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Pharmacogenomics is the study of how genetic variation between individuals´ influences responses to drugs. This new field combines the science of how drugs work, called pharmacology, with the science of the human genome, called genomics.

It is important to understand that all the individuals are genetically unique and that is also the reason why response to drug metabolites is unique to each individual. Pharmacogenomics helps to determine how individuals´ genes and their variants impact drug absorption, metabolism and activity. While one treatment approach may work well for one individual, the same approach may not be effective or may cause toxic effects even at a lower dose for another. [1, 2]

Our understanding of the variability of drug response has advanced markedly in the last decades. Many relevant polymorphisms have been identified and variations in metabolic rates can often be tested using pharmacogenomics [3]. For example, the genetic polymorphism of CYP2D6 and CYP2C19 enzymes cause variance in the metabolic rates of several drugs. Patients can be divided into four different groups based on the genetically determined metabolic rates of these enzymes: ultrarapid, extensive, intermediate and poor metabolizers. For example, codein used as a cough medicine and pain killer, is metabolized by CYP2D6 enzyme in the liver and part of the codein transforms to morphine. For poor CYP2D6 metabolizers, codein is ineffective, while ultrarapid mobilizers might have serious side effects or even life-threatening toxic effects [4].

Pharmacogenetic testing aims to guide clinicians to prescribe the right drug with the right dose to the right patient, leading to better efficacy, fewer adverse drug reactions, and a better cost-benefit ratio of the drug treatments [2]. However, pharmacogenomic testing has not yet been widely adopted into the clinic. In Finland, the reasons behind the slow adoption of the pharmacogenomic testing relate to poor availability, high price and lack of knowledge concerning the usability of the pharmacogenomic testing [4]. One major challenge for the clinical uptake of pharmacogenomic testing is also the difficulty to translate genetic laboratory test results into practical prescription guidelines of the affected drugs [3].

Several co-operation bodies have been established to facilitate the use of pharmacogenetic tests for patient care, e.g. European Pharmacogenetics Implementation Consortium (EU-PIC) and Clinical Pharmacogenetics Implementation Consortium (CPIC) working under National Institutes of Health. CPIC’s goal is to address the barrier to clinical implementation of pharmacogenetic tests by creating, curating, and posting freely available, peer-reviewed, evidence-based, updatable, and detailed gene/drug clinical practice guidelines. [5, 6]

References:

1. Wang L, McLeod H, Weinshilboum RM. Genomics and drug response. N Engl J Med, 364:1144-1153, 2011. 2. Kitzmiller JP, Groen DK, Phelps MA, Sadee W. Pharmacogenomic testing: relevance in medical practice: why drugs work in some patients but not in others. Cleve Clin J Med, 78(4):243-257, 2011.

3. Relling MV and Evans WE. Pharmacogenomics in the clinic. Nature, 526 (7573):343-350, 2015.

4. Heliste J, Elenius K, Niemi M, Elenius V. Farmakogenetiikka saapuu klinikkaan. Duodecium, 132:1561-1568, 2016. 5. European Pharmacogenetics Implementation Consortium (EU-PIC) Website: http://www.eu-pic.net/ 6. Clinical Pharmacogenetics Implementation Consortium (CPIC) Webite: https://cpicpgx.org/

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