing a genotype-guided dosing algorithm that included clinical variables and genotyping for CYP2C9 and VKORC1 with a dosing algorithm that included only clinical variables, for the initiation of acenocoumarol or phenprocoumon treatment in patients with atrial fibrillation or venous thromboembolism. The primary outcome was the percentage of time in the target range for the international normalized ratio (INR; target range, 2.0 to 3.0) in the 12-week period after the initiation of therapy. Owing to low enrollment, the two trials were combined for analysis. The primary outcome was assessed in patients who remained in the trial for at least 10 weeks.

RESULTS

A total of 548 patients were enrolled (273 patients in the genotype-guided group and 275 in the control group). The follow-up was at least 10 weeks for 239 patients in the genotype-guided group and 245 in the control group. The percentage of time in the therapeutic INR range was 61.6% for patients receiving genotype-guided dosing and 60.2% for those receiving clinically guided dosing (P=0.52). There were no significant differences between the two groups for several secondary outcomes. The percentage of time in the therapeutic range during the first 4 weeks after the initiation of treatment in the two groups was 52.8% and 47.5% (P=0.02), respectively. There were no significant differences with respect to the incidence of bleeding or thromboembolic events.

CONCLUSIONS

Genotype-guided dosing of acenocoumarol or phenprocoumon did not improve the percentage of time in the therapeutic INR range during the 12 weeks after the initiation of therapy. (Funded by the European Commission Seventh Framework Programme and others; EU-PACT ClinicalTrials.gov numbers, NCT01119261 and NCT01119274.).

New oral anticoagulants and the cancer patient

Indications for anticoagulation are common in patients with malignancy. Cancer patients have an increased risk of developing venous thromboembolic events or may have other indications for anticoagulation, such as atrial fibrillation. New oral anticoagulants (NOACs) are now available that offer increased options for anticoagulation beyond the traditional vitamin K antagonists and low molecular weight heparins that have long been the cornerstone of treatment. This review will focus on the three NOACs that are currently approved for use in the U.S.: the direct thrombin inhibitor, dabigatran, and the factor Xa inhibitors, apixaban and rivaroxaban. Oncologists are likely to encounter an increasing number of patients taking these agents at the time of their cancer diagnosis or to have patients who develop indications for anticoagulation during the course of their disease. The basic pharmacology, current clinical indications, and approach to the use of NOACs in the cancer patient will be reviewed.

Improved accuracy of anticoagulant dose prediction using a pharmacogenetic and artificial neural network-based method

BACKGROUND

The unpredictability of acenocoumarol dose needed to achieve target blood thinning level remains a challenge. We aimed to apply and compare a pharmacogenetic least-squares model (LSM) and artificial neural network (ANN) models for predictions of acenocoumarol dosing.

METHODS

LSM and ANN models were used to analyze previously collected data on 174 participants (mean age: 67.45 SD 13.49 years) on acenocoumarol maintenance therapy. The models were based on demographics, lifestyle habits, concomitant diseases, medication intake, target INR, and genotyping results for CYP2C9 and VKORC1. LSM versus ANN performance comparisons were done by two methods: by randomly splitting the data as 50 % derivation and 50 % validation cohort followed by a bootstrap of 200 iterations, and by a 10-fold leave-one-out cross-validation technique.

RESULTS

The ANN-based pharmacogenetic model provided higher accuracy and larger R value than all other LSM-based models. The accuracy percentage improvement ranged between 5 % and 24 % for the derivation cohort and between 12 % and 25 % for the validation cohort. The increase in R value ranged between 6 % and 31 % for the derivation cohort and between 2 % and 31 % for the validation cohort. ANN increased the percentage of accurately dosed subjects (mean absolute error ≤1 mg/week) by 14.1 %, reduced the percentage of mis-dosed subjects (mean absolute error 2-3 mg/week) by 7.04 %, and reduced the percentage of grossly mis-dosed subjects (mean absolute error ≥4 mg/week) by 24 %.

CONCLUSIONS

ANN-based pharmacogenetic guidance of acenocoumarol dosing reduces the error in dosing to achieve target INR. These results need to be ascertained in a prospective study.

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.

Variability of warfarin dose response associated with CYP2C9 and VKORC1 gene polymorphisms in Chinese patients

OBJECTIVE

To investigate the prevalence and implication of cytochrome P450, family 2, subfamily C, polypeptide 9 (CYP2C9) variants and vitamin K epoxide reductase complex, subunit 1 (VKORC1)-1639 G > A polymorphisms in Chinese patients receiving warfarin therapy.

METHODS

Chinese Han patients requiring oral warfarin therapy were consecutively enrolled. Correlations between CYP2C9*1, *2, *3, *4, *5 variants and VKORC1-1639 G > A polymorphisms, fourth-day international normalized ratios (INRs) and warfarin maintenance dose were investigated.

RESULTS

Out of 101 patients, there were no significant differences in fourth-day INR or warfarin daily maintenance doses between patients with CYP2C9*1*1 and CYP2C9*1*3 genotypes. Patients with the VKORC1-1639 AA genotype had a higher fourth-day INR (1.87 ± 0.14) than those with the VKORC1-1639 AG genotype (1.32 ± 0.15). Warfarin maintenance dose for patients with the VKORC1-1639 AA genotype (2.40 ± 0.70 mg/day) was significantly lower than for patients with the VKORC1-1639 AG genotype (4.83 ± 0.70 mg/day).

CONCLUSIONS

Unlike Caucasian populations, VKORC1-1639 G > A polymorphisms in the Chinese population may be the dominant genetic factors associated with warfarin response variability.

Pharmacogenomics and cardiovascular disease

Variability in drug responsiveness is a sine qua non of modern therapeutics, and the contribution of genomic variation is increasingly recognized. Investigating the genomic basis for variable responses to cardiovascular therapies has been a model for pharmacogenomics in general and has established critical pathways and specific loci modulating therapeutic responses to commonly used drugs such as clopidogrel, warfarin, and statins. In addition, genomic approaches have defined mechanisms and genetic variants underlying important toxicities with these and other drugs. These findings have not only resulted in changes to the product labels but also have led to development of initial clinical guidelines that consider how to facilitate incorporating genetic information to the bedside. This review summarizes the state of knowledge in cardiovascular pharmacogenomics and considers how variants described to date might be deployed in clinical decision making.

Improvement of adequate use of warfarin for the elderly using decision tree-based approaches

OBJECTIVES

Due to the narrow therapeutic range and high drug-to-drug interactions (DDIs), improving the adequate use of warfarin for the elderly is crucial in clinical practice. This study examines whether the effectiveness of using warfarin among elderly inpatients can be improved when machine learning techniques and data from the laboratory information system are incorporated.

METHODS

Having employed 288 validated clinical cases in the DDI group and 89 cases in the non-DDI group, we evaluate the prediction performance of seven classification techniques, with and without an Adaptive Boosting (AdaBoost) algorithm. Measures including accuracy, sensitivity, specificity and area under the curve are used to evaluate model performance.

RESULTS

Decision tree-based classifiers outperform other investigated classifiers in all evaluation measures. The classifiers supplemented with AdaBoost can generally improve the performance. In addition, weight, congestive heart failure, and gender are among the top three critical variables affecting prediction accuracy for the non-DDI group, while age, ALT, and warfarin doses are the most influential factors for the DDI group.

CONCLUSION

Medical decision support systems incorporating decision tree-based approaches improve predicting performance and thus may serve as a supplementary tool in clinical practice. Information from laboratory tests and inpatients' history should not be ignored because related variables are shown to be decisive in our prediction models, especially when the DDIs exist.

Clopidogrel and warfarin pharmacogenetic tests: what is the evidence for use in clinical practice?

PURPOSE OF REVIEW

To review the most promising genetic markers associated with the variability in the safety or efficacy of warfarin and clopidogrel and highlight the verification and validation initiatives for translating clopidogrel and warfarin pharmacogenetic tests to clinical practice.

RECENT FINDINGS

Rapid advances in pharmacogenetics, continuous decrease in genotyping cost, development of point-of-care devices and the newly established clinical genotyping programs at several institutions hold the promise of individualizing clopidogrel and warfarin based on genotype. Guidelines have been established to assist clinicians in prescribing clopidogrel or warfarin dose based on genotype. However, the clinical utility of clopidogrel and warfarin is still limited. Accordingly, large randomized clinical trials are underway to define the role of clopidogrel and warfarin pharmacogenetics in clinical practice.

SUMMARY

Pharmacogenetics has offered compelling evidence toward the individualization of clopidogrel and warfarin therapies. The rapid advances in technology make the clinical implementation of clopidogrel and warfarin pharmacogenetics possible. The clinical genotyping programs and the ongoing clinical trials will help in overcoming some of the barriers facing the clinical implementation of clopidogrel and warfarin pharmacogenetics.

Applied pharmacogenomics in cardiovascular medicine

Interindividual heterogeneity in drug response is a central feature of all drug therapies. Studies in individual patients, families, and populations over the past several decades have identified variants in genes encoding drug elimination or drug target pathways that in some cases contribute substantially to variable efficacy and toxicity. Important associations of pharmacogenomics in cardiovascular medicine include clopidogrel and risk for in-stent thrombosis, steady-state warfarin dose, myotoxicity with simvastatin, and certain drug-induced arrhythmias. This review describes methods used to accumulate and validate these findings and points to approaches--now being put in place at some centers--to implementing them in clinical care.

Impact of genotype-guided dosing on anticoagulation visits for adults starting warfarin: a randomized controlled trial

Aim: This study aimed to assess the effectiveness of genotype-guided warfarin dosing. Patients & methods: A total of 109 adults were randomized to receive initial dosing as determined by an algorithm containing genetic (VKORC1 and CYP2C9) plus clinical information or only clinical information. Primary end points were the number of anticoagulation visits and the time in therapeutic range (TTR) over 90 days. Secondary end points included time to therapeutic dose, International Normalized Ratios of >4, emergency visits, hospitalizations, hemorrhagic events, thrombotic events and mortality. Results: Neither primary end point was significantly different between groups (anticoagulation visits: 6.96 vs 6.37, p = 0.51; TTR: 0.40 vs 0.43, p = 0.59). Fewer emergency visits, hospitalizations, major hemorrhagic events, thrombotic events and deaths occurred in the genetic plus clinical group than in the clinical only group, but these differences were not statistically significant. Conclusion: Genotype-guided dosing did not decrease the number of anticoagulation visits or improve TTR. Our trial was not powered to detect anything but large differences for utilization and health outcomes.

Original submitted 7 January 2013; Revision submitted 27 July 2013

Cost-effectiveness of pharmacogenetics-guided warfarin therapy vs. alternative anticoagulation in atrial fibrillation

Pharmacogenetics-guided warfarin dosing is an alternative to standard clinical algorithms and new oral anticoagulants for patients with nonvalvular atrial fibrillation. However, clinical evidence for pharmacogenetics-guided warfarin dosing is limited to intermediary outcomes, and consequently, there is a lack of information on the cost-effectiveness of anticoagulation treatment options. A clinical trial simulation of S-warfarin was used to predict times within therapeutic range for different dosing algorithms. Relative risks of clinical events, obtained from a meta-analysis of trials linking times within therapeutic range with outcomes, served as inputs to an economic analysis. Neither dabigatran nor rivaroxaban were cost-effective options. Along the cost-effectiveness frontier, in relation to clinically dosed warfarin, pharmacogenetics-guided warfarin and apixaban had incremental cost-effectiveness ratios of £13,226 and £20,671 per quality-adjusted life year gained, respectively. On the basis of our simulations, apixaban appears to be the most cost-effective treatment.

The impact of interacting drugs on dispensed doses of warfarin in the Swedish population: A novel use of population based drug registers

To investigate the impact of interacting drugs on the dispensed doses of warfarin in the Swedish population. This was a retrospective, cross-sectional population based register study of patients being dispensed warfarin. Warfarin doses were estimated in different age groups, in men and women, and in patients using interacting drugs. The influence of interacting drugs on the dispensed warfarin dose was analyzed using multiple regression. All 143,729 patients dispensed warfarin were analyzed. The dispensed dose of warfarin was highest in patients 30-39 years old and decreased with age. Co-medication with carbamazepine, simvastatin, paracetamol, amiodarone, fluconazole, lactulose, or bezafibrate was associated with significant changes in dispensed warfarin doses, by +40%, -3.4%, -7.3%, -8.2%, -8.8%, -9.0%, and -9.7%, respectively. After adjustment for age and gender, sulfamethoxazole was also found to significantly alter the dispensed warfarin dose (-6.1%). We provide new support for the previous scarce evidence of interactions between warfarin and carbamazepine, bezafibrate, and lactulose. Initiation or discontinuation of bezafibrate or lactulose in a patient on warfarin should warrant close clinical monitoring. The marked increased warfarin requirement associated with carbamazepine use supports moving from a more conservative reactive towards a proactive strategy including preventive warfarin dose adjustments to avoid potential adverse effects.

Effect of CYP2C9, VKORC1, CYP4F2 and GGCX genetic variants on warfarin maintenance dose and explicating a new pharmacogenetic algorithm in South Indian population

OBJECTIVE

To determine the influence of genetic polymorphisms on warfarin maintenance dose and to explicate an algorithm using the pharmacogenetic and clinical factors to determine the maintenance and/or starting dose of warfarin in South Indian patients receiving warfarin therapy.

METHODS

Patients receiving stabilized warfarin therapy (n=257) were included in the study. Single nucleotide polymorphisms (SNPs) of CYP2C9 (rs1799853 and rs1057910), VKORC1 (rs9923231, rs7196161, rs2884737, rs9934438, rs8050894, rs2359612 and rs7294), CYP4F2 (rs2108622) and GGCX (rs11676382) were genotyped by the quantitative real time-PCR method.

RESULTS

The mean daily maintenance dose of warfarin was found to be 4.7 ± 2.1 mg/day. Patients with the CYP2C9*1/*2, *1/*3 and *2/*3 variant genotypes required a 51.0 (2.8 mg), 60.9 (2.3 mg) and 62.2 % (2.2 mg) lower daily maintenance dose of warfarin, respectively, than those patients with the CYP2C9*1/*1 wild-type genotype (5.2 mg) (p<0.0001). The genetic variants of CYP2C9, VKORC1 and GGCX were associated with decreased warfarin dose, except for rs7196161, rs7294 and rs2108622 which were associated with an increased warfarin dose. Genetic variations of CYP2C9 (*2 and *3), VKORC1 (rs9923231, rs7294, rs9934438 and rs2359612), CYP4F2, GGCX and non-genetic factors such as age, body weight, clinical status (post mechanical valve replacement) could explain up to 62.1 % of the overall variation (adjusted r (2) 60.2 %, p<0.0001) in warfarin maintenance dose.

CONCLUSION

Genetic polymorphisms of CYP2C9, VKORC1, CYP4F2 and GGCX are important predictive factors of warfarin maintenance dose, and the developed algorithm will be useful to predict the required maintenance and/or starting warfarin dose in South Indian populations.

Ethnicity-specific pharmacogenetics: the case of warfarin in African Americans

Using a derivation cohort (N=349), we developed the first warfarin dosing algorithm that includes recently discovered polymorphisms in VKORC1 and CYP2C9 associated with warfarin dose requirement in African Americans (AAs). We tested our novel algorithm in an independent cohort of 129 AAs and compared the dose prediction to the International Warfarin Pharmacogenetics Consortium (IWPC) dosing algorithms. Our algorithm explains more of the phenotypic variation (R(2)=0.27) than the IWPC pharmacogenomics (R(2)=0.15) or clinical (R(2)=0.16) algorithms. Among high-dose patients, our algorithm predicted a higher proportion of patients within 20% of stable warfarin dose (45% vs 29% and 2% in the IWPC pharmacogenomics and clinical algorithms, respectively). In contrast to our novel algorithm, a significant inverse correlation between predicted dose and percent West African ancestry was observed for the IWPC pharmacogenomics algorithm among patients requiring ⩾60 mg per week (β=-2.04, P=0.02).

Value-based assessment of pharmacodiagnostic testing from early stage development to real-world use

Disease etiology may be regarded as a consequence of both genotypic and biochemical phenomena, which impact individual patients in different ways. Disease prognosis, beneficial treatment response, and susceptibility to adverse drug effects are often intimately tied to individual biology. Clinical and genetic biomarkers applied individually or in concert are increasingly used to stratify patient populations in terms of prognosis, therapeutic benefit, or safety. As a result, clinical trialists are challenged to design studies that reflect these determinants of outcome, to optimize the patient's eventual clinical course both in the trial and in actual practice. These designs are informed both by preclinical studies and by real-world research that can establish proof of concept for a novel biomarker and provide a basic understanding of the relationship between biomarker and clinical outcome. As clinical and real-world studies unfold, a deeper understanding of the nature of the biomarker and its potential uses in drug development is gained. Specifically, one can eventually define the biomarker as prognostic (i.e., predicts disease progression), predictive (predicts treatment response or adverse outcome(s)), or exhibiting both prognostic and predictive properties. One must further validate the performance of these emerging biomarkers, again in both the trial and real-world environments. The eventual adoption of the biomarker as a useful pharmacodiagnostic test is premised upon this early translational research. In this article, the development and validation of predictive and prognostic biomarkers is discussed by using selected examples that highlight factors contributing to the valuation of biomarkers and their application to personalized medicine in the real world.

Pharmacogenetics in clinical pediatrics: challenges and strategies

The use of genetic information to guide medication decisions holds great promise to improve therapeutic outcomes through increased efficacy and reduced adverse events. As in many areas of medicine, pediatric research and clinical implementation in pharmacogenetics lag behind corresponding adult discovery and clinical applications. In adults, genotype-guided clinical decision support for medications such as clopidogrel, warfarin and simvastatin are in use in some medical centers. However, research conducted in pediatric populations demonstrates that the models and practices developed in adults may be inaccurate in children, and some applications lack any pediatric research to guide clinical decisions. To account for additional factors introduced by developmental considerations in pediatric populations and provide pediatric patients with maximal benefit from genotype-guided therapy, the field will need to develop and employ creative solutions. In this article, we detail some concerns about research and clinical implementation of pharmacogenetics in pediatrics, and present potential mechanisms for addressing them.