Barysheva V.O. ¹, Kremlev S.L. ², Ketova G.G. ¹, Likchacheva I.V. ¹, Astapenkova Y.V. ¹

¹Scientific-educational center ‘Clinical pharmacology’ of South Ural State Medical University, Chelyabinsk, Russia

² Clinic of South Ural State Medical University (Chelyabinsk, Russia)

THE RESULTS OF PHARMACOGENETIC TESTING HELD IN THE CLINIC OF SOUTH URAL STATE MEDICAL UNIVERSITY (CHELYABINSK, RUSSIA)

Backgrounds:

Pharmacogenetics-the study of interindividual differences in medication response as a result of genetic variations-has emerged as a potentially useful tool for individualizing medication regimens for patients. Genetic variations can affect drug disposition inseveral ways, from modifying receptor sensitivities to impacting drug metabolism. Over the last several years, the Food and Drug Administration has been steadily including pharmacogenetic information in drug labeling for several commonly prescribed drugs. Several organizations are attempting to provide evidence-based guidelines for widespread implementation and interpretation. (1)

Cardiovascular disease is a leading cause of death worldwide. Many pharmacologic therapies are available that aim to reduce the risk of cardiovascular disease but there is significant inter-individual variation in drug response, including both efficacy and toxicity. Pharmacogenetics aims to personalize medication choice and dosage to ensure that maximum clinical benefit is achieved whilst side effects are minimized. Over the past decade, our knowledge of pharmacogenetics in cardiovascular therapies has increased significantly. The anticoagulant warfarin represents the most advanced application of pharmacogenetics in cardiovascular medicine. Prospective randomized clinical trials are currently underway utilizing dosing algorithms that incorporate genetic polymorphisms in cytochrome P450 (CYP)2C9 and vitamin k epoxide reductase (VKORC1) to determine warfarin dosages. Polymorphisms in CYP2C9 and VKORC1 account for approximately 40 % of the variance in warfarin dose. There is currently significant controversy with regards to pharmacogenetic testing in anti-platelet therapy.(6)

Many anticipate that expanding knowledge of genetic variations associated with disease risk and medication response will revolutionize clinical medicine, making possible genetically based Personalized Medicine where health care can be tailored to individuals, based on their genome scans. Pharmacogenetics has received especially strong interest, with many pharmaceutical developers avidly working to identify genetic variations associated with individual differences in drug response. While clinical applications of emerging genetic knowledge are becoming increasingly available, genetic tests for drug selection are not as yet widely accessible, and many primary care clinicians are unprepared to interpret genetic information.(2)

Clopidogrel used in conjunction with aspirin has a central role in the treatment of patients with an acute coronary syndrome (ACS) and/or undergoing percutaneous coronary intervention (PCI). The pharmacokinetic and pharmacodynamic responses to this drug are highly variable leaving up to one third of patients with inadequate platelet inhibition or high on-treatment platelet reactivity (HPR), and subsequent increased ischemic cardiovascular events. Genetic variability in drug absorption and metabolism is a key factor responsible for the inefficient generation of the active drug metabolite. The two-step hepatic cytochrome P450 (CYP)-dependant oxidative metabolism of the prodrug appears to be of particular importance. Pharmacogenomic analyses have identified loss-of-function variant alleles of CYP 2C19 and specifically the 2C19*2 allele, to be the predominant genetic mediators of the antiplatelet effect of clopidogrel. Carriers were have been shown to have lower active metabolite levels of clopidogrel, higher platelet reactivity and associated poorer outcomes. (3)

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. (5)

Purpose:

To evaluate the results of pharmacogenetic testing held in the clinic of South Ural State Medical University (SUSMU).

Materials and methods:

Since 2013 in the clinic of SUSMU is held pharmacogenetic testing on such drugs as warfarin and clopidogrel. In this article we would like to describe the results of pharmacogenetic testing that were held in our clinic during this time.

Results:

Since 2013 in the clinic of SUSMU is held pharmacogenetic testing to determine the sensitivity to warfarin and resistance to clopidogrel.

The indications for carrying out pharmacogenetic testing on the drug warfarin are the initial dose of warfarin in patients with thrombosis (pulmonary embolism, deep vein thrombosis and other venous thrombosis, arterial thromboembolism, including embolic stroke) and in patients with high risk of thrombotic complications (constant form of atrial fibrillation, valve replacements, the postoperative period, including in orthopaedic practice).

Carriage of allelic variants of CYP2C9*2 and CYP2C9*3 and genotype AA from the polymorphic marker G3673A associated with low tailored dose of warfarin, instability of the anticoagulant effect, more frequent hemorrhages in its application. (4) In the laboratory of SUSMU the allelic variant CYP4F2 is also studied.

Certain formulas are used for dose selection. In the Russian patient population most optimal algorithm dosing of warfarin on the basis of the results of pharmacogenetic testing is the formula of Gage F.B. The initial dose of warfarin in accordance with the results of pharmacogenetic testing, can be calculated using the on-line calculator (http://www.warfarindosin.org) or with a help of the «Pharmacogenetics» module of the PharmSuite program.

First of all, private initial dose of warfarin is calculated, then the next dose of the drug is chosen by INR in accordance with the instruction for medical use. (4)

The results of pharmacogenetic testing on CYP2C9, VKORC1 and CYP4F2 can predict the range of fluctuations in daily maintenance dose of warfarin. Based on our research results, in 5% of cases allelic variant of CYP2C9*2 CT was detected, the variant VKORC1 GA was determined in 10% of cases, was met in 10% of cases allelic variant VKORC1 AA genotypes CYP4F2 CT, CYP4F2 TT were also detected in 5% of cases each. Thus, in 35% of cases we are faced with allelic variants that are associated with low tailored dose of warfarin, instability of the anticoagulant effect, more frequent bleeding, its use and require a certain dose selection, which was also held.

The indications for making pharmacogenetic testing on clopidogrel is forecasting the development of resistance clopidoglel and personalized selection of other antiplatelet agents in such cases as:

1. Patients with acute coronary syndrome recovery without ST segment elevation(unstable stenocardia or myocardial infarction without Q), including patients, who underwent stenting during percutaneous coronary intervention

2. Patients with acute coronary syndrome with ST-segment elevation (myocardial infarction) with medical treatment and the possibility of thrombolysis

3. Patients with other forms of CAD when the intolerance of acetylsalicylic acid takes place

4. Patients with ischemic stroke

5. Patients with diagnosed peripheral artery occlusive disease

When there takes places a «slow» allelic variants of the gene CYP2C19, encoding the main enzyme biotransformation of clopidogrel,it is noted a weak antiplatelet effect of clopidogrel in connection with the violation of its active metabolites in the liver, which leads to genetically determined resistance to this drug.

From all of the pharmacogenetic testings on clopidogrel - 100% of identified alleles CYP2C19 were not related to «slow» options. Thus, among the patients, aimed at pharmacogenetic study on the effectiveness of therapy with clopidogrel, the resistance was revealed.

Conclusions:

Since 2013 in the clinic of South Ural State Medical University is held pharmacogenetic testing on drugs warfarin and clopidogrel.

In the result of evaluation of the tests we can say that in 35% of cases were detected allelic variants in which takes place the instability of anticoagulant effect, more frequently bleeding in the application and required a certain selection of the dose that is also conducted by clinical pharmacologists of the clinic of South Ural State Medical University

From all of the pharmacogenetic testing that were held on clopidogrel - 100% of identified alleles CYP2C19 were not related to «slow» options. Thus, among the patients, aimed at pharmacogenetic study on the effectiveness of therapy by clopidogrel, resistance was not revealed.

Literature:

1. Beier MT Pharmacogenetics: has the time come for pharmacists to embrace and implement the science?/ Beier MT, Panchapagesan M, Carman LE.// Consult Pharm.– 2013.– No28(11)

2. Hunt LM.Pharmacogenetics in primary care: the promise of personalized medicine and the reality of racial profiling/ Hunt LM, Kreiner MJ.// Cult Med Psychiatry.– 2013.– No37(1)

3. O'Connor SA. Pharmacogenetics of clopidogrel./ O'Connor SA, Hulot JS, Silvain J, Cayla G, Montalescot G, Collet JP..// Curr Pharm Des.– 2012

4. Sychev DA. Algorithms of dosing warfarin, based on the results of pharmacogenetic testing: a real opportunity to optimize the pharmacotherapy / D.A. Sychev, I.M. Antonov, S.V. Zagrebin, N.A. Hasanov, V.G. Kukes// Rational pharmacotherapy in cardiology.-2007/-№2

5. Verhoef TI. Pharmacogenetic-guided dosing of coumarin anticoagulants: algorithms for warfarin, acenocoumarol and phenprocoumon../ Verhoef TI, Redekop WK, Daly AK, van Schie RM, de Boer A, Maitland-van der Zee AH..// Br J Clin Pharmaco.– 2013

6. Yip VL. Expanding role of pharmacogenomics in the management of cardiovascular disorders./ Yip VL, Pirmohamed M.// Am J Cardiovasc Drugs.– 2013.– No13(3)