Rianne M. F. van Schie

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.).

Genotype-guided dosing of coumarin derivatives: the European pharmacogenetics of anticoagulant therapy (EU-PACT) trial design

The narrow therapeutic range and wide interpatient variability in dose requirement make anticoagulation response to coumarin derivatives unpredictable. As a result, patients require frequent monitoring to avert adverse effects and maintain therapeutic efficacy. Polymorphisms in VKORC1 and CYP2C9 jointly account for about 40% of the interindividual variability in dose requirements. To date, several pharmacogenetic-guided dosing algorithms for coumarin derivatives, predominately for warfarin, have been developed. However, the potential benefit of these dosing algorithms in terms of their safety and clinical utility has not been adequately investigated in randomized settings. The European Pharmacogenetics of Anticoagulant Therapy (EU-PACT) trial will assess, in a single-blinded and randomized controlled trial with a follow-up period of 3 months, the safety and clinical utility of genotype-guided dosing in daily practice for the three main coumarin derivatives used in Europe. The primary outcome measure is the percentage time in the therapeutic range for international normalized ratio. This report describes the design and protocol for the trial.

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.

Genotyping for CYP2C9 and VKORC1 alleles by a novel point of care assay with HyBeacon® probes

BACKGROUND Coumarin anticoagulants such as warfarin are used to treat and prevent thromboembolic events in patients. The required dosage is difficult to predict and the risk of over or under anticoagulation are dependent on several environmental and clinical factors, such as concurrent medication, diet, age and genotype for polymorphisms in two genes CYP2C9 and VKORC1. METHODS A novel fluorescent PCR genotyping assay using HyBeacon® probes, was developed to enable clinical staff to genotype the CYP2C9*2 and CYP2C9*3 alleles and the VKORC1 G-1639A polymorphism directly from unextracted blood samples. A prototype PCR instrument, Genie 1, suitable for point of care use was developed to carry out the assays. The panel of tests was validated by analysing blood samples from 156 individuals and comparing genotypes with data obtained using DNA samples from the same individuals. The accuracy of genotypes obtained with the Genie 1 was compared against results from well validated real time PCR and PCR-restriction fragment length polymorphism analysis. RESULTS Identical results were obtained for the newly developed HyBeacon® method and the validation method in all cases except for one where no result was obtained for the VKORC1 polymorphism on the Genie instrument. The samples used for validation represented all six possible *2 and *3 allele-related CYP2C9 genotypes and all three VKORC1 G-1639A genotypes. CONCLUSIONS We observed excellent accuracy for the newly developed method which can determine genotype in less than 2 h.

A systematic review of cost–effectiveness analyses of pharmacogenetic-guided dosing in treatment with coumarin derivatives

Anticoagulant therapy with coumarin derivatives is often sub- or supra-therapeutic, resulting in an increased risk of thromboembolic events or hemorrhage, respectively. Pharmacogenetic-guided dosing has been proposed as an effective way of reducing bleeding rates. Clinical trials to confirm the safety, efficacy and effectiveness of this strategy are ongoing, but in addition, it is also necessary to consider the cost-effectiveness of this strategy. This article describes the findings of a systematic review of published cost-effectiveness analyses of pharmacogenetic-guided dosing of coumarin derivatives. Similarities and differences in the approaches used were examined and the quality of the analyses was assessed. The results of the analyses are not sufficient to determine whether or not pharmacogenetic-guided dosing of coumarins is cost effective. More reliable cost-effectiveness estimates need to become available before it is possible to recommend whether or not this strategy should be applied in clinical practice.

Cost–effectiveness of pharmacogenetic-guided dosing of phenprocoumon in atrial fibrillation

AIM To investigate the cost-effectiveness of pharmacogenetic-guided phenprocoumon dosing versus standard anticoagulation care in Dutch patients with atrial fibrillation. MATERIALS & METHODS Using a decision-analytic Markov model, cost-effectiveness of pharmacogenetic-guided therapy versus standard care was estimated. RESULTS Compared with standard care, the pharmacogenetic-guided dosing strategy increased quality-adjusted life-years (QALYs) only very slightly and increased costs by €15. The incremental cost-effectiveness ratio was €2658 per QALY gained. In sensitivity analyses, the cost of genotyping had the largest influence on the cost-effectiveness ratio. In a probabilistic sensitivity analysis, the incremental costs of genotype-guided dosing were less than €20,000 per QALY gained in 75.6% of the simulations. CONCLUSION Pharmacogenetic-guided dosing of phenprocoumon has the potential to increase health slightly and may be able to achieve this in a cost-effective way. Owing to the many uncertainties it is too early to conclude whether or not patients starting phenprocoumon should be genotyped.

Validation of the acenocoumarol EU-PACT algorithms: similar performance in the Rotterdam Study cohort as in the original study

AIM To evaluate the performance of the European Pharmacogenetics of Anticoagulant Therapy (EU-PACT) acenocoumarol dose algorithms in an independent data set. The EU-PACT trial investigates the added value of pretreatment genotyping for use of warfarin, phenprocoumon and acenocoumarol. PATIENTS & METHODS External validation was performed in the Rotterdam Study cohort using information about 707 acenocoumarol users. R(2), which measures the strength of correlation between the predicted and observed acenocoumarol dose, mean absolute error and mean squared error were calculated to evaluate the performance of the original algorithm. RESULTS Validation resulted in a R(2) of 52.7 and 12.9% compared with an R(2) of 52.6 and 17.8% in the original study for the genotype-guided and nongenotype-guided dose algorithm, respectively. For the genotype-guided dose algorithm, the mean absolute error was 0.48 mg/day and the mean squared error was 0.38 (mg/day)(2). For the nongenotype-guided dose algorithm, the mean absolute error was 0.62 mg/day and the mean squared error was 0.63 (mg/day)(2). CONCLUSION The EU-PACT acenocoumarol algorithm performs just as accurately in this study as in the original study, which implies applicability in various populations.

Evaluation of the effect of statin use on the acenocoumarol and phenprocoumon maintenance dose.

Abstract Background: Statins and coumarins are prescribed in combination on a regular basis. Some case reports suggested that statins might affect the dose requirements of coumarins. The aim of the study was to investigate whether acenocoumarol and phenprocoumon maintenance doses are influenced by statin use. Methods: The Pre-EU-PACT database was used, which contains information on 471 acenocoumarol and 624 phenprocoumon users. The influence of individual statins on the acenocoumarol and phenprocoumon maintenance dose was investigated by comparing unadjusted and adjusted mean differences of the maintenance dose between statin and non-statin users. Results: Lower adjusted acenocoumarol dose requirements were observed for patients using atorvastatin, simvastatin, pravastatin, and rosuvastatin. These patients had a reduction in adjusted mean acenocoumarol maintenance dose of 0.11, 0.29, 0.38, and 0.69 mg/day, respectively, compared with a mean adjusted dose of 2.60 mg/day for the patients not using a statin. There was no significant effect of statin use on unadjusted and adjusted phenprocoumon maintenance dose (p=0.23 and p=0.35, respectively). Conclusions: Mean acenocoumarol maintenance dosages were decreased when acenocoumarol is co-administered with the different statins. Statin use does not affect phenprocoumon maintenance doses significantly.

Evaluation of the effect of genetic variations in GATA-4 on the phenprocoumon and acenocoumarol maintenance dose

AIM To investigate whether the phenprocoumon and acenocoumarol maintenance doses are influenced by genetic variations in GATA-4, a transcription factor of CYP2C9. PATIENTS & METHODS The influence of seven GATA-4 SNPs on the coumarin maintenance dose was investigated by performing an analysis of variance trend analysis, stratified for CYP2C9 genotypes. Results of the best-explaining SNP were validated in the Rotterdam Study cohort. RESULTS The largest dose differences were found for rs3735814 in patients using acenocoumarol and having the common allele for CYP2C9. The mean dosages decreased from 2.92 mg/day for the patients having the GATA-4 common alleles to 2.65 mg/day for the patients carrying one GATA-4 variant allele and to 2.37 mg/day for patients carrying two GATA-4 variant alleles (p = 0.004). Results could not be replicated in the validation cohort. For phenprocoumon, no significant effects were observed. CONCLUSION Genetic variation in GATA-4 does not seem relevant for clinical implementation.

The effect of omeprazole and esomeprazole on the maintenance dose of phenprocoumon

The response to vitamin K antagonists (VKAs) is determined by many different factors like age, weight, height, vitamin K intake and genetic polymorphisms [1]. The proton pump inhibitors (PPIs) omeprazole and esomeprazole may enhance the effect of VKAs by inhibition of the hepatic metabolism of coumarins [2]. Some isolated cases have been reported of clinically significant elevated INRs in patients concomitantly using omeprazole and phenprocoumon, a VKA frequently used in Europe [3]. Practical experience suggests an interaction between omeprazole or esomeprazole and phenprocoumon, but scientific evidence is still lacking. Van Schie et al. developed a dosing algorithm including age, gender, height, weight, CYP2C9 and VKORC1 genotypes and amiodarone use and a dosing algorithm without the genotypes to predict the phenprocoumon maintenance dose [4]. Given the possibility that omeprazole use affects the stable phenprocoumon maintenance dose, we examined whether information about its use would improve the predictive value of a dosing algorithm. Data from the pre-EU-PACT study were used to study the effect of omeprazole and esomeprazole on the stable phenprocoumon maintenance dose [4]. More details about this study can be found elsewhere [4]. The main outcome measure of the present study was the mean stable phenprocoumon maintenance dose in mg day−1 in the first stable period after initiation of phenprocoumon therapy. Only patients who reached a stable dose within 1 year were included in the analyses. Multiple linear regression analysis was used to develop a genotype-guided algorithm and a non-genotype-guided algorithm to estimate the square root of the weekly phenprocoumon maintenance dose. We included the same predictive variables used by van Schie et al. [4], but added an extra variable for omeprazole or esomeprazole use. A stable maintenance dose was reached within 1 year by 597 patients. Of these, 46 patients used omeprazole and 18 patients used esomeprazole. On average, non-users required 2.27 mg (SD 0.90) phenprocoumon day−1, significantly higher than the average dose seen in both omeprazole users (1.78 mg day−1, SD 0.73, 95% CI of the difference 0.22, 0.75) and esomeprazole users (1.88 mg day−1, SD 0.52, 95% CI of the difference 0.12, 0.66)). Since the phenprocoumon dose was not significantly different between omeprazole and esomeprazole users (95% CI of the difference −0.47, 0.28), we combined them into one group for inclusion in the algorithm. Five hundred and eighty-seven phenprocoumon users were included in the analysis of the non-genotype-guided algorithm and 559 for the genotype-guided algorithm. Omeprazole/esomeprazole use significantly influenced the phenprocoumon maintenance dose in the genotype-guided algorithm (P= 0.002) and the non-genotype-guided algorithm (P= 0.001) (Table 1). The genotype-guided algorithm was as follows: Table 1 Algorithms to predict stable phenprocoumon maintenance dose SQRT (maintenance dose (mg week−1) = 2.870–0.254 (if CYP2C9*1/*2) – 0.356 (if CYP2C9*1/*3) – 0.431 (if CYP2C9*2/*2) – 0.708 (if CYP2C9*2/*3) – 0.693 (if CYP2C9*3/*3) – 0.594 (if VCORC1 CT) – 1.371 (if VCORC1 TT) – 0.015 × Age (years) + 0.034 (if female) + 0.009 × Weight (kg) + 0.011 × Height (cm) – 0.315 (if amiodarone use) – 0.234 (if omeprazole/esomeprazole use). With this genotype-guided algorithm, 56.7% of dose variation could be explained, 0.8% more than in the study of van Schie et al. [4]. With our non-genotype-guided algorithm, the predictive value was 18.9%, 1.6% more than the algorithm of van Schie et al. [4]. The information obtained in this study could help physicians determine the right phenprocoumon dose for patients. If a patient is already using omeprazole or esomeprazole when phenprocoumon treatment is started, the dosing algorithm can be used to predict the required dose. If a patient starts using omeprazole or esomeprazole during phenprocoumon treatment the dose of phenprocoumon should be lowered. This could help prevent overanticoagulation and thereby reduce the risk of bleeding events when phenprocoumon and omeprazole or esomeprazole are used simultaneously. In this study we observed a lower phenprocoumon dose requirement in omeprazole and esomeprazole users and developed a dosing algorithm using this information. We only demonstrated the effect of omeprazole and esomeprazole. An interaction between phenprocoumon and other PPIs should be investigated in future research.