Dosing algorithms for vitamin K antagonists across VKORC1 and CYP2C9 genotypes.

Essentials Prospective studies of pharmacogenetic-guided (PG) coumarin dosing produced varying results. EU-PACT acenocoumarol and phenprocoumon trials compared PG and non-PG dosing algorithms. Sub-analysis of EU-PACT identified differences between trial arms across VKORC1-CYP2C9 groups. Adjustment of the PG algorithm might lead to a higher benefit of genotyping. SUMMARY: Background The multicenter, single-blind, randomized EU-PACT trial compared the safety and efficacy of genotype-guided and non-genetic dosing algorithms for acenocoumarol and phenprocoumon in patients with atrial fibrillation or deep vein thrombosis. The trial showed no differences in the primary outcome between the two dosing strategies. Objectives To explore possible reasons for the lack of differences between trial arms by performing a secondary analysis of EU-PACT data in order to evaluate the performance of both dosing algorithms across VKORC1-CYP2C9 genetic subgroups. Patients/Methods Anticoagulation control measured according to an International Normalized Ratio (INR) below (INR of < 2), within (INR of 2-3) and above (INR of > 3) the therapeutic range was compared across VKORC1-CYP2C9 subgroups. Owing to a low number of patients in each subgroup, trials for acenocoumarol and phenprocoumon were combined for analysis. Results Four weeks after therapy initiation, genotype-guided dosing increased the mean percentage of time in the therapeutic INR range (PTIR) in the VKORC1 GG-CYP2C9*1*1 subgroup as compared with the non-genetic dosing (difference of 14.68%, 95% confidence interval [CI] 5.38-23.98). For the VKORC1 AA-CYP2C9*1*1 subgroup, there was a higher risk of under-anticoagulation with the genotype-guided algorithm (difference of 19.9%; 95% CI 11.6-28.2). Twelve weeks after therapy initiation, no statistically significant differences in anticoagulation control between trial arms were noted across the VKORC1-CYP2C9 genetic subgroups. Conclusions EU-PACT genetic-guided dose initiation algorithms for acenocoumarol and phenprocoumon could have predicted the dose overcautiously in the VKORC1 AA-CYP2C9*1*1 subgroup. Adjustment of the genotype-guided algorithm could lead to a higher benefit of genotyping.

Age-stratified outcome of a genotype-guided dosing algorithm for acenocoumarol and phenprocoumon.

Essentials The EU-PACT trial was used to investigate age on the interaction between coumarins and genotype. The results support the use of genotype-guided dosing for phenprocoumon in patients < 75 years. For patients ≥ 75 years the phenprocoumon algorithm should be revised and further tested. No influence of comorbidities and co-current drug use was found that could explain the differences. SUMMARY: Background Age seemed to affect the interaction between coumarins and genotype in the acenocoumarol and phenprocoumon arm of the European Pharmacogenetics of Anticoagulant Therapy (EU-PACT) trial. Objectives To investigate the effect of genotype-guided dosing stratified by age and the potential factors causing a difference. Patients/Methods Data from the acenocoumarol/phenprocoumon arm of the EU-PACT trial were used. The percentages of time below the therapeutic range, time above the therapeutic range and time in the therapeutic range (TTR) during the initial 12 weeks of therapy were compared between the genotype-guided group and the control group among younger (< 75 years) and older (≥ 75 years) patients by the use of independent t-tests, and adjusted for sex, height, weight and co-medications by the use of linear regression. Results Among younger phenprocoumon users, TTR during the first 12 weeks in the genotype-guided group (n = 55) was 9.5% (95% confidence interval [CI] 1.3 to 17.8) higher than in the control group (n = 63), with a remarkably lower percentage of time above this range (difference: - 9.6%, 95% CI - 19.0 to - 0.2) and a similar time below this range. Older patients dosed by the genotype-guided algorithm (n = 24) spent more time above the range (difference: 27.5%, 95% CI 12.9 to 42.0). For acenocoumarol users, there were no significant differences between the genotype-guided and control groups for most outcomes, except for a lower percentage of time below the range among older patients. Conclusions The genotype-guided algorithm for phenprocoumon in the EU-PACT trial benefitted younger patients more, but for older patients the algorithm needs to be revised and tested in further research.

Cost-effectiveness of pharmacogenetic-guided dosing of warfarin in the United Kingdom and Sweden.

We aimed to assess the cost-effectiveness of pharmacogenetic-guided dosing of warfarin in patients with atrial fibrillation (AF) in the United Kingdom and Sweden. Data from EU-PACT, a randomized controlled trial in newly diagnosed AF patients, were used to model the incremental costs per quality-adjusted life-year (QALY) gained by pharmacogenetic-guided warfarin dosing versus standard treatment over a lifetime horizon. Incremental lifetime costs were £26 and 382 Swedish kronor (SEK) and incremental QALYs were 0.0039 and 0.0015 in the United Kingdom and Sweden, respectively. The corresponding incremental cost-effectiveness ratios (ICERs) were £6 702 and 253 848 SEK per QALY gained. The ICER was below the willingness-to-pay threshold of £20 000 per QALY gained in 93% of the simulations in the United Kingdom and below 500 000 SEK in 67% of the simulations in Sweden. Our data suggest that pharmacogenetic-guided dosing of warfarin is a cost-effective strategy to improve outcomes of patients with AF treated with warfarin in the United Kingdom and in Sweden.

Patients benefit from genetics-guided coumarin anticoagulant therapy.

Observational studies have overwhelmingly shown that variants in the genes CYP2C9 and VKORC1 are significant determinants of individual dose of coumarin anticoagulants needed to maintain a therapeutic international normalized ratio (INR).(1) Until recently, however, few randomized clinical trials had been performed relating to the use of genetic data to predict dosing. Three sucsh clinical trials have now reported their findings.

An evaluation of gene-gene interaction between the CYP2C9 and VKORC1 genotypes affecting the anticoagulant effect of phenprocoumon and acenocoumarol.

BACKGROUND: Previous studies have provided contradictory results regarding the interaction between the CYP2C9 and VKORC1 genotypes affecting various outcome measures. OBJECTIVES: We aimed to provide a definite answer regarding the question whether there exists a gene-gene interaction between the CYP2C9 and VKORC1 genotypes affecting the anticoagulant effect of phenprocoumon and acenocoumarol. PATIENTS/METHODS: The EU-PACT cohort dataset, which contains data on 624 phenprocoumon and 471 acenocoumarol patients, was used. Patient characteristics, pharmacogenetic data, International Normalized Ratios (INRs) and dosages were available. We investigated whether there was an interaction between the CYP2C9 and VKORC1 genotypes affecting the maintenance dose, time to severe over-anticoagulation and time to achieve stability during the first 180 days of phenprocoumon and acenocoumarol therapy, in addition to the effect of the separate genotypes. The interaction effect was investigated by adding the product term of the CYP2C9 and VKORC1 genotype classes for four different commonly used CYP2C9 classifications to the linear regression model - for the outcome measure maintenance dose - or to the Cox regression models - for the outcome measures time to severe over-anticoagulation and time to achieve stability. RESULTS: No significant interactions - all P-values above 0.23 for phenprocoumon and 0.30 for acenocoumarol - were observed for all outcome measures. CONCLUSIONS: There are no interactions between the CYP2C9 and VKORC1 genotypes affecting the maintenance dose, time to severe over-anticoagulation and time to achieve stability for phenprocoumon and acenocoumarol.

Long-term anticoagulant effects of the CYP2C9 and VKORC1 genotypes in acenocoumarol users.

BACKGROUND: The required acenocoumarol dose and the risk of underanticoagulation and overanticoagulation are associated with the CYP2C9 and VKORC1 genotypes. However, the duration of the effects of these genes on anticoagulation is not yet known. OBJECTIVES: In the present study, the effects of these polymorphisms on the risk of underanticoagulation and overanticoagulation over time after the start of acenocoumarol were investigated. PATIENTS/METHODS: In three cohorts, we analyzed the relationship between the CYP2C9 and VKORC1 genotypes and the incidence of subtherapeutic or supratherapeutic International Normalized Ratio (INR) values (< 2 and > 3.5) or severe overanticoagulation (INR > 6) for different time periods after treatment initiation. RESULTS: Patients with polymorphisms in CYP2C9 and VKORC1 had a higher risk of overanticoagulation (up to 74%) and a lower risk of underanticoagulation (down to 45%) in the first month of treatment with acenocoumarol, but this effect diminished after 1-6 months. CONCLUSIONS: Knowledge of the patient's genotype therefore might assist physicians to adjust doses in the first month(s) of therapy.