CYP2C19 polymorphism in relation to the pharmacotherapy optimization of commonly used drugs.

: The CYP2C19 isoenzyme plays an important role in the efficacy and safe use of many drugs. The aim of this review is to demonstrate how mutations influence everyday patient treatment, leading to adverse drug reactions or therapy failure in many common diseases. : A PubMed literature search was performed on clinical publications evaluating the impact of on pharmacotherapy outcome. Main fields of medicine with strong outcome dependency on the genotype were selected. We also focused on clinical recommendations for the use of drugs referring to polymorphism. The fields of medicine where clinical outcome particularly depends on polymorphism are gastroenterology, cardiology, psychiatry, mycology and oncology. CYP2C19 is involved in proton pump inhibitors metabolism, thus it can influence reflux therapy, ulcer prevention and eradication treatment. The CYP2C19 enzyme plays also a vital role in the two bioactivation steps of clopidogrel leading to lower ( carriers) or higher ( carriers) risk of major adverse cardiovascular events. It affects the antidepressant treatment and methadone replacement therapy as well as voriconazole prophylaxis. The presence of a *2 allele is associated with longer relapse-free time or better survival, and the *17 allele with more favorable outcomes in breast cancer patients treated with tamoxifen. : Knowledge of the polymorphism could positively affect individual treatment and lead to better patient outcomes in many cases. The introduction of pharmacogenetic testing into medical practice would be a good way to minimize negative outcomes of therapy, and to reduce unnecessary medical costs.