Background-Well characterized genes affecting warfarin metabolism (CYP2C9) and sensitivity (VKORC1) explain one-third of the variability in therapeutic dose before the International Normalized Ratio (INR) is measured.

Clinical implementation of pharmacogenomics (PGx) leads to personalized medicine, which improves the efficacy, safety, and cost-effectiveness of treatments. Although PGx-based research has been conducted for more than a decade, several barriers have slowed down its widespread implementation in clinical practice. Globally, there is an imbalance in programs and solutions required to empower the clinical implementation of PGx between countries. Therefore, we aimed to review these issues comprehensively, determine the major barriers, and find the best solutions. Through an extensive review of ongoing clinical implementation programs, scientific, educational, ethical, legal, and social issues, information technology, and reimbursement were identified as the key barriers. The pace of global implementation of genomic medicine coincided with the resource limitations of each country. The key solutions identified for the earlier mentioned barriers are as follows: building of secure and suitable information technology infrastructure with integrated clinical decision support systems along with increasing PGx evidence, more regulations, reimbursement strategies for stakeholder's acceptance, incorporation of PGx education in all institutions and clinics, and PGx promotion to all health care professionals and patients. In conclusion, this review will be helpful for the better understanding of common barriers and solutions pertaining to the clinical application of PGx.

The early detection of potential drug-drug interactions is an important issue of drug discovery that has led to the development of high-throughput screening (HTS) methods for potential drug interactions. We developed a HTS method for potential interactions of inhibitory drugs for nine human P450 enzymes using cocktail incubation and tandem mass spectrometry in vitro. This new method involves incubation of two cocktail doses and single cassette analysis. The two cocktail doses in vitro were developed to minimize solvent effects and mutual drug interactions among substrates: cocktail A was composed of phenacetin for CYP1A2, coumarin for CYP2A6, paclitaxel for CYP2C8, S-mephenytoin for CYP2C19, dextromethorphan for CYP2D6, and midazolam for CYP3A4; and cocktail B was composed of three substrates including bupropion for CYP2B6, tolbutamide for CYP2C9, and chlorzoxazone for CYP2E1. In the incubation study of these cocktails, the reaction mixtures were pooled and simultaneously analyzed using liquid chromatography/tandem mass spectrometry employing a fast gradient. The method was validated by comparing the inhibition data obtained from the incubation of each individual probe substrate alone with data from the new method. The IC50 value of each inhibitor in the cocktail agreed well with that of the individual probe drug as well as with values previously reported in the literature. As a HTS method for potential interactions of the inhibition of these nine P450 enzymes, this new method will be useful in the drug discovery process and for the mechanistic understanding of drug interactions.

ABSTRACT:Ebastine undergoes extensive metabolism to form desalkylebastine and hydroxyebastine. Hydroxyebastine is subsequently metabolized to carebastine. Although CYP3A4 and CYP2J2 have been implicated in ebastine N-dealkylation and hydroxylation, the enzyme catalyzing the subsequent metabolic steps (conversion of hydroxyebastine to desalkylebastine and carebastine) have not been identified. Therefore, we used human liver microsomes (HLMs) and expressed cytochromes P450 (P450s) to characterize the metabolism of ebastine and that of its metabolites, hydroxyebastine and carebastine. In HLMs, ebastine was metabolized to desalkyl-, hydroxy-, and carebastine; hydroxyebastine to desalkyland carebastine; and carebastine to desalkylebastine. Of the 11 cDNA-expressed P450s, CYP3A4 was the main enzyme catalyzing the N-dealkylation of ebastine, hydroxyebastine, and carebastine to desalkylebastine [intrinsic clearance (CL int ) ‫؍‬ 0.44, 1.05, and 0.16 l/min/pmol P450, respectively]. Ebastine and hydroxyebastine were also dealkylated to desalkylebastine to some extent by CYP3A5. Ebastine hydroxylation to hydroxyebastine is mainly mediated by CYP2J2 (0.45 l/min/pmol P450; 22.5-and 7.5-fold higher than that for CYP3A4 and CYP3A5, respectively), whereas CYP2J2 and CYP3A4 contributed to the formation of carebastine from hydroxyebastine. These findings were supported by chemical inhibition and kinetic analysis studies in human liver microsomes. The CL int of hydroxyebastine was much higher than that of ebastine and carebastine, and carebastine was metabolically more stable than ebastine and hydroxyebastine. In conclusion, our data for the first time, to our knowledge, suggest that both CYP2J2 and CYP3A play important roles in ebastine sequential metabolism: dealkylation of ebastine and its metabolites is mainly catalyzed by CYP3A4, whereas the hydroxylation reactions are preferentially catalyzed by CYP2J2. The present data will be very useful to understand the pharmacokinetics and drug interaction of ebastine in vivo.Ebastine, a potent and selective histamine H 1 -receptor antagonist, belongs to a second generation of nonsedating antihistamines but with negligible anticholinergic and antiserotonergic properties (Llupia et al., 2003). Ebastine undergoes extensively sequential metabolism in the liver (Hashizume et al., 1998(Hashizume et al., , 2001). The major primary metabolites identified in humans are hydroxy-and desalkylebastine, and hydroxyebastine is further metabolized to carebastine. In vitro studies indicate that the formation of desalkyl-and hydroxyebastine from ebastine is catalyzed by CYP3A4 and CYP2J2, respectively (Hashizume et al., 2002). The specific hepatic cytochrome P450 (P450) enzymes involved in hydroxy-and carebastine metabolism have not been identified so far, despite some information which could be obtained from the previously published pharmacokinetics of ebastine. After oral administration to experimental animals and humans, ebastine is almost completely metabolized to the pharmacologically active princi...