Extreme sensitivity to acenocoumarol therapy in patient with both VKORC.-1639 A/A and CYP2C9*1/*3 genotypes

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

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

Acenocoumarol Pharmacogenetic Dosing Algorithms and Their Application in Two Bulgarian Patients with Low Anticoagulant Requirements

BACKGROUND

The anticoagulant therapy with acenocoumarol is generally associated with a high risk of bleeding and thromboembolic events.

PURPOSE

We applied eight already existing acenocoumarol dosing algorithms to Bulgarian patients with low acenocoumarol dose requirements and investigated which of these algorithms would predict most precisely the dose anticoagulant.

MATERIALS AND METHODS

Two patients with Bulgarian origin were referred to the outpatient clinical laboratory of "St. Ekaterina" University Hospital for Cardiovascular Surgery and Cardiology, Sofia, Bulgaria. After obtaining written informed consent, both patients were genotyped for polymorphisms in genes for Cytochrome P450 2C9 (CYP2C9), Vitamin K epoxide reductase (VKORC1), Apolipoprotein E (APOE), and Cytochrome P450 4F2 (CYP4F2).

RESULTS

All applied acenocoumarol dosing algorithms predicted relatively similar doses of coumarin anticoagulant in both patients. However, van Schie et al.'s algorithm allowed more accurate calculation of the optimal dose in our patients with extremely low acenocoumarol requirements. Genotyping of selected polymorphic variants in CYP2C9 and VKORC1 showed that both patients were compound heterozygotes for CYP2C9 (CYP2C9*2/*3) and homozygotes for both variants in VKORC1 (VKORC1 1173 T/T, and VKORC1-1639 A/A). This combination of genotypes suggested high sensitivity to acenocoumarol leading to the low anticoagulant dose requirements (0.25 and 1 mg/day, respectively) needed to reach the target International Normalized Ratio of 2.5-3.5.

CONCLUSIONS

The genotyping of polymorphic variants in VKORC1 and CYP2C9, together with clinical and demographic parameters, can serve for more precise definition of the individual starting and maintenance doses of coumarin derivatives in each patient.

Estimation and validation of acenocoumarol dosing algorithms in Bulgarian patients with cardiovascular diseases

Aim & Methods: A total of 169 Bulgarian patients were genotyped for CYP2C9*2,*3, VKORC1-1639G>A and VKORC11173C>T. The effect of genetic and nongenetic factors on acenocoumarol dose variability was tested in a derivation cohort of patients and the obtained algorithm was validated in a test cohort.

RESULTS & DISCUSSION

It was found that VKORC-1639G>A (25.5%), CYP2C9*2 (7.8%), CYP2C9*3 (6.1%), age (13.6%) and diagnosis (6.0%) significantly affected acenocoumarol dose variability in the derivation cohort. These factors with additional factors, such as sex (0.1%, p = 0.76), weight (2.6%, p = 0.14) and amiodarone use (3.0%, p = 0.059) accounted for 46.5% and 23.0% of the dose variability for genetic and clinical models, respectively.

CONCLUSION

Based on the results of this investigation, validated clinical and pharmacogenetic algorithms for the prediction of a stable anticoagulant dose were developed, specifically designed for the Bulgarian population.