CYP2C19- and CYP3A4-Dependent Omeprazole Metabolism in West Mexicans

Identification and kinetics of microsomal and recombinant equine liver cytochrome P450 enzymes responsible for in vitro metabolism of omeprazole

In humans, omeprazole is metabolised by cytochrome P450 (CYP450) CYP2C19 and CYP3A4 with differences in CYP2C19 genotypes leading to variable response to therapy. Despite a wide use of omeprazole in horses with evidence of variable therapeutic efficiency, information regarding enzymatic metabolism is not currently available. This study aims to describe the in vitro kinetics of omeprazole metabolism and determine which enzyme(s) are responsible for omeprazole metabolism in horses. Omeprazole (0-800 uM) was incubated with liver microsomes and a panel of equine recombinant CYP450s (eq-rCYP). Metabolite concentrations were quantified by LC-MS and the kinetics of metabolites' formation were calculated by non-linear regression analysis. The in vitro liver microsomes formed three metabolites (5-hydroxy-omeprazole, 5-O-desmethyl-omeprazole and omeprazole-sulfone). The 5-O-desmesthyl-omeprazole formation was best fitted to a two enzyme Michaelis-Menten (MM) model with the high affinity site Clint double that of the low affinity site. For 5-hydroxy-omeprazole the best fit was to a 1 enzyme MM model with a Clint higher than for 5-O-desmesthyl-omeprazole (0.12 vs 0.09 pmol/min/pmol P450). The formation of omeprazole-sulfone was negligible. Recombinant CYP3A89 and CYP3A97 produced substantial amounts of 5-hydroxy-omeprazole (1551.72 ng/mL and 1665.33 ng/mL, respectively), while 5-O-desmethyl-omeprazole and omeprazole-sulfone were formed to a much lesser extent by multiple eq-rCYP from the CYP2C and CYP3A family. In vitro metabolism of omeprazole in horses is different to that in humans, with major metabolites produced by the CYP3A family. The current study provides the basis for further investigations of CYP450 single nucleotide polymorphisms that could affect omeprazole metabolism and therapeutic efficacy.

Nifedipine Does Not Alter the Pharmacokinetics of Venlafaxine Enantiomers in Healthy Subjects Phenotyped for CYP2D6, CYP2C19, and CYP3A

Venlafaxine (VEN) is a P-glycoprotein (P-gp) substrate, and nifedipine has been described by in vitro and experimental studies as a P-gp inhibitor. The present study aimed to investigate whether nifedipine alters the kinetic disposition of VEN enantiomers and their metabolites in healthy subjects. A crossover study was conducted in 10 healthy subjects phenotyped as extensive metabolizers for cytochrome P450 (CYP) 2D6, CYP2C19, and CYP3A. In phase 1, the subjects received a single oral dose of 150 mg racemic VEN, and in phase 2, a single oral dose of 40 mg nifedipine was administered with the VEN treatment. Plasma concentrations of VEN enantiomers and their metabolites O-desmethylvenlafaxine and N, O- didesmethylvenlafaxine (ODV and DDV, respectively) were evaluated by liquid chromatography with tandem mass spectrometry up to 72 hours after drug administration. Phase 2 was compared with phase 1 using the 90% confidence interval (CI) of the ratio of geometric means for C_max and area under the curve (AUC). AUC enantiomeric ratios S-(+)/R-(-) were evaluated within each and between phases using the Wilcoxon test (P ≤ .05). The kinetic disposition of VEN was enantioselective (phase 1) with VEN S-(+)/R-(-) AUC ratio median of 2.83 (AUC_0-∞ , 526 vs 195 ng·h/mL). However, AUC median did not differ between enantiomers for the metabolites ODV (1971 vs 2226 ng·h/mL) and DDV (199 vs 151 ng·h/mL). The 90%CI of the ratio of geometric means showed that the phases are bioequivalent. A single oral dose of 40 mg nifedipine did not alter VEN enantiomer pharmacokinetics in healthy subjects.

Interethnic variability of pharmacogenetic biomarkers in Mexican healthy volunteers: a report from the RIBEF (Ibero-American Network of Pharmacogenetics and Pharmacogenomics)

Mexico presents a complex population diversity integrated by Mexican indigenous (MI) (7% of Mexico's population) and Mexican mestizos (MMs). This composition highlights the importance of pharmacogenetic studies in Mexican populations. The aims of this study were to analyze the reported frequencies of the most relevant pharmacogenetic biomarkers and metabolic phenotypes in healthy volunteers from Mexican populations and to assess its interethnic variability across MI and MM populations. After a literature search in PubMed, and according to previously defined inclusion criteria, 63 pharmacogenetic studies performed in Mexican healthy volunteers up to date were selected. These reports comprised 56,292 healthy volunteers (71.58% MM). Allele frequencies in 31 pharmacogenetic biomarkers, from 121 searched, are described. Nine of these biomarkers presented variation within MM and MI groups. The frequencies of CYP2D6*3, *4, *5, *10, *17, *35 and *41 alleles in the MM group were different from those reported in the MI group. CYP2C9*2 and *3 alleles were more frequent in MM than in MI populations (χ2 test, p<0.05). CYP2C19*3 allele was not found in the MM or MI populations reported. For UGT1A1*28, only one study was found. HLA-A*31:01 and HLA-B*15:02 were present in some MM and MI populations. Poor metabolizers for CYP2D6 and CYP2C9 were more frequent in MM than in MI groups (χ2 test, p<0.05). Only 26% of the relevant pharmacogenetic biomarkers searched have been studied in Mexican healthy volunteers; therefore, further studies are warranted. The frequency variation of biomarkers in MM and MI populations could be important for the clinical implementation of pharmacogenetics in Mexico.

Effect of CYP2C19 Gene Polymorphisms on Proton Pump Inhibitor, Amoxicillin, and Levofloxacin Triple Therapy for Eradication of Helicobacter Pylori

BACKGROUND The effects of PPI are variable owing to the CYP2C19 polymorphisms. However, whether the polymorphisms could affect the Hp eradication efficacy of triple therapy is still not clear. The present study aimed to assess the effects of CYP2C19 gene polymorphisms on proton pump inhibitor (PPI), amoxicillin, and levofloxacin triple therapy for Helicobacter pylori (Hp) eradication. MATERIAL AND METHODS We randomly assigned 160 Hp-positive patients with chronic gastritis to 2 groups to receive either 20 mg bid omeprazole (OAL group, n=80) or 10 mg bid rabeprazole (RAL group, n=80), combined with 1000 mg bid amoxicillin and 500 mg qd levofloxacin. The 2 groups were treated for 10 days. The CYP2C19 genotypes included wild-type, M1 mutant gene (*2, the mutation of exon 5), and M2 mutant gene (*3, the mutation of exon 4) identified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFIP). According to CYP2C19 genotype combinations, the patients were divided into extensive metabolizer (EM), intermediate metabolizer (IM), and poor metabolizer (PM) subgroups. The eradication efficacy of Hp was evaluated by 14C-UBT at 28 days after treatment. RESULTS The trial was completed by 155 patients. Hp eradication rates in OAL and RAL groups were 78.2% and 88.3%, respectively, on per-protocol (PP) analysis, indicating no significant difference (P>0.05). Regarding CYP2C19 genotypes, eradication rates of 60.7%, 84.2%, and 100% were obtained for EM, IM, and PM subgroups, respectively, of the OAL group. EM group eradication rates were significantly lower than IM and PM group values (P<0.05). In the RAL group, no such difference was observed (P>0.05). Hp eradication rates were significantly lower in the EM subgroup of the OAL group compared with that of the RAL group. CONCLUSIONS Hp eradication rates were higher in the RAL group than in OAL-treated patients. Interestingly, omeprazole-based therapy was significantly affected by the CYP2C19 genotype, unlike the rabeprazole-based therapy.

Effect of antituberculosis treatment on CYP2C19 enzyme activity in genetically polymorphic South Indian Tamilian population

Patients on antituberculosis therapy (ATT) are more prone to drug interactions in the presence of coexisting illnesses which require drug therapy. Rifampicin is a pleiotropic inducer of CYP enzymes, and isoniazid is an enzyme inhibitor. Genetic variations are common in the gene coding for CYP2C19 enzyme. These variations would be important in predicting the individual variations in CYP2C19 activity. The objectives of the study were to find the net effect of 1-month ATT on CYP2C19 enzyme activity and its association with CYP2C19 genetic polymorphisms. Newly diagnosed tuberculosis patients (n = 125) were included in the study. Before commencing ATT, they were given a single dose of omeprazole 20 mg as a probe drug for CYP2C19. Blood sample was collected after 3 h to carry out phenotyping for CYP2C19 enzyme by measuring omeprazole hydroxylation index (OHI) using LC-MS/MS. The phenotyping procedure was repeated after 1 month of ATT. CYP2C19 genotyping was carried out by PCR-RFLP method. Significant reduction in OHI was observed after 1 month of ATT in all the metabolizer groups. The percentage reduction in OHI was maximum with poor metabolizers, 84.1 (IQR - 74.6, 86.6), and minimum with ultra-rapid metabolizers, 39.6 (IQR - 12.7, 54.7). CYP2C19 enzyme induction is predominant in patients after 1 month of antituberculosis treatment (ATT). Genetic variations in the enzyme could not clearly explain the interindividual differences in induction. There is a potential risk of drug failure/adverse effect in poor metabolizers regardless of their genotype after ATT.

Genetic variability of CYP2C19 in a Mexican population: contribution to the knowledge of the inheritance pattern of CYP2C19*17 to develop the ultrarapid metabolizer phenotype

CYP2C19 is a polymorphic enzyme that metabolizes a wide variety of therapeutic drugs that has been associated with altered enzymatic activity and adverse drug reactions. Differences in allele frequencies of the CYP2C19 gene have been detected in populations worldwide. Thus, we analysed the alleles CYP2C19*2, CYP2C19*3, CYP2C19*4 and CYP2C19*5 related to the poor metabolizer (PM) phenotype in a Mexican population sample (n = 238), as well as CYP2C19*17, unique allele related to ultrarapid metabolizer phenotype (UMs). Genotypes were determined using SNaPshot and TaqManqPCR assays. In addition to the wild-type CYP2C19*1 allele (77.1%), we only found CYP2C19*17 (14.3%) and CYP2C19*2 (8.6%). Comparison with previous population reports demonstrated that these two SNPs are homogeneously distributed in Latin America (P > 0.05). Based on comparison with a previous pharmacokinetic study that determined the frequency of CYP2C19 phenotypes in the same population (western Mexican), we obtained the following findings: (i) based on the difference between the frequency of genotypes CYP2C19*2/*2 (presumably PM) versus the observed prevalence of PM phenotypes (0.4 versus 6.3%; Χ(2) = 9.58, P = 0.00196), we inferred the plausible presence of novel CYP2C19 alleles related to the PM phenotype; (ii) the prevalence of UMs was in disagreement with the dominant inheritance pattern suggested for CYP2C19*17 (23.1 versus 4%; P < 0.00001); (iii) the apparent recessive inheritance pattern of CYP2C19*17, based on the agreement between homozygous CYP2C19*17/*17 (presumably UMs) and the observed prevalence of UMs (2.1 versus 4%; (Χ(2) = 1.048; P = 0.306).

Pharmacogenetics in Central American healthy volunteers: interethnic variability

Ethnicity is one of the major factors involved in interindividual variability to drug response. This study aims to describe the frequency of the most relevant pharmacogenetic biomarkers and metabolic phenotypes in Central American healthy volunteers and to determine its interethnic variability. Twenty-six original research articles on allelic, genotypes or metabolic phenotype frequencies were analyzed, in which a total number of 7611 Central American healthy volunteers were included (6118 were analyzed for genotype and 1799 for metabolic phenotype). No reports were available for population from Belize and Honduras. The CYP2D6*4 and *5 frequencies in Amerindian populations from Costa Rica have shown to be among the highest frequencies so far reported in the world. Furthermore, NAT2*5 and *6 presented higher frequencies in admixed populations than in Amerindians, but, inversely, the NAT2*7 was more frequent in Amerindians compared to an admixed population. Likewise, different patterns of distribution have been shown in HLA-A*02, *03 and HLA-B*07 among Native populations from Latin America. Reports on Central American populations were also found for the CYP2C19, LDLR, CYP2E1, MDR1, G6PD, TP53, CYP1A2, CYP3A4 and CYP3A5 biomarkers, but no data were available for the other 91 pharmacogenetic biomarkers revised in Central American populations. Differences in the frequency of some pharmacogenetic biomarkers and metabolic phenotypes were found, showing interethnic variability within Central American and with other Latin American populations.

Interethnic variation of CYP2C19 alleles, 'predicted' phenotypes and 'measured' metabolic phenotypes across world populations

The present study evaluates the worldwide frequency distribution of CYP2C19 alleles and CYP2C19 metabolic phenotypes ('predicted' from genotypes and 'measured' with a probe drug) among healthy volunteers from different ethnic groups and geographic regions, as well as the relationship between the 'predicted' and 'measured' CYP2C19 metabolic phenotypes. A total of 52 181 healthy volunteers were studied within 138 selected original research papers. CYP2C19*17 was 42- and 24-fold more frequent in Mediterranean-South Europeans and Middle Easterns than in East Asians (P<0.001, in both cases). Contrarily, CYP2C19*2 and CYP2C19*3 alleles were more frequent in East Asians (30.26% and 6.89%, respectively), and even a twofold higher frequency of these alleles was found in Native populations from Oceania (61.30% and 14.42%, respectively; P<0.001, in all cases), which may be a consequence of genetic drift process in the Pacific Islands. Regarding CYP2C19 metabolic phenotype, poor metabolizers (PMs) were more frequent among Asians than in Europeans, contrarily to the phenomenon reported for CYP2D6. A correlation has been found between the frequencies of CYP2C19 poor metabolism 'predicted' from CYP2C19 genotypes (gPMs) and the poor metabolic phenotype 'measured' with a probe drug (mPMs) when subjects are either classified by ethnicity (r=0.94, P<0.001) or geographic region (r=0.99, P=0.002). Nevertheless, further research is needed in African and Asian populations, which are under-represented, and additional CYP2C19 variants and the 'measured' phenotype should be studied.

Impact of visceral leishmaniasis and curative chemotherapy on cytochrome P450 activity in Brazilian patients

AIMS

The aim of the present study was to investigate the impact of human visceral leishmaniasis (VL) and curative chemotherapy on the activity of cytochrome P450 (CYP) 3A, CYP2C9 and CYP2C19 in patients from an endemic region in Brazil.

METHODS

Adult patients with parasitologically confirmed VL were given a CYP phenotyping cocktail, comprising midazolam, omeprazole and losartan, immediately before (Study phase 1), 2-3 days (phase 2) and 3-6 months (phase 3) after curative VL chemotherapy. CYP activity was assessed by the apparent clearance of midazolam (CYP3A), omeprazole/5-hydroxyomeprazol ratio in plasma (CYP2C19) and losartan/E3174 ratio in urine (CYP2C9).

RESULTS

Mean values (95% confidence interval) in phases 1, 2 and 3 were, respectively: log apparent midazolam clearance, 1.21 (1.10-1.31), 1.45 (1.32-1.57) and 1.35 (1.26-1.44) ml min(-1)  kg(-1) ; omeprazole/5-hydroxyomeprazole ratio, 0.78 (0.61-0.94), 0.45 (0.27-0.63) and 0.37 (0.20-0.55); losartan/E3174 ratio, 0.66 (0.39-0.92), 0.35 (0.20-0.50) and 0.35 (0.16-0.53). Analysis of variance revealed significant differences in CYP3A (P = 0.018) and CYP2C19 (P = 0.008), but not CYP2C9 (P = 0.11) phenotypic activity, across the three study phases.

CONCLUSION

The phenotypic activities of CYP3A4 and CYP2C19 were significantly reduced during acute VL compared with post-chemotherapy. We propose that increased plasma concentrations of proinflammatory cytokines during active disease account for the suppression of CYP activity. The failure to detect significant changes in CYP2C9 activity in the overall cohort may reflect differential effects of the inflammatory process on the expression of CYP isoforms, although the possibility of insufficient statistical power cannot be dismissed.

Hydroxylation index of omeprazole in relation to CYP2C19 polymorphism and sex in a healthy Iranian population

BACKGROUND

Polymorphism of CYP2C19 gene is one of the important factors in pharmacokinetics of CYP2C19 substrates. Omeprazole is a proton pump inhibitor which is mainly metabolized by cytochrome P450 2C19 (CYP2C19). The aim of present study was to assess omeprazole hydroxylation index as a measure of CYP2C19 activity considering new variant allele (CYP2C19*17) in Iranian population and also to see if this activity is sex dependent.

METHODS

One hundred and eighty healthy unrelated Iranian individuals attended in this study. Blood samples for genotyping and phenotyping were collected 3 hours after administration of 20 mg omeprazole orally. Genotyping of 2C19 variant alleles *2, *3 and *17 was performed by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and semi-nested PCR methods. Plasma concentrations of omeprazole and hydroxyomeprazole were determined by high performance liquid chromatography (HPLC) technique and hydxroxylation index (HI) (omeprazole/ hydroxyomeprazole) was calculated.

RESULTS

The CYP2C19*17 was the most common variant allele in the studied population (21.6%). Genotype frequencies of CYP2C19*17*17, *1*17, and *2*17 were 5.5%, 28.8% and 3.3% respectively. The lowest and the highest median omeprazole HI was observed in *17*17 and *2*2 genotypes respectively (0.36 vs. 13.09). The median HI of omeprazole in subjects homozygous for CYP2C19*1 was 2.16-fold higher than individuals homozygous for CYP2C19*17 (P < 0.001) and the median HI of CYP2C19*1*17 genotype was 1.98-fold higher than CYP2C19 *17*17 subjects (P < 0.001). However, subjects with CYP2C19*2*17 (median HI: 1.74) and CYP2C19*1*2 (median HI: 1.98) genotypes and also CYP2C19*1*17 (median HI: 0.71) and CYP2C19*1*1 (mean HI: 0.78) did not show any significantly different enzyme activity. In addition, no statistically significant difference was found between women and men in distribution of CYP2C19 genotypes. Furthermore, the hydroxylation index of Omeprazole was not different between women and men in the studied population.

CONCLUSION

Our data point out the importance of CYP2C19*2 and CYP2C19*17 variant alleles in metabolism of omeprazole and therefore CYP2C19 activity. Regarding the high frequency of CYP2C19*17 in Iranian population, the importance of this new variant allele in metabolism of CYP2C19 substrates shall be considered.

Present status and perspective of pharmacogenetics in Mexico

Drug costs account for up to 24% of the country's health expenditure and there are 13,000 registered drugs being prescribed. Diabetes is the main cause of death in the country, with over 85% of diabetic patients currently under drug treatment. The importance of knowing interindividual variability in drug metabolism on Mexican populations is thus evident. The purpose of this article is to provide an overlook of the current situation of pharmacogenetic research in Mexico, focusing on drug-metabolizing enzymes, and the possibility of developing a phenotyping cocktail for Mexican populations. So far, 21 pharmacogenetic studies on Mexican population samples (Mestizos and Amerindian) have been published. These have reported interindividual variability through phenotyping and/or genotyping cytochromes: CYP2D6, 2C19, 2C9, 2E1, and phase II enzymes UGT and NAT2. Some cytochromes with important clinical implications have not yet been phenotyped in Mexican populations. The development of a cocktail adapted to them could be a significant contribution to a larger knowledge on drug response variability at a lower price and shorter time. There are validated phenotyping cocktails that present several practical advantages, being valuable, safe, and inexpensive tools in drug metabolism characterization, which require only a single experiment to provide information on several cytochrome activities.

Herbal medicines in Brazil: pharmacokinetic profile and potential herb-drug interactions

A plethora of active compounds found in herbal medicines can serve as substrate for enzymes involved in the metabolism of xenobiotics. When a medicinal plant is co-administered with a conventional drug and little or no information is known about the pharmacokinetics of the plant metabolites, there is an increased risk of potential herb-drug interactions. Moreover, genetic polymorphisms in a population may act to predispose individuals to adverse reactions. The use of herbal medicines is rapidly increasing in many countries, particularly Brazil where the vast biodiversity is a potential source of new and more affordable treatments for numerous conditions. Accordingly, the Brazilian Unified Public Health System (SUS) produced a list of 71 plant species of interest, which could be made available to the population in the near future. Physicians at SUS prescribe a number of essential drugs and should herbal medicines be added to this system the chance of herb-drug interactions further increases. A review of the effects of these medicinal plants on Phase 1 and Phase 2 metabolic mechanisms and the transporter P-glycoprotein was conducted. The results have shown that approximately half of these medicinal plants lack any pharmacokinetic data. Moreover, most of the studies carried out are in vitro. Only a few reports on herb-drug interactions with essential drugs prescribed by SUS were found, suggesting that very little attention is being given to the safety of herbal medicines. Here we have taken this information to discuss the potential interactions between herbal medicines and essential drugs prescribed to Brazilian patients whilst taking into account the most common polymorphisms present in the Brazilian population. A number of theoretical interactions are pinpointed but more pharmacokinetic studies and pharmacovigilance data are needed to ascertain their clinical significance.

Efavirenz-mediated induction of omeprazole metabolism is CYP2C19 genotype dependent

Efavirenz increases CYP2C19- and CYP3A-mediated omeprazole metabolism. We hypothesized that CYP2C19 and CYP2B6 genetic polymorphisms influence the extent of induction of omeprazole metabolism by efavirenz. Healthy subjects (n=57) were administered a single 20mg oral dose of omeprazole with a single dose (600mg) or after multiple doses (600mg/day for 17 days) of efavirenz. DNA was genotyped for CYP2C19*2, *3 and *17 alleles and CYP2B6*6, *4 and *9 alleles using Taqman assays. Omeprazole, its enantiomers and metabolites were measured by LC/MS/MS. Our results showed that efavirenz increased omeprazole clearances in all CYP2C19 genotypes in non-stereoselective manner, but the magnitude of induction was genotype-dependent. Metabolic ratios of 5-hydroxylation of omeprazole were reduced in extensive and intermediate metabolizers of CYP2C19 (p<0.05). No significant associations were observed between CYP2B6 genotypes and induction by efavirenz on omeprazole metabolism. Our data indicate how interplays between drug interactions and CYP2C19 genetic variations may influence systemic exposure of CYP2C19 substrates.

The Clinical Pharmacokinetics of Phosphodiesterase-5 Inhibitors for Erectile Dysfunction

Differences in the clinical pharmacology of the 3 currently available oral phosphodiesterase-5 (PDE5) inhibitors, sildenafil, vardenafil, and tadalafil, are largely determined by their clinical pharmacokinetics as well as their PDE inhibitory activity profile. This review comparatively discusses the major characteristics of the pharmacokinetic profile of all 3 PDE5 inhibitors, including bioavailability and rate of absorption, Biopharmaceutical Classification System categorization, elimination mechanisms, and metabolic profile including active metabolites, as well as the drug-drug interaction potential and modification of pharmacokinetic properties under selected physiologic and pathophysiologic conditions. The review is aimed at providing comparative clinical pharmacology data to allow for scientifically rational, evidence-based prescribing and dosing decisions regarding the clinical use of these medications for the treatment of erectile dysfunction.

Distribution of CYP2D6 and CYP2C19 polymorphisms associated with poor metabolizer phenotype in five Amerindian groups and western Mestizos from Mexico

BACKGROUND

The distribution of polymorphisms in the CYP2D6 and CYP2C19 genes allows inferring the potential risk for specific adverse drug reactions and lack of therapeutic effects in humans. This variability shows differences among human populations. The aim of this study was to analyze single-nucleotide polymorphisms related to a poor metabolizer (PM) phenotype in nonpreviously studied Amerindian groups and Mestizos (general admixed population) from Mexico.

METHODS

We detected by SNaPshot(®) different polymorphisms located in CYP2D6 (*3, *4, *6, *7, and *8) and CYP2C19 (*2, *3, *4 and *5) in western Mestizos (n=145) and five Amerindian groups from Mexico: Tarahumaras from the North (n=88); Purépechas from the Center (n=101); and Tojolabales (n=68), Tzotziles (n=88), and Tzeltales (n=20) from the Southeast. Genotypes were observed by capillary electrophoresis. The genetic relationships among these populations were estimated based on these genes.

RESULTS AND DISCUSSION

The wild-type allele (*1) of both genes was predominant in the Mexican populations studied. The most widely observed alleles were CYP2C19*2 (range, 0%-31%) and CYP2D6*4 (range, 1.2%-7.3%), whereas CYP2D6*3 was exclusively detected in Mestizos. Conversely, CYP2C19*4 and *5, as well as CYP2D6*3, *6, *7, and *8, were not observed in the majority of the Mexican populations. The Tarahumaras presented a high frequency of the allele CYP2C19*2 (31%) and of homozygotes *2/*2 (10.7%), which represent a high frequency of potentially PM phenotypes in this Amerindian group. The genetic distances showed high differentiation of Tarahumaras (principally for CYP2C19 gene). In general, a relative proximity was observed between most of the Amerindian, Mexican-Mestizo, and Latin-American populations.

CONCLUSION

In general, the wild-type allele (*1) predominates in Mexican populations, outlining a relatively homogeneous distribution for CYP2C19 and CYP2D6. The exception is the Tarahumara group that displays a potentially increased risk for adverse reactions to CYP2C19-metabolized drugs.

CYP3A5 polymorphism in Mexican renal transplant recipients and its association with tacrolimus dosing

BACKGROUND AND AIMS

Variability in CYP3A5 expression associated with differences in tacrolimus bioavailability has been documented. The wild-type allele CYP3A5*1 expresses the functional protein, whereas the CYP3A5*3 allele is a splice variant with a premature stop codon and encodes a truncated nonfunctional protein. The aim of the study was to determine the frequency of CYP3A5*1 and CYP3A5*3 in 291 (124 adults, 167 pediatric) Mexican renal transplant recipients, evaluate the tacrolimus dose requirements by genotype and compare genotype frequency data with that of other populations.

METHODS

We carried out a multicenter study. Patients were recruited from three institutions located in Mexico City. Genotyping of the CYP3A5*1 and CYP3A5*3 alleles was performed by direct DNA sequencing.

RESULTS

Eighteen patients (6.2%) were CYP3A5*1*1 homozygous carriers or functional protein expresser homozygous, 121 patients (41.6 %) were CYP3A5*1*3 were heterozygous carriers or heterozygous expressers, and 152 patients (52.2%) were CYP3A5*3*3 homozygous carriers or homozygous nonexpressers. There was a statistically significant difference in frequency of the functional and nonfunctional expresser phenotypes from those reported for Black and Caucasian, but not for South Asian populations. The CYP3A5 phenotype had a significant impact in tacrolimus bioavailability, as wild-type carriers required higher dosing compared to mutated carriers to achieve similar drug trough levels. Patients with CYP3A5*1*1 genotype had a median dose requirement of 0.16 mg/kg/day, CYP3A5*1*3 patients had a median tacrolimus dose of 0.13 mg/kg/day and CYP3A5*3*3 had a median dose of 0.07 mg/kg/day (Kruskal-Wallis, p <0.0001).

CONCLUSIONS

Of the Mexican transplant recipients, 52.2% were CYP3A5*3*3 and required significantly lower tacrolimus dose than those with CYP3A5*1 allele.

Induction of CYP2C19 and CYP3A activity following repeated administration of efavirenz in healthy volunteers

Drug-drug interactions involving efavirenz are of major concern in clinical practice. We evaluated the effects of multiple doses of efavirenz on omeprazole 5-hydroxylation (CYP2C19) and sulfoxidation (CYP3A). Healthy volunteers (n = 57) were administered a single 20 mg oral dose of racemic omeprazole either with a single 600 mg oral dose of efavirenz or after 17 days of administration of 600 mg/day of efavirenz. The concentrations of racemic omeprazole, 5-hydroxyomeoprazole (and their enantiomers), and omeprazole sulfone in plasma were measured using a chiral liquid chromatography-tandem mass spectrometry method. Relative to single-dose treatment, multiple doses of efavirenz significantly decreased (P < 0.0001) the area under the plasma concentration-time curve from 0 to infinity (AUC(0-∞)) of racemic-, R- and S-omeprazole (2.01- to 2.15-fold) and the corresponding AUC(0-∞) metabolic ratio (MR) for 5-hydroxyomeprazole (1.36- to 1.44-fold) as well as the MR for omeprazole sulfone (∼2.0) (P < 0.0001). The significant reduction in the AUC of 5-hydroxyomeprazole after repeated efavirenz dosing suggests induction of sequential metabolism and mixed inductive/inhibitory effects of efavirenz on CYP2C19. In conclusion, efavirenz enhances omeprazole metabolism in a nonstereoselective manner through induction of CYP3A and CYP2C19 activity.

Buspirone, fexofenadine, and omeprazole: quantification of probe drugs and their metabolites in human plasma

Probe drugs are critical tools for the measurement of drug metabolism and transport activities in human subjects. Often several probe drugs are administered simultaneously in a "cocktail". This cocktail approach requires efficient analytical methods for the simultaneous quantitation of multiple analytes. We have developed and validated a liquid chromatography-tandem mass spectrometry method for the simultaneous determination of three probe drugs and their metabolites in human plasma. The analytes include omeprazole and its metabolites omeprazole sulfone and 5'-hydroxyomeprazole; buspirone and its metabolite 1-[2-pyrimidyl]-piperazine (1PP); and fexofenadine. These analytes and the internal standard lansoprazole were extracted from plasma using protein precipitation with acetonitrile. Gradient reverse-phase chromatography was performed with 7.5mM ammonium bicarbonate and acetonitrile, and the analytes were quantified in positive ion electrospray mode with multiple reaction monitoring. The method was validated to quantify the concentration ranges of 1.0-1000ng/ml for omeprazole, omeprazole sulfone, 5'-hydroxyomeprazole, and fexofenadine; 0.1-100ng/ml for buspirone, and 1.0-100ng/ml for 1PP. These linear ranges span the plasma concentrations for all of the analytes from probe drug studies. The intra-day precision was between 2.1 and 16.1%, and the accuracy ranged from 86 to 115% for all analytes. Inter-day precision and accuracy ranged from 0.3 to 14% and from 90 to 110%, respectively. The lower limits of quantification were 0.1ng/ml for buspirone and 1ng/ml for all other analytes. This method provides a fast, sensitive, and selective analytical tool for quantification of the six analytes in plasma necessary to support the use of this probe drug cocktail in clinical studies.

Interaction of sorafenib and cytochrome P450 isoenzymes in patients with advanced melanoma: a phase I/II pharmacokinetic interaction study

BACKGROUND

In vitro data indicate that the sorafenib is a moderate inhibitor of cytochrome P450 (CYP) enzymes, including CYP3A4, CYP2C19, and CYP2D6. This phase I/II study in patients with advanced melanoma evaluated the potential effect of sorafenib on the pharmacokinetics of midazolam, omeprazole, and dextromethorphan, specific substrates of CYP3A4, CYP2C19, and CYP2D6, respectively.

METHODS

Twenty-one patients received sorafenib 400 mg twice daily for 28 consecutive days. On days 1 and 28, a cocktail containing midazolam 2 mg, omeprazole 20 mg, and dextromethorphan 30 mg was administered. Pharmacokinetic analyses were performed on day 1 without sorafenib and day 28 after steady-state sorafenib exposure; sorafenib pharmacokinetics were evaluated on day 28. We defined an interaction to be excluded if the 90% confidence interval of the ratio of all day 28:day 1 analyses fell within a range from 0.80 to 1.25.

RESULTS

In all, 18 patients were evaluable. On day 28, area under the plasma concentration-time curve from time 0 to 12 h (AUC(0-12)) and maximum plasma concentration (C(max)) for sorafenib were 38.1 mg h/l and 4.9 mg/l, respectively. Day 28:day 1 ratios for AUC from time 0 extrapolated to infinity (AUC(0-inf)) and C(max) for midazolam were 0.85 and 0.98, respectively. Day 28:day 1 ratio for 5-OH-omeprazole:omeprazole plasma concentration at 3 h postdose was 1.26, slightly outside of the 0.80-1.25 range. Thus, an interaction could not be excluded, but is considered unlikely to be clinically significant. Day 28:day 1 ratio for dextromethorphan:dextrorphan concentration in urine was 0.94. Sorafenib had an acceptable safety profile. The most frequently observed grade 3-4 toxicities in cycle 1 included elevated lipase (19%) and hypertension (10%).

CONCLUSIONS

In this patient population, our results demonstrate that exposures of probes of CYP3A4, CYP2D6, or CYP2C19 activity are potentially altered by administration of sorafenib at 400 mg twice daily. However, these differences are sufficiently small that a clinically significant inhibition or induction of these important drug metabolizing P450 isoenzymes is unlikely. Clinical and, where possible, drug level monitoring may still be appropriate for drugs of narrow therapeutic range co-administered with sorafenib.

Relation between CYP2C19 phenotype and genotype in a group of Brazilian volunteers

The CYP2C19 gene presents polymorphism affecting the pharmacokinetics of several drugs of clinical importance. The purpose of this study was to investigate the correlation between CYP2C19 genotype and metabolic phenotype in a group of 38 Brazilian volunteers, evaluating the phenotype prediction capacity of the genotyping procedure. For CYP2C19 phenotyping, omeprazole was used as the probe drug, using the hydroxylation metabolic ratio as the phenotypic indicator. Venous blood samples were drawn before and three hours after an oral administration of 20 mg omeprazole. The plasma concentrations of omeprazole and hydroxy-omeprazole were determined by high performance liquid chromatography. The genotyping assay was carried out using a Real-Time-PCR-based assay, identifying the alleles *1 (completely functional), *2, *3 and *4 (null). The phenotyping procedure estimated the presence of 4 poor, 34 extensive and 1 ultra-extensive metabolizer. The genotyping identified 4 poor, 23 extensive and 11 intensive metabolizers. The groups of volunteers classified according to the number of active alleles of CYP2C19 had significant differences in the metabolic ratios of omeprazole hydroxylation. However, volunteers exhibiting the same number of active alleles presented different phenotypes. Therefore, the phenotyping of CYP2C19 is a more promising alternative to dose individualization of CYP2C19 substrate drugs.

Investigation of the in vivo activity of CYP3A in Brazilian volunteers: comparison of midazolam and omeprazole as drug markers

OBJECTIVE

This study compares midazolam with omeprazole as marker drugs for the evaluation of CYP3A activity in nine healthy self-reported white Brazilian volunteers.

METHODS

Omeprazole was also used to evaluate the CYP2C19 phenotype. The volunteers received p.o. 20 mg omeprazole, and blood samples were collected 3.5 h after drug administration. After a washout period of 10 days, the volunteers received p.o. 15 mg midazolam maleate, and serial blood samples were collected up to 6 h after administration of the drug. CYP2C19 was genotyped for the allelic variants CYP2C19*1, CYP2C19*2, CYP2C19*3, and CYP2C19*17. Analysis of omeprazole, hydroxyomeprazole, omeprazole sulfone, and midazolam in plasma was carried out by LC-MS/MS.

RESULTS

The volunteers genotyped as CYP2C19*1*17, CYP2C19*17*17, CYP2C19*1*1 (n = 8), or CYP2C19*17*2 (n = 1) presented a median hydroxylation index (omeprazole/hydroxyomeprazole) of 1.35, indicating that all of them were extensive metabolizers of CYP2C19. The volunteers (n = 9) presented a 0.12 log of the omeprazole/sulfone ratio and a median oral clearance of midazolam of 17.89 ml min(-1) kg(-1), suggesting normal CYP3A activity.

CONCLUSIONS

Orthogonal regression analysis between midazolam clearance and log of the plasma concentrations of the omeprazole/omeprazole sulfone ratio (R = -0.7544, P < 0.05) suggests that both midazolam and omeprazole can be used as markers of CYP3A activity in the population investigated.

The effect of CYP2C19 polymorphism on the pharmacokinetics and pharmacodynamics of clopidogrel: a possible mechanism for clopidogrel resistance

We evaluated the effect of the CYP2C19 genotype on the pharmacokinetics and pharmacodynamcis of clopidogrel. Twenty-four subjects were divided into three groups on the basis of their CYP2C19 genotype: homozygous extensive metabolizers (homoEMs, n = 8), heterozygous EMs (heteroEMs, n = 8), and poor metabolizers (PMs, n = 8). After a single 300-mg loading dose of clopidogrel on day 1, followed by a 75-mg daily maintenance dose from days 2 to 7, we measured the plasma levels of clopidogrel and assessed the antiplatelet effect as pharmacodynamics. The mean clopidogrel area under the curve (AUC) for PMs was 1.8- and 2.9-fold higher than that for heteroEMs and homoEMs, respectively (P = 0.013). The mean peak plasma concentration in PMs was 1.8- and 4.7-fold higher than that of heteroEMs and homoEMs, respectively (P = 0.008). PMs exhibited a significantly lower antiplatelet effect than heteroEMs or homoEMs (P < 0.001). From these findings it is clear that the CYP2C19 genotype affects the plasma levels of clopidogrel and modulates the antiplatelet effect of clopidogrel.

Phenotype-genotype analysis of CYP2C19 in Colombian mestizo individuals

Background

Omeprazole is metabolized by the hepatic cytochrome P450 (CYP) 2C19 enzyme to 5-hydroxyomeprazole. CYP2C19 exhibits genetic polymorphisms responsible for the presence of poor metabolizers (PMs), intermediate metabolizers (IMs) and extensive metabolizers (EMs). The defective mutations of the enzyme and their frequencies change between different ethnic groups; however, the polymorphism of the CYP2C19 gene has not been studied in Colombian mestizos. The aim of this study was to evaluate the genotype and phenotype status of CYP2C19 in Colombian mestizos, in order to contribute to the use of appropriate strategies of drug therapy for this population.

Methods

189 subjects were genotyped using the multiplex SNaPshot technique and a subgroup of 44 individuals received 20 mg of omeprazole followed by blood collection at 3 hours to determine the omeprazole hydroxylation index by HPLC.

Results

83.6%, 15.3% and 1.1% of the subjects were genotyped as EMs, IMs and PMs, respectively. The frequencies of the CYP2C29*1 and CYP2C19*2 alleles were 91.3% and 8.7% respectively whereas the *3, *4, *5, *6 and *8 alleles were not found. No discrepancies were found between the genotype and phenotype of CYP2C19.

Conclusion

The frequency of poor metabolizers (1.1%) in the Colombian mestizos included in this study is similar to that in Bolivian mestizos (1%) but lower than in Mexican-Americans (3.2%), West Mexicans (6%), Caucasians (5%) and African Americans (5.4%). The results of this study will be useful for drug dosage recommendations in Colombian mestizos.

Use of omeprazole sulfone in a single plasma sample as a probe for CYP3A4

OBJECTIVE

The hydroxylation of omeprazole, measured as the ratio of omeprazole/5-hydroxyomeprazole in a plasma sample taken 3 h after an oral dose, is an established method to determine CYP2C19 activity, and the ratio of omeprazole AUC/omeprazole sulfone AUC has been used for assessing CYP3A4 activity. The aim of this study was to determine whether the latter ratio from a single 3-h sample can also be used for CYP3A4 phenotyping.

METHODS

Plasma levels of omeprazole and omeprazole sulfone were analyzed by reversed-phase high-performance liquid chromatography in a blood sample drawn 3 h after intake of a single oral 20-mg dose of omeprazole by 22 healthy subjects and five patients with newly diagnosed epilepsy. The procedure was repeated on the 4th day of 200 mg of ketoconazole intake (10 subjects), after 3 weeks of 150-200 mg twice-daily carbamazepine (five patients), and on the 6th day of 4 mg twice-daily tolterodine (12 subjects). Five subjects also took 100 mg and 50 mg of ketoconazole for 3 days before concomitant intake with omeprazole.

RESULTS

The mean log10(omeprazole/omeprazole sulfone) ratio was 0.18 3 h after intake of omeprazole alone. After concomitant intake of ketoconazole, the corresponding value was 1.38 (p<0.001); after intake of carbamazepine it was -0.42 (p<0.05); and after tolterodine it was 0.29 (not significant). In the five subjects taking increasing doses of ketoconazole, the ratio was 0.11, 0.79, 1.2, and 1.5 after 0, 50, 100, and 200 mg of ketoconazole, respectively. The correlation between the metabolic ratios from the AUC((0-6h)) and from the single 3-h samples was very good, with a correlation coefficient of 0.92 (p<0.001).

CONCLUSIONS

A single blood sample taken 3 h after intake of 20 mg of omeprazole can be reliably used to phenotype for both CYP2C19 and CYP3A4 activity.

Papel del polimorfismo genético CYP2C19 en los efectos adversos a fármacos y en el riesgo para diversas enfermedades

There are a great number of polymorphic genes in the human genome. Many of them codify enzymes that metabolizes drugs and xenobiotic agents, including carcinogens. Among the better known of them, there are a number of isozymes of the microsomal oxidative system (CYP3A4, CYP2C9, CYP2C19 y CYP2D6). This article reviews the following issues: a) frequency of presentation of the "poor metabolizer" genotype and/or phenotype for substrates of CYP2C19; b) role of CYP2C19 polymorphism on the metabolism of some drugs (mephenytoine and other antiepileptic drugs, proton pump inhibitors, several antidepressants and anxyolitics, the antimalaria aggent proguanyl, and propranolol, among others, use this metabolic pathway), and c) possible role of CYP2C19 polymorphism in the risk for development of neoplasia and other diseases (systemic lupus erythematosus, psoriasis, hip osteonecrosis, Alzheimer's disease, amyotrophic lateral sclerosis, essential tremor).

Clinical Guidelines for Psychiatrists for the Use of Pharmacogenetic Testing for CYP450 2D6 and CYP450 2C19

Pharmacogenetics has arrived in clinical psychiatric practice with the FDA approval of the AmpliChip CYP450 Test that genotypes for two cytochrome P450 2D6 (CYP2D6) and 2C19 (CYP2C19) genes. Other pharmacogenetic tests, including those focused on pharmacodynamic genes, are far from ready for clinical application. CYP2D6 is important for the metabolism of many antidepressants and antipsychotics, and CY2C19 is important for some antidepressant metabolism. Poor metabolizers (PMs), lacking the enzyme, account for up to 7% of Caucasians for CYP2D6 and up to 25% of East Asians for CYP2C19. Patients having three or more active CYP2D6 alleles (up to 29% in North Africa and the Middle East), are called CYP2D6 ultra-rapid metabolizers (UMs). CYP2D6 phenotypes (particularly PMs) are probably important in patients taking tricyclic antidepressants (TCAs), venlafaxine, typical antipsychotics, and risperidone. The CYP2C19 PM phenotype is probably important in patients taking TCAs and perhaps citalopram, escitalopram, and sertraline. On the basis of the literature and the authors' clinical experience, the authors provide provisional recommendations for identifying and treating CYP2D6 PMs, CYP2C19 PMs, and CYP2D6 UMs. The next few years will determine whether CYP2D6 genotyping is beneficial for patients taking the new drugs aripiprazole, duloxetine, and atomoxetine. Practical recommendations for dealing with laboratories offering CYP2D6 and CYP2C29 genotyping are provided.

Possible Interethnic Differences in Omeprazole Pharmacokinetics

BACKGROUND AND OBJECTIVE

Considerable ethnic differences have been reported in the incidence of the poor metaboliser (PM) genotype of cytochrome P450 (CYP) 2C19. The frequency of this genotype was found to be much higher in Oriental persons (13-23%) than in American or European populations (3-5%). There are, however, no valid data published for Arabic subjects. The present study was conducted to evaluate pharmacokinetic parameters of omeprazole after a single dose in healthy Jordanian Arabic subjects and to compare the results with data published for other populations.

METHODS

Seventy-four healthy male Jordanian Arabic volunteers contributed to the study, which was performed at Al Essra Hospital in Amman, Jordan. After an overnight fast, omeprazole was administered as a single Losec 20mg capsule. A total of 20 blood samples were collected over a 10-hour period after administration. Omeprazole pharmacokinetic parameters were determined from the plasma concentration-time profiles using the WinNonlin software. Kolmogorov-Smirnov's test and probit plots of omeprazole area under the plasma concentration-time curve (AUC) data were used to analyse the frequency distribution of phenotypic data.

RESULTS

The mean pharmacokinetic parameters and their corresponding coefficient of variation (CV%) for peak plasma concentration (Cmax), AUC from time zero to infinity (AUCinfinity), time to reach Cmax (tmax), apparent oral clearance (CL/F) and elimination half-life (t(1/2)) were 314.96 ng/mL (56%), 923.2 ng . h/mL (108.6%), 2.1h (44%), 0.66 L/h/kg (92%) and 1.5 h (56.6%), respectively. Interindividual differences in the current study were high for all pharmacokinetic parameters, yet comparable to CVs reported in nonphenotyped subjects identified within other ethnic groups (40.3-159% for AUC and 39-48.2% for Cmax). The frequency distribution of all parameters, particularly the AUC, was shown to be trimodal. This has proposed the presence of three distinct phenotypes, designated as extensive metabolisers (EMs), slow-extensive metabolisers (SEMs), and PMs, with corresponding frequency of 36.5%, 39.2% and 24.3%, respectively. After stratification, the relative mean AUCs of omeprazole in EMs, SEMs and PMs were 1 : 2.7 : 9.3 (all p < 0.001). Accordingly, the CL/F of omeprazole showed a ratio of 9.8 : 3.6 : 1 for three phenotype groups, respectively. For other pharmacokinetic parameters including Cmax, t1/2, AUC normalised for bodyweight (AUCN), Cmax/dose and AUC/dose, there were also significant differences between the three groups.

CONCLUSIONS

The current pharmacokinetic study revealed that the majority of the Jordanian Arabics seemed to be more properly classified within the EM phenotype. More specifically, the observed metabolic rates of heterozygous and homozygous Jordanian Arabic EMs were more comparable to those of Caucasian EMs than Oriental EMs. Consequently, higher dosage requirements can be expected among most of the Jordanian Arabics. Yet, the incidence of PMs is significant and they seemed to exhibit a similar pharmacokinetic pattern to Chinese PMs in terms of long-term exposure (clearance and AUC) as well as short-term exposure (Cmax) parameters, after adjustment for dose and bodyweight. Therefore, further clinical application of CYP2C19 polymorphism is anticipated in Jordanian Arabic mixed population, particularly if long-term use of omeprazole is intended.

The effect of the CYP2C19 genotype on the hydroxylation index of omeprazole in South Indians

To investigate the relationship between CYP2C19 genotypes and the hydroxylation index (HI) of omeprazole in the South Indian population. Healthy unrelated South Indian subjects (n=300) were separated into three groups based on their CYP2C19 genotypes. They were administered a single oral dose of 20 mg omeprazole, and venous blood was collected 3 h later. Plasma was assayed using reversed-phase high-performance liquid chromatography, and the omeprazole HI was calculated. The means of HIs in individuals with CYP2C19*1/*1 (n=124), *1/*2 (n=129) and *2/*2,*2/*3 (n=47) were 2.4, 5.3 and 22.5, respectively, and were found to be significantly different between any two groups (P<0.0001). A good correlation was established between CYP2C19 genotype and omeprazole HI (r=0.54, 95% CI 0.45-0.62; P<0.0001). Of the 300 subjects, 42 (14.0%; 95% CI 10.1-17.9) were phenotypic poor metabolizers (PMs), but only 33 of them had two mutant alleles and the remaining 9 PMs had at least one wild-type allele. Among the 258 extensive metabolizers, 14 had two mutant alleles. The prevalence of PMs in the South Indian population was 14.0%, which is similar to that in North Indians and Orientals but significantly higher than in Caucasians and Africans. A genotype-phenotype relationship was established between the CYP2C19 genotype and HI of omeprazole, but 7.7% of subjects deviated from expected genotype-phenotype associations. This could be due to an additional mutation, either in the exons/introns or in the 5'-regulatory region of the CYP2C19 gene.