Cytochrome P450 2C19 enzyme, Cytochrome P450 2C9 enzyme, and Cytochrome P450 2D6 enzyme allelic variants and its possible effect on drug metabolism A retrospective study

The objective of the present study was to assess the allelic variations of Cytochrome P450 (CYP) enzymes Cytochrome P450 2C19 (CYP2C19), Cytochrome P450 2C9 (CYP2C9), and Cytochrome P450 2D6 (CYP2D6) as they play a major role in drug metabolism. The interindividual genetic variabilities of these enzymes can account for different responsiveness as well as concentration fluctuations for a particular drug. During the period of 2017 to 2018 a total of 54 patients have received pharmacogenetic testing at the Department of Genetics and Molecular Medicine at Kaunas Clinics. According to the genotype-metabolic phenotypes of CYP2C19, CYP2D6, CYP2C9 enzymes patients were classified according to the guidelines by Clinical Pharmacogenetics Implementation Consortium (CPIC): normal metabolizers (NMs), intermediate metabolizers (IMs), rapid metabolizers (RMs), ultrarapid metabolizers (UMs), and poor metabolizers (PMs). CYP2C19 enzyme allelic distribution: 18 patients (33.33%) with *1/*1 genotype were NMs; 14 patients (25.93%) with *1/*2; *2/*17 genotypes were classified as IMs; 15 patients (27.78%) possessed *1/*17 genotype and were RMs; 4 patients (7.4%) had *17/*17 genotype with increased enzyme activity compared with RMs, were classified as UMs; 3 patients (5.56%) had *2/*2 genotype and were marked as PMs. CYP2D6 enzyme allelic distribution: 26 patients (48.148%) contained *1/*1,*2/*2,*1/*2,*1/*41,*2/*41 genotypes with normal enzymatic function so were accounted as NMs; 21 patients (38.89%) with *1/*5, *2/*4, *10/*41, *1/*4, *1/*3, *2/*5, *2/*4, *2/*6 genotypes were accounted as IMs; 2 patients (3.7%) possessed *2XN genotype and were accounted as UMs and 5 patients (9.26%) possessed *4/*5,*4/*10,*4/*9,*4/*41 genotypes and had non-functional enzymatic activity so were accounted as PMs; CYP2C9 enzyme allelic distribution: 44 patients (81.48%) with*1/*1 genotype were NMs; 10 patients (18.52%) with *1/*2;*1/*3 genotypes were IMs. The results of our study indicate that deviations from the normal enzymatic activity is common amongst Lithuanian people and combinatory genotyping of CYP2D6, CYP2C9, and CYP2C19 has to be promoted as an advanced method because of most commonly prescribed medicines like analgesics, antihypertensive, antidepressants are metabolized by multiple pathways involving enzymes in the CYP450 family.