2-oxo-clopidogrel, an intermediate and pharmacologically inactive metabolite, is formed by cytochrome P450, which is then further converted into the pharmacologically active metabolite (clopi-H4) by the same pathway. In vitro enzyme kinetics studies have revealed that CYP1A2 (35.8%), CYP2B6 (19.4%) and CYP2C19 (44.9%) contribute to the formation of 2-oxo-clopidogrel, whereas CYP2B6 (32.9%), CYP2C9 (6.79%), CYP2C19 (20.6%) and CYP3A4 (39.8%) contribute to the formation of the active metabolite \cite{Jiang_2015}.
Epidemiology
The CYP2C19*2 polymorphism, is also known as poor metabolizer because it has been related with a decreased enzymatic activity function \cite{Bergmeijer_2012}, specially in those who have the presence of the SNP in both alleles, that strongly suggest a reduction in clopidogrel matabolism leading to a decrease in its antiplatelet effect. According to a study performed with 51 mexican patients, 9 (17%) of them were found to carry the CYP2C19*2 polymorphism  \cite{Viveros_2016}. Of these, seven (13.7%) were heterozygotes and two (3.9%) were homozygous. The remaining 42 patients had the wild-type genotype. This results showed that 3.9% of patients had the homozygous genotype, wich is higher thant the previously reported frequency of 0-1.45% in the Mexican Mestizo groups \cite{Viveros_2016}.