Optimizing clopidogrel dose response: a new clinical algorithm comprising CYP2C19 pharmacogenetics and drug interactions

Yolande B Saab,1 Rony Zeenny,2 Wijdan H Ramadan2 1School of Pharmacy, Pharmaceutical Sciences Department, 2School of Pharmacy, Pharmacy Practice Department, Lebanese American University, Byblos, Lebanon Purpose: Response to clopidogrel varies widely with nonresponse rates ranging from 4% to 30%. A reduced function of the gene variant of the CYP2C19 has been associated with lower drug metabolite levels, and hence diminished platelet inhibition. Drugs that alter CYP2C19 activity may also mimic genetic variants. The aim of the study is to investigate the cumulative effect of CYP2C19 gene polymorphisms and drug interactions that affects clopidogrel dosing, and apply it into a new clinical-pharmacogenetic algorithm that can be used by clinicians in optimizing clopidogrel-based treatment. Method: Clopidogrel dose optimization was analyzed based on two main parameters that affect clopidogrel metabolite area under the curve: different CYP2C19 genotypes and concomitant drug intake. Clopidogrel adjusted dose was computed based on area under the curve ratios for different CYP2C19 genotypes when a drug interacting with CYP2C19 is added to clopidogrel treatment. A clinical-pharmacogenetic algorithm was developed based on whether clopidogrel shows 1) expected effect as per indication, 2) little or no effect, or 3) clinical features that patients experience and fit with clopidogrel adverse drug reactions. Results: The study results show that all patients under clopidogrel treatment, whose genotypes are different from *1*1, and concomitantly taking other drugs metabolized by CYP2C19 require clopidogrel dose adjustment. To get a therapeutic effect and avoid adverse drug reactions, therapeutic dose of 75 mg clopidogrel, for example, should be lowered to 6 mg or increased to 215 mg in patients with different genotypes. Conclusion: The implementation of clopidogrel new algorithm has the potential to maximize the benefit of clopidogrel pharmacological therapy. Clinicians would be able to personalize treatment to enhance efficacy and limit toxicity. Keywords: pharmacogenetics, genotype, genetic testing, individualized therap

Buccal cells submitted to three different storage conditions before DNA extraction

This study evaluated quantitatively and qualitatively the effect of the storage time of samples before the application of the cell lysis solution (CLS) for extracting DNA from buccal cells (BC). BC from the upper and lower gutter region were collected from 5 volunteers using special cytobrushes (Gentra), totaling 3 collections for each individual. In the control group (n=10), CLS was applied soon after BC collection. In the other two groups, samples were stored at room temperature (n=10) or at 4°C (n=10). After CLS application, DNA was extracted according to the manufacturer's instructions (Puregene DNA Buccal Cell Kit; Gentra Systems, Inc.). The DNA obtained was evaluated by two calibrated blind examiners using spectrophotometry and analysis of DNA bands (0.8% agarose gel electrophoresis). The obtained data were submitted to one-way ANOVA. The means and standard deviations for DNA extracted under immediate, room temperature and cooling temperature conditions were 3.5 ± 0.7, 3.0 ± 0.6 and 4.1 ± 1.8 µg, respectively (p=0.385). No significant differences were found in relation to the amount of DNA for the different storage conditions. However, in the visual analysis of the DNA bands, no trace of DNA degradation was detected when CSL was applied soon after DNA collection, while DNA bands with degradation could be observed in the other groups. Within the limitations of the study, it may be concluded that CLS should be applied soon after DNA collection in order to obtain high-quality DNA from BC