Use of omeprazole as a probe drug for CYP2C19 phenotype in Swedish Caucasians: comparison with S-mephenytoin hydroxylation phenotype and CYP2C19 genotype

CYP2C19 genotypes in the pharmacokinetics/pharmacodynamics of proton pump inhibitor-based therapy of Helicobacter pylori infection

IMPORTANCE OF THE FIELD

Proton pump inhibitors (PPIs) are potent gastric acid inhibitors. Therapies with a PPI and antibiotics are used to cure Helicobacter pylori (H. pylori) infection, which is closely related to many gastrointestinal diseases. Most PPIs are mainly metabolized by cytochrome 2C19 (CYP2C19). The genetic polymorphisms of CYP2C19 may lead to the differences in pharmacokinetics (PK), pharmacodynamics (PD) and clinical efficacy of PPIs.

AREAS COVERED IN THIS REVIEW

The roles of PPIs on the eradication of H. pylori are summarized. The impact f CYP2C19 polymorphism on the PK and PD of PPIs is addressed and related to the present status of therapy for H. pylori infection. The opinions on the strategy of PPIs-based therapies of H. pylori infection are provided.

WHAT THE READER WILL GAIN

Update the factors that may influence the PPIs-based therapies of H. pylori infection.

TAKE HOME MESSAGE

The eradication rates of H. pylori infection are significantly different between patients who are CYP2C19 extensive metabolizers and poor metabolizers, partly because of the differences in the PK and PD of PPIs. Nonetheless, the differences can be improved by adjusting the regimens of PPIs and using antibiotics that have less H. pylori-resistance.

Effect of cytochrome P450 polymorphism on arachidonic acid metabolism and their impact on cardiovascular diseases

Cardiovascular diseases (CVDs) remain the leading cause of death in the developed countries. Taking into account the mounting evidence about the role of cytochrome P450 (CYP) enzymes in cardiovascular physiology, CYP polymorphisms can be considered one of the major determinants of individual susceptibility to CVDs. One of the important physiological roles of CYP enzymes is the metabolism of arachidonic acid. CYP epoxygenases such as CYP1A2, CYP2C, and CYP2J2 metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs) which generally possess vasodilating, anti-inflammatory, anti-apoptotic, anti-thrombotic, natriuretic, and cardioprotective effects. Therefore, genetic polymorphisms causing lower activity of these enzymes are generally associated with an increased risk of several CVDs such as hypertension and coronary artery disease. EETs are further metabolized by soluble epoxide hydrolase (sEH) to the less biologically active dihydroxyeicosatrienoic acids (DHETs). Therefore, sEH polymorphism has also been shown to affect arachidonic acid metabolism and to be associated with CVDs. On the other hand, CYP omega-hydroxylases such as CYP4A11 and CYP4F2 metabolize arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE) which has both vasoconstricting and natriuretic effects. Genetic polymorphisms causing lower activity of these enzymes are generally associated with higher risk of hypertension. Nevertheless, some studies have denied the association between polymorphisms in the arachidonic acid pathway and CVDs. Therefore, more research is needed to confirm this association and to better understand the pathophysiologic mechanisms behind it.

Drug-induced liver injury: insights from genetic studies

Drug-induced liver injury (DILI) is an increasing health problem and a challenge for physicians, regulatory bodies and the pharmaceutical industry, not only because of its potential severity and elusive pathogenesis but also because it is often inaccurately diagnosed, commonly missed entirely and more often not reported. The general view is that idiosyncratic DILI, which is not predictable whether based on the pharmacology of the drug or on the dose administered, is determined by the presence in the recipient of variants in, or expression of, genes coding for key metabolic pathways and/or the immune response, and the interaction of these genetic variants with environmental variables. Furthermore, idiosyncratic DILI is an example of a complex-trait disease with two or more susceptibility loci, as reflected by the frequency of genetic variants in the population often being higher than the occurrence of significant liver injury. Polymorphisms of bioactivation/toxification pathways via the CYP450 enzymes (Phase I), detoxification reactions (Phase II) and excretion/transport (Phase III), together with immunological factors that might determine DILI are reviewed. Challenges such as gene-trait association studies and whole-genome studies, and future approaches to the study of DILI are explored. Better knowledge of the candidate genes involved could provide further insight for the prospective identification of susceptible patients at risk of developing drug-induced hepatotoxicity, development of new diagnostic tools and new treatment strategies with safer drugs.

High frequency of occurrence of CYP2D6 gene duplication/multiduplication indicating ultrarapid metabolism among suicide cases

In Sweden, about 550 individuals die every year of drug intoxication. Many of these drugs are metabolized by CYP enzymes such as CYP2D6 and CYP2C19. A lack of these enzymes, resulting in poor metabolism, can lead to adverse reactions and even to fatality. On the other hand, an ultrarapid metabolism can lead to insufficient drug plasma concentration, resulting in failure of treatment, or it can lead to high concentrations of active/toxic metabolites. The aim of this project was to study the genetic profile of individuals with regard to the presence of CYP2D6 and CYP2C19 genes, in cases of fatal intoxication (242), suicide (intoxications excluded) (262), and natural death (212). PCR, followed by pyrosequencing, was used for all the analyses. We found that, among those who died of suicide (suicide cases), there was a higher number carrying more than two active CYP2D6 genes (corresponding to the phenotype of ultrarapid metabolizer) as compared with those who died of natural causes (natural-death cases) (P = 0.007).

Effects of the CYP3A5 genotype on omeprazole sulfoxidation in CYP2C19 PMs

OBJECTIVE

Omeprazole is metabolized by the two cytochrome P450 isoforms, CYP3A (sulfoxidation) and CYP2C 19 (hydroxydation). The aim of this study was to determine whether the CYP3A5 genotype is an important determinant of inter-individual variability of total CYP3A activity in vivo.

METHODS

Plasma levels of omeprazole and omeprazole sulfone were analyzed by high-performance liquid chromatography in blood samples drawn 4-5 h after 43 CYP2C19 poor metabolizers (PMs) had ingested a single oral 40 mg dose of omeprazole. The CYP3A5*3 allele was identified using a PCR-restriction fragment length polymorphism assay.

RESULTS

Among the 43 CYP2C19 PMs, 24 were CYP3A5*3/*3 carriers and 19 were CYP3A5*1 carriers (CYP3A5*I/*I in one subject and CYP3A5*1/*3 in 18 subjects). No significant difference was found between the mean log10 (metabolic ratio) of the CYP3A5*3/*3 carriers (0.314 +/- 0.369) and CYP3A5*1 carriers (0.330 +/- 0.313).

CONCLUSIONS

The CYP3A5 genotype was not an important factor underlying the inter-individual variation in the metabolic ratio of omeprazole to omeprazole sulfone in our study cohort, although genotype can be considered to be responsible for the inter-individual variation of many CYP3A substrates in vivo.

Maintenance time of sedative effects after an intravenous infusion of diazepam: a guide for endoscopy using diazepam

AIM

To examine whether the sedative effects assessed by psychomotor tests would depend on the cytochrome P450 (CYP) 2C19 genotypes after an infusion regimen of diazepam commonly used for gastrointestinal endoscopy in Japan.

METHODS

Fifteen healthy Japanese volunteers consisting of three different CYP2C19 genotype groups underwent a critical flicker fusion test, an eye movement analysis and a postural sway test as a test for physical sedative effects, and a visual analog scale (VAS) symptom assessment method as a test for mental sedative effects during the 336 h period after the intravenous infusion of diazepam (5 mg).

RESULTS

The physical sedative effects assessed by the critical flicker test continued for 1 h (t values of 5 min, 30 min and 60 min later: 4.35, 5.00 and 3.19, respectively) and those by the moving radial area of a postural sway test continued for 3 h (t values of 5 h, 30 h, 60 min and 3 h later: -4.05, -3.42, -2.17 and -2.58, respectively), which changed significantly compared with the baseline level before infusion (P<0.05). On the other hand, the mental sedative effects by the VAS method improved within 1 h. The CYP2C19 genotype-dependent differences in the postinfusion sedative effects were not observed in any of the four psychomotor function tests.

CONCLUSION

With the psychomotor tests, the objective sedative effects of diazepam continued for 1 h to 3 h irrespective of CYP2C19 genotype status and the subjective sedative symptoms improved within 1 h. Up to 3 h of clinical care appears to be required after the infusion of diazepam, although patients feel subjectively improved.

Global pharmacogenetics: genetic substructure of Eurasian populations and its effect on variants of drug-metabolizing enzymes

AIMS

To study the frequency distribution of cytochrome P450 (CYP) functional genetic variants in five Eurasian populations from the territory of Siberia in Russia.

MATERIALS & METHODS

Unrelated healthy Tuvinians, Buryats, Altaians, Yakuts and Russians (n = 87-88) were genotyped for CYP2C9*2, CYP2C9*3, CYP2C19*2, CYP2C19*3, CYP3A5*3 and CYP3A5*6. Standard pairwise genetic distances, locus-specific and global Fst statistics were calculated.

RESULTS

CYP allele and genotype frequencies demonstrated significant variability. Overall, the degree of between-population variance displayed by CYP SNPs was lower than that recorded from neutral short tandem repeats and Alu-insertion polymorphism, indicating evolutionary conservation of CYP polymorphisms. CYP-based genetic distances were well correlated with the geographic distances across populations (r = 0.822, p = 0.008).

CONCLUSIONS

Although the tested variants were present in the neighboring, yet secluded, populations at the expected range of frequencies, the observed frequencies were significantly variable across Eurasian populations, indicating potential relevance to clinical decision making.

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.

Increased omeprazole metabolism in carriers of the CYP2C19*17 allele; a pharmacokinetic study in healthy volunteers

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

The only existing study of CYP2C19*17-associated alterations in drug pharmacokinetics was retrospective and compared probe drug metabolic ratios. The CYP2C19*17 allele had been associated with a two- and fourfold decrease in omeprazole and S/R-mephenytoin metabolic ratios.

WHAT THIS STUDY ADDS

This study characterized the single-dose pharmacokinetics of omeprazole, along with the 5-hydroxy and sulphone metabolites, in CYP2C19*17/*17 and CYP2C19*1/*1 subjects. The observed differences in omeprazole AUC(infinity) suggest that the CYP2C19*17 allele is an important explanatory factor behind individual cases of therapeutic failure. AIMS To investigate the influence of the CYP2C19*17 allele on the pharmacokinetics of omeprazole, a commonly used CYP2C19 probe drug, in healthy volunteers.

METHODS

In a single-dose pharmacokinetic study, 17 healthy White volunteers genotyped as either CYP2C19*17/*17 or CYP2C19*1/*1 received an oral dose of 40 mg of omeprazole. Plasma was sampled for up to 10 h postdose, followed by quantification of omeprazole, 5-hydroxy omeprazole and omeprazole sulphone by high-performance liquid chromatography.

RESULTS

The mean omeprazole AUC(infinity) of 1973 h nmol l(-1) in CYP2C19*17/*17 subjects was 2.1-fold lower [95% confidence interval (CI) 1.1, 3.3] than in CYP2C19*1/*1 subjects (4151 h nmol l(-1), P = 0.04). A similar trend was observed for the sulphone metabolite with the CYP2C19*17/*17 group having a mean AUC(infinity) of 1083 h nmol l(-1), 3.1-fold lower (95% CI 1.2, 5.5) than the CYP2C19*1/*1 group (3343 h nmol l(-1), P = 0.03). A pronounced correlation (r(2) = 0.95, P < 0.0001) was seen in the intraindividual omeprazole AUC(infinity) and omeprazole sulphone AUC(infinity) values.

CONCLUSIONS

The pharmacokinetics of omeprazole and omeprazole sulphone differ significantly between homozygous CYP2C19*17 and CYP2C19*1 subjects. For clinically important drugs that are metabolized predominantly by CYP2C19, the CYP2C19*17 allele might be associated with subtherapeutic drug exposure.

Treatment strategy to eradicate Helicobacter pylori infection: impact of pharmacogenomics-based acid inhibition regimen and alternative antibiotics

The eradication rates of Helicobacter pylori by the triple therapy consisting of a proton pump inhibitor (PPI) and two antimicrobial agents are mainly influenced by bacterial susceptibility to antimicrobial agents and magnitude of acid inhibition during the treatment with a PPI. Acid inhibition during the treatment is affected by the dosing schemes of acid inhibitory drugs (i.e., PPI), genotypes of drug-metabolizing enzymes (i.e., CYP450 2C19), drug transporters (i.e., multi-drug resistant transporter-1) and inflammatory cytokines (i.e., IL-1 beta). Modification of dosing schedules of a PPI, such as frequent PPI dosing and concomitant dosing with a histamine 2-receptor antagonist, could overcome these genetics-related differences in therapeutic effectiveness. For attaining higher eradication rates, the tailored regimen based on the relevant pharmacogenomics is preferable.

Genetic polymorphism of cytochrome P450s and P-glycoprotein in the Finnish population

The objective of this study was to investigate the genetic polymorphism of selected cytochrome P450 (CYP) enzymes and ABCB1 (encoding P-glycoprotein) of central importance with regard to the disposition of clinically used drugs in the Finnish population and to compare the results to pre-existing data from Caucasian populations. A random sample of 449 Finns was studied. Single nucleotide polymorphisms (SNPs) were genotyped using blood-derived genomic DNA and 5'-nuclease assays. We found that the allele frequencies of CYP1A2 SNP g.-163C>A, CYP2C8*3, CYP2C9*2, CYP2C9*3 and CYP2C19*2 were similar to those seen in other Caucasian populations. However, the allelic frequency of the variant ABCB1 SNP c.3435C>T allele was lower than previously reported. The frequency of the homozygous CYP3A5*1 expression was significantly higher than expected based on Hardy-Weinberg calculations (observed n = 8 vs. expected n = 3, P = 0.01). Other genotype frequencies corresponded to the expected values. The strong linkage between the CYP2C8*3 and the CYP2C9*2 alleles was confirmed in this study and the number of individuals with the rare haplotype CYP2C8*3*3/CYP2C9*2*2 was higher than expected. We conclude that the frequency of mutated CYP alleles in Finns were in agreement with earlier findings in Caucasian populations, but a lower frequency of the ABCB1 variant allele 3435T corresponding to that reported in Asian populations was found. The higher than expected frequency of the CYP3A5*1*1 genotype and the CYP2C8*3*3/CYP2C9*2*2 haplotype may influence the response to treatment with drugs metabolized by these enzymes.

Influence of cytochrome P450 polymorphisms on drug therapies: pharmacogenetic, pharmacoepigenetic and clinical aspects

The polymorphic nature of the cytochrome P450 (CYP) genes affects individual drug response and adverse reactions to a great extent. This variation includes copy number variants (CNV), missense mutations, insertions and deletions, and mutations affecting gene expression and activity of mainly CYP2A6, CYP2B6, CYP2C9, CYP2C19 and CYP2D6, which have been extensively studied and well characterized. CYP1A2 and CYP3A4 expression varies significantly, and the cause has been suggested to be mainly of genetic origin but the exact molecular basis remains unknown. We present a review of the major polymorphic CYP alleles and conclude that this variability is of greatest importance for treatment with several antidepressants, antipsychotics, antiulcer drugs, anti-HIV drugs, anticoagulants, antidiabetics and the anticancer drug tamoxifen. We also present tables illustrating the relative importance of specific common CYP alleles for the extent of enzyme functionality. The field of pharmacoepigenetics has just opened, and we present recent examples wherein gene methylation influences the expression of CYP. In addition microRNA (miRNA) regulation of P450 has been described. Furthermore, this review updates the field with respect to regulatory initiatives and experience of predictive pharmacogenetic investigations in the clinics. It is concluded that the pharmacogenetic knowledge regarding CYP polymorphism now developed to a stage where it can be implemented in drug development and in clinical routine for specific drug treatments, thereby improving the drug response and reducing costs for drug treatment.

Estimation of CYP2C19 activity by the omeprazole hydroxylation index at a single point in time after intravenous and oral administration

OBJECTIVE

The purpose of this study was to identify the common time point to achieve hydroxylation index (HI: omeprazole plasma concentration/5-hydroxyomeprazole plasma concentration) reflecting AUCOPZ/AUC5OH-OPZ after intravenous (IV) and oral (PO) administration.

METHODS

Twenty young and 28 elderly healthy subjects, including different CYP2C19 genotypes, were enrolled in the study. The young subjects received either 40 mg PO or 20 mg IV omeprazole, whereas the elderly subjects received 10 mg IV. The relation between AUCOPZ/AUC5OH-OPZ and HI was determined by Spearman's rank correlation. Multiple stepwise linear regression analysis was performed to identify the common time point to calculate HI that reflects AUCOPZ/AUC5OH-OPZ after IV.

RESULTS

In the correlation between HI and AUCOPZ/AUC5OH-OPZ IV at observed time points, HI3h showed the highest correlation coefficients (r = 0.894, p < 0.001) in all 48 subjects. The correlation of HI between IV and PO at observed time points showed that HI3h was highest (r = 0.916, p < 0.001) in 20 young subjects. Additionally, there was no significant difference between HI(3h) of IV and that of PO (12.9 +/- 15.9 and 12.9 +/- 15.1, p = 0.997). The regression equation of HI3h was the best to estimate AUCOPZ/AUC5OH-OPZ (AUCOPZ/AUC5OH-OPZ = 1.37 * HI3h + 0.18 * Age - 7.83, r2 = 0.883, p < 0.001).

CONCLUSIONS

This study demonstrated that HI3h after omeprazole IV was able to estimate AUCOPZ/AUC5OH-OPZ, as well as HI3h after PO. Additionally, CYP2C19 activity can be estimated more definitely by using HI after omeprazole IV without intestinal absorption.

Analytical methodologies for the determination of omeprazole: An overview

Omeprazole, a gastric acid pump inhibitor, dose-dependently controls gastric acid secretion; the drug has greater antisecretory activity than histamine H(2)-receptor antagonists. Omeprazole has been determined in formulations and biological fluids by a variety of methods such as spectrophotometry, high-performance liquid chromatography with ultraviolet detection and liquid chromatography coupled with tandem mass spectrometry. The overview includes the most relevant analytical methodologies used in its determination since the origin still today.

The impact of CYP allelic variation on antidepressant metabolism: a review

Psychiatric diseases that are treated with antidepressants are the leading causes of morbidity and mortality in humankind. Although antidepressants are generally well tolerated and widely available, they are not equally effective in all patients and only 35 - 45% of patients treated for depression with these drugs recover to premorbid levels of functioning. There is a need for an effective, individualized approach to antidepressant selection. One promising lead in the development of personalized medicine is the emerging field of pharmacogenomics, whereby pharmacologic agents are selected on the basis of the genotype of patients, with particular attention to drug targets and phase I- and phase II-metabolizing enzymes. This review article focuses on phase I antidepressant-metabolizing enzymes (e.g., relevant CYP enzymes). The authors first briefly review CYP nomenclature, the relevant members of the CYP superfamily and their alleles, the metabolic categories and CYP antidepressant substrates, inhibitors and inducers. The literature on the impact of CYP polymorphisms on antidepressant metabolism are also reviewed.

Pharmacogenomics-based tailored versus standard therapeutic regimen for eradication of H. pylori

Helicobacter pylori eradication rates by triple therapy with a proton pump inhibitor, amoxicillin, and clarithromycin at standard doses depend on bacterial susceptibility to clarithromycin and patient CYP2C19 genotypes. We examined the usefulness of a personalized therapy for H. pylori infection based on these factors as determined by genetic testing. First, optimal lansoprazole dosing schedules that would achieve sufficient acid inhibition to allow H. pylori eradication therapy in each of different CYP2C19 genotype groups were determined by a 24-h intragastric pH monitoring. Next, 300 H. pylori-positive patients were randomly assigned to the standard regimen group (lansoprazole 30 mg twice daily (b.i.d.)), clarithromycin 400 mg b.i.d., and amoxicillin 750 mg b.i.d. for 1 week) or the tailored regimen group based on CYP2C19 status and bacterial susceptibility to clarithromycin assessed by genetic testing. Patients with failure of eradication underwent the second-line regimen. The per-patient cost required for successful eradication was calculated for each of the groups. In the first-line therapy, the intention-to-treat eradication rate in the tailored regimen group was 96.0% (95% CI=91.5-98.2%, 144/150), significantly higher than that in the standard regimen group (70.0%: 95% CI=62.2-77.2%, 105/150) (P<0.001). Final costs per successful eradication in the tailored and standard regimen groups were $669 and $657, respectively. In conclusion, the pharmacogenomics-based tailored treatment for H. pylori infection allowed a higher eradication rate by the initial treatment without an increase of the final per-patient cost for successful eradication. However, the precise cost-effectiveness of this strategy remains to be determined.

Effect of Honey on CYP3A4, CYP2D6 and CYP2C19 Enzyme Activity in Healthy Human Volunteers

Honey is a common food supplement but not many studies have studied honey and drug interaction. This study investigates the influence of 7 days of honey administration on the activity of CYP3A4, CYP2D6 and CYP2C19 drug-metabolizing enzymes in healthy volunteers by using appropriate biomarker and probe drugs. A within-group pharmacokinetic study was done in 12 healthy volunteers. Urine samples (0-8 hr) were collected after administration of 30 mg of oral dextromethorphan (probe drug for CYP2D6) for analysis of dextromethorphan and dextrorphan. A plasma sample (4 hr) was collected after administration of 200 mg of oral proguanil (probe drug for CYP2C19) for the analysis of proguanil and cycloguanil. Urine samples (0-24 hr) were collected for the analysis of 6beta-hydroxycortisol (biomarker for CYP3A4). The volunteers were administered honey for 7 days. Subsequently blood and urine samples were collected after drug dosing as before. These samples were analysed for drug and metabolite concentrations in urine and plasma using high performance liquid chromatography method. Seven days of honey administration resulted in statistically significant increase in 24-hr urinary excretion of 6beta-hydroxycortisol. However, the metabolic ratios of dextromethorphan and proguanil were not significantly altered after 7 days of honey administration. Honey obtained from Western Ghats of southern India may induce CYP3A4 enzyme activity but not CYP2D6 and CYP2C19 enzyme activities.

Development of the “Inje Cocktail” for High-throughput Evaluation of Five Human Cytochrome P450 Isoforms in vivo

To develop and validate an in vivo cocktail method for high-throughput phenotyping of CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A, 12 healthy subjects received five probe drugs alone or simultaneously. The in vivo phenotyping index of CYP2C9, the ratio of 8 h urine concentration of losartan to its metabolite after a single administration of losartan, was not significantly different from that obtained using the five-drug cocktail. Similarly, the ratios of [omeprazole]/[5-hydroxyomeprazole] (CYP2C19) and [paraxanthine]/[caffeine] (CYP1A2) in 4 h plasma samples and the log ratio of [dextromethorphan]/[dextrorphan] (CYP2D6) in 8 h urine samples and the 4 h plasma concentrations of midazolam (CYP3A) after single administration or well-established three-drug cocktail of caffeine, omeprazole, and dextromethorphan were not significantly different from those after the new five-drug cocktail. In conclusion, the new five-drug cocktail regimen, named the "Inje cocktail," can be used as a tool to phenotype in vivo enzyme activities of CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A with only 4 h blood sampling and 8 h urine collection following simultaneous administration of the five probe drugs.

GENETIC POLYMORPHISMS OF CYTOCHROME P450 ENZYMES 2C9 AND 2C19 IN A HEALTHY IRANIAN POPULATION

1. The genetically polymorphic cytochrome P450 enzymes 2C9 (CYP2C9) and 2C19 (CYP2C19) are involved in the metabolism and elimination of a number of widely used drugs. The polymorphisms give rise to substantial interindividual and interethnic variability in drug excretion rates and final serum concentrations. For this reason, therapeutic responses and adverse drug reactions may vary from one person to another. In the present study we determined CYP2C9 and CYP2C19 genotypes in a random Iranian population to compare allele frequencies with previous findings in other ethnic groups. 2. Allelic variants of CYP2C9 (*1/*2/*3) and CYP2C19 (*1/*2/*3) were determined in 200 unrelated healthy Iranian volunteers by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays. 3. Fifteen subjects (7.5%) were homozygous for the CYP2C9*2 allele, whereas 21 individuals (10.5%) were heterozygous for this allele and 164 subjects (82%) had the wild-type allele (CYP2C9*1). No CYP2C9*3 was detected in the population sampled. Six subjects (3%) were homozygous for CYP2C19*2, whereas 44 individuals (22%) were heterozygous for this allele. In the remaining subjects (75%), no CYP2C19*2 was found. In addition, no CYP2C19*3 was detected in the population sampled. 4. Based on our data, the frequency of the CYP2C9*2 allelic variant in Iranians is similar to that in other Caucasian populations; however, the frequency of the CYP2C9*3 allele differed significantly (P < 0.05). Conversely, there was no difference in the frequency of CYP2C19 allelic variants between the present study and other studies evaluating this allele in Caucasian populations (P > 0.05).

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

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.

Amodiaquine, its desethylated metabolite, or both, inhibit the metabolism of debrisoquine (CYP2D6) and losartan (CYP2C9) in vivo

OBJECTIVE

To study the extent of in vivo inhibition by the antimalarial drug amodiaquine, its active metabolite N-desethylamodiaquine, or both, of the metabolism of four probe drugs of the enzymes CYP2D6, CYP2C19, CYP2C9 and CYP1A2.

METHODS

Twelve healthy Swedish volunteers received a cocktail of four probe drugs (debrisoquine, omeprazole, losartan and caffeine) to determine their baseline metabolic capacities. After a washout period, they received a 600 mg oral dose of amodiaquine hydrochloride; and 2-3 h later the cocktail was administered again. One week after the intake of amodiaquine, the subjects received the cocktail a third time. The levels of probe drugs and their metabolites as well as amodiaquine and its metabolite were determined by HPLC.

RESULTS

Plasma levels of amodiaquine and N-desethylamodiaquine could be followed in all subjects for 6 h and 28 days, respectively. Among the 12 subjects, a 3-fold variation in amodiaquine AUC and a 2-fold variation in N-desethylamodiaquine AUC, were observed. The CYP2D6 and CYP2C9 activities of the subjects were measured by debrisoquine and losartan phenotyping tests, respectively. There were significant mean increases in debrisoquine metabolic ratio (MR) between baseline and the second cocktail [MR(2 h)-MR(baseline) 1.426 (95% confidence interval 1.159, 1.755), P=0.002; ANOVA, Fisher LSD test] and in mean losartan MR between baseline and the second cocktail [MR(2 h)-MR(baseline) 1.724 (95% confidence interval 1.076, 2.762), P=0.026; ANOVA, Fisher LSD test]. The effects on CYP2D6 and CYP2C9 activities subsided within a week after intake of amodiaquine as tested by the phenotyping cocktail. The changes in omeprazole MRs and caffeine MRs were not statistically significant between any of the study phases.

CONCLUSION

A single dose of amodiaquine decreased CYP2D6 and CYP2C9 activities significantly compared to baseline values. Amodiaquine has the potential to cause drug-drug interactions and should be further investigated in malarial patients treated with drug combinations containing amodiaquine.

In vivo metabolic activity of CYP2C19 and CYP3A in relation to CYP2C19 genetic polymorphism in chronic liver disease

To study whether chronic liver disease (CLD) and genetic polymorphism affect the hepatic activity of cytochrome P450 (CYP) isoforms, we compared in vivo CYP2C19 and CYP3A activities using 3-hour omeprazole hydroxylation index (plasma concentration ratio of omeprazole to its 5-hydroxylated metabolite; a higher index indicates lower CYP2C19 activity) and partial formation clearance of cortisol to 6beta-hydroxycortisol (CL(cortisol-->6beta-HC)) in 31 CLD patients (9 with chronic hepatitis; 22 with cirrhosis comprising 20 Child-Pugh type A, 1 type B, and 1 type C) and 30 healthy subjects with different CYP2C19 genotypes. The mean (+/-SEM) omeprazole hydroxylation index in CLD patients with homozygous extensive metabolizer (EM) genotype (*1/*1, n = 8), heterozyous EM (*1/*2, n = 11; *1/*3, n = 6) genotypes and poor metabolizer (PM) genotypes (*2/*2, n = 3; *3/*3, n = 3) were 17.15 +/- 2.12, 20.02 +/- 2.63, and 26.04 +/- 3.15, respectively, which were significantly higher compared with control subjects with the corresponding CYP2C19 genotypes (0.81 +/- 0.09, 1.55 +/- 0.20, and 15.5 +/- 1.52). CLD patients with PM genotype had significantly (P < .05) higher omeprazole hydroxylation indexes than did those with homozygous EM genotype, and those with heterozygous EM genotypes had intermediate values. The mean CL(cortisol-->6beta-HC) decreased significantly (P < .001) in CLD patients compared with control subjects (1.19 +/- 0.12 versus 2.26 +/- 0.24 mL/min). Multiple regression analysis showed that CLD, serum albumin level, and CYP2C19 genotype correlated significantly (P < .05) with the omeprazole hydroxylation index, whereas no significant correlation was observed between CL(cortisol-->6beta-HC) and other variables, except CLD. Because CLD and genetic polymorphism of CYP2C19 act additively to reduce CYP2C19 activity, genotyping these patients may be of value in averting adverse reactions of drugs that depend on CYP2C19 for elimination.

Risk factors for extrapyramidal symptoms during treatment with selective serotonin reuptake inhibitors, including cytochrome P-450 enzyme, and serotonin and dopamine transporter and receptor polymorphisms

INTRODUCTION

Extrapyramidal symptoms (EPS) are rare adverse drug reactions to selective serotonin reuptake inhibitors (SSRIs). This study aimed to investigate the potential risk factors for EPS associated with SSRIs including polymorphisms of cytochrome P-450 isoenzymes, and serotonin and dopamine transporters and receptors.

METHODS

All spontaneous adverse drug reaction reports received by the Swedish Medical Products Agency until December 1999 that were coded with EPS and judged to be at least possibly related to SSRI treatment were included in the study. Reporting physicians received a form for collection of relevant information including current and previous use of SSRIs and antipsychotics, alcohol or substance abuse, central nervous system damage, a history of epilepsy or EPS, and a family history of Parkinson disease. A blood sample was also requested for genotyping of selected cytochrome P-450, and serotonin and dopamine transporter and receptor mutations.

RESULTS

A total of 64 cases of EPS were reported. Twenty-eight forms (46%) were returned, and 20 blood samples were obtained. Identified potential risk factors included age of 65 years or older and the presence of the A1 allele of the D2 dopamine receptor gene (DRD2) Taq1A polymorphism (relative risk, 2.4; 95% confidence interval, 1.2-4.5 vs literature controls). No relationship was apparent for sex, drug dose, or other genetic polymorphisms. At least 1 additional potential risk factor for EPS, such as a history of central nervous system damage, alcohol or substance abuse, epilepsy, Parkinson disease, previous or current exposure to antipsychotic drugs, concomitant treatment with other antidopaminergic or serotonergic agents, or a history of EPS, was found in 93% of the cases.

CONCLUSION

The risk of EPS with SSRIs seems to increase with advanced age and with the presence of the A1 allele of DRD2 Taq1A polymorphism. Because of the small sample size of our study and the use of historical controls rather than patients who did not experience EPS during SSRIs treatment, the DRD2 finding is preliminary and needs to be replicated in other studies before firm conclusions can be drawn. At least 1 additional potential risk factor was found in almost all cases.

The effect of aging on the relationship between the cytochrome P450 2C19 genotype and omeprazole pharmacokinetics

BACKGROUND AND OBJECTIVE

The metabolic activity of cytochrome P450 (CYP) 2C19 is genetically determined, and the pharmacokinetics of omeprazole, a substrate for CYP2C19, are dependent on the CYP2C19 genotype. However, a discrepancy between the CYP2C19 genotype and omeprazole pharmacokinetics was reported in patients with liver disease or advanced cancer. The objective of the present study was to evaluate the effect of aging on the relationship between the CYP2C19 genotype and its phenotype.

METHODS

Twenty-eight elderly and 23 young Japanese volunteers were enrolled after being genotyped. Each subject received a single intravenous dose of omeprazole (10 mg and 20 mg for the elderly and the young groups, respectively) and blood samples were obtained up to 6 hours after dose administration to determine the plasma concentrations of omeprazole and its metabolites, 5-hydroxyomeprazole and omeprazole sulfone. Pharmacokinetic parameters were obtained by noncompartmental analysis. Linear regression models were used to examine the joint effects of covariates such as genotype, age, etc., on the pharmacokinetic parameters, and the pharmacokinetic parameters showing statistical significance were compared by ANOVA.

RESULTS

There were significant differences between genotypes in the area under the plasma concentration-time curve of the young group and the elderly group. The number of mutation alleles and age were significant covariates for systemic clearance (CL), but age was the only significant covariate for volume of distribution at steady state (Vss). There were significant age- and genotype-related differences and a significant age x genotype interaction in CL (20.6+/-11.0/12.7+/-4.0/3.2+/-1.0 and 5.4+/-4.0/3.7+/-1.4/2.1+/-0.7 L/h for homozygous extensive metabolisers [EMs]/heterozygous EMs/poor metabolisers [PMs] of the young and the elderly groups, respectively). In Vss, a significant difference was found between the young and the elderly groups (219+/-115 and 107+/-44.5 mL/kg, respectively), but not between three genotypes (178+/-142, 173+/-79 and 110+/-51 mL/kg for homozygous EMs, heterozygous EMs and PMs, respectively).

CONCLUSION

The elderly EMs showed wide variance in the in vivo CYP2C19 activity and were phenotypically closer to the elderly PMs than the young EMs were to the young PMs. Some of the elderly homozygous EMs, as well as heterozygous EMs, have a metabolic activity similar to PMs, and the CYP2C19 genotype may therefore not be as useful as phenotyping in the elderly.

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.

Metabolic Ratios of Psychotropics as Indication of Cytochrome P450 2D6/2C19 Genotype

The cytochrome P450 enzymes (CYP) 2C19 and 2D6 are involved in the metabolism of many psychotropic drugs. Variability in enzyme activity results in variable metabolic capacities, affecting the metabolism of substrates. The metabolic ratio (MR) of drugs metabolized via these enzymes may therefore reflect the enzyme's activity and/or genotype. To serve as an example for different groups of medications, the selective serotonin reuptake inhibitor venlafaxine, the tricyclic antidepressant amitriptyline, and the antipsychotic risperidone were studied to examine a possible correlation between the MRs of these drugs and the CYP2C19 and/or CYP2D6 genotype. For this purpose data from routine genotyping and serum level analysis were used. The relationships between the observed metabolic ratios and CYP2D6 and/or CYP2C19 genotype were characterized using nonparametric statistical analysis. A clear correlation was observed between the CYP2D6 genotype and the metabolic ratio of venlafaxine. Genotyping of individuals with a log(MR) < -0.6 or a log(MR) > 0.2 would include all patients with an aberrant genotype but would result in a reduction of 52% of genotyping reactions. Slow metabolism of amitriptyline is correlated with a log(MR) > 0.4. Genotyping only those subjects with a log(MR) > 0.4 would result in 88% fewer genotyping reactions. For risperidone, genotyping individuals with a log(MR) > 0.4 would include all CYP2D6 poor metabolizers while reducing the number of genotyping reactions by 93%. According to these data, correlations exist between the log(MR) of venlafaxine, amitriptyline, and risperidone and the genotype of the CYP enzymes involved in their metabolism. From the ranges of log(MR) defined here, a high percentage of aberrant metabolizers can be detected even when patients are not routinely genotyped. Thus, the metabolic ratio may serve as an indication of when genotyping should be considered.

Genetic polymorphism of CYP2C9 and CYP2C19 in a Bolivian population: an investigative and comparative study

OBJECTIVE

Several reports of CYP2C genetic polymorphism demonstrate its potential clinical role in determining both inter-individual and inter-ethnic differences in drug efficacy. We estimated the distribution of CYP2C9 and CYP2C19 common variants in the Bolivian population (a South American population), and compared these data with those from Asian, African, Caucasian and Oceanian populations.

METHODS

Genomic DNA was obtained from 778 unrelated healthy volunteers from Bolivia. The genotypic status of CYP2C9 and CYP2C19 was determined by means of polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Allelic and genotypic frequencies of CYP2C9 and CYP2C19 were determined for the Bolivian population, and comparison of the data with other ethnic groups revealed a lower CYP2C9*2 frequency (4.8%) than in Caucasians, but a higher frequency than in Asians; frequencies of CYP2C9*3 (3.0%) and CYP2C9 (0.4%) poor metabolizers (PMs) were similar to those seen in Asian populations. Frequencies of CYP2C19*2 (7.8%), CYP2C19*3 (0.1%), and CYP2C19 PMs (1.0%) in the Bolivian population were for the most part lower than in Caucasian, Asian, Oceanian and African populations.

CONCLUSION

This is the first study to investigate a South American population for genetic polymorphism in the CYP2C subfamily. The Bolivian population differs from most other ethnic groups in the incidence of CYP2C9 and CYP2C19 common variants that might be influenced by its admixture characteristics.

Lack of weight-based dose dependency and intraindividual variability of omeprazole for CYP2C19 phenotyping

To determine if dose dependency occurs with 2 weight-based single doses of omeprazole in a phenotyping study, as well as to quantitate 3-month intraindividual variability of CYP2C19 activity, 24 Caucasian subjects with body weights from 45 to 66 kg and 67 to 90 kg received single oral 30-mg and 40-mg doses of omeprazole, respectively. Female subjects were phenotyped during the mid-follicular and mid-luteal phases of their menstrual cycles for 3 complete cycles. Male subjects were phenotyped every 14 days for 12 weeks. Subjects with a body weight between 45 and 66 kg received an additional 40-mg omeprazole single dose on visit 7. The 2-hour postdose plasma concentration ratio of omeprazole to 5-hydroxyomeprazole was used as a measure of CYP2C19 activity. The percent coefficient of variation (CV%) of omeprazole phenotyping ranged from 6.3% to 51.3% (median = 18.5%, interquartile range = 14.8%-23.5%). Weight-based single doses of omeprazole for CYP2C19 phenotyping did not exhibit dose dependency. Therefore, a weight-based approach may improve the quantitation of omeprazole/metabolites.

Omeprazole as a CYP2C19 marker in Chinese subjects: assessment of its gene-dose effect and intrasubject variability

The objective of this study was to determine the reliability of omeprazole as a marker for CYP2C19 activity in Chinese subjects. In 27 healthy male Chinese subjects, the CYP2C19 phenotype was first determined with the standard mephenytoin hydroxylation index (HI) method. Subsequently, the subjects were randomized in a three-way crossover manner to receive an oral 40-mg dose from each of three omeprazole formulations (as part of a bioequivalence study). Multiple blood samples were obtained over 12 hours, and plasma concentrations of omeprazole, 5-hydroxyomeprazole, and omeprazole sulfone were determined by a high-performance liquid chromatography (HPLC) method. Individual CYP2C19 genotype was determined by the polymerase chain reaction/restriction fragment length polymorphism method. To assess the specificity for CYP2C19 activity, the hydroxylation metabolic ratio (MR) of omeprazole (AUC(omeprazole)/AUC(5-hydroxyomeprazole)) was compared to mephenytoin HI and related to CYP2C19 genotype status. The inter- and intrasubject variabilities of MR were also calculated, and their magnitudes were compared. The intersubject MR varied more than 20 fold. Among the subjects, there was a gene-dose effect, and the mean MR was 1.76, 3.45, and 33.08, respectively, in the homozygous extensive metabolizers (wt/wt, n = 9), heterozygous extensive metabolizers (wt/m1 or wt/m2, n = 10), and poor metabolizers (m1/m1 or m1/m2, n = 7). However, the coefficients of variation for intrasubject MR only ranged from 4.5% to 33.7% over the three periods with the three formulations. The phenotype based on MR was concordant with HI. In view of the clear gene-dose effect, concordance with mephenytoin HI, and low intrasubject variability, omeprazole MR following a 40-mg oral dose can be considered as a specific and sensitive marker for CYP2C19 activity in Chinese subjects.

Enantiomeric determination of the plasma levels of omeprazole by direct plasma injection using high-performance liquid chromatography with achiral-chiral column-switching

A direct injection high-performance liquid chromatographic (HPLC) method, with column-switching, for the determination of omeprazole enantiomers in human plasma is described. A restricted access media (RAM) of bovine serum albumin (BSA) octyl column has been used in the first dimension for separation of the analyte from the biological matrix. The omeprazole enantiomers were eluted from the RAM column onto an amylose tris(3,5-dimethylphenylcarbamate) chiral column by the use of a column-switching valve and the enantioseparation was performed using acetonitrile-water (60:40 v/v) as eluent. The analytes were detected by their UV absorbance at 302 nm. The validated method was applied to the analysis of the plasma samples obtained from 10 Brazilian volunteers who received a 40 mg oral dose of racemic omeprazole and was able to quantify the enantiomers of omeprazole in the clinical samples analyzed. The assay was able to determine the cytochrome P450 2C19 phenotype of the subjects participating in this study.

Induction of Testosterone Metabolism by Esomeprazole in aCYP2C19*2 Heterozygote

The authors describe a 42-year-old woman with previously normal sexual function who gradually developed loss of libido during treatment with esomeprazole. While taking esomeprazole, the patient's loss of libido improved with oral testosterone supplementation and deteriorated after testosterone withdrawal. There was steady improvement in both sexual function and serum free testosterone concentration after discontinuation of esomeprazole. Due to the temporal relationship between esomeprazole intake and sexual dysfunction, the authors postulate that esomeprazole causes induction of testosterone metabolism. The authors believe this to be the first case of female sexual dysfunction associated with esomeprazole described in the literature. They discuss a number of possible mechanisms for this effect.

Polymorphism of interleukin-1beta affects the eradication rates of Helicobacter pylori by triple therapy

BACKGROUND AND AIMS

Polymorphism in interleukin-1beta (IL-1beta) is associated with intragastric pH levels in Helicobacter pylori-positive subjects. Intragastric pH levels affect the activity of antibiotics against H. pylori in the stomach. The aim of this study was to investigate whether IL-1beta polymorphism is associated with eradication rates of H. pylori by triple therapy with a proton pump inhibitor (PPI), amoxicillin, and clarithromycin.

METHODS

Three hundred thirty-six patients infected with H. pylori completed treatment with omeprazole, 20 mg, or lansoprazole, 30 mg twice daily; clarithromycin, 200 mg 3 times daily; and amoxicillin, 500 mg 3 times daily, for 1 week. IL-1beta-511 and CYP2C19 genotypes of patients and sensitivity of H. pylori to clarithromycin and amoxicillin were determined.

RESULTS

Logistic regression analysis showed that the IL-1beta-511 polymorphism, as well as CYP2C19 genotype of patients and clarithromycin-resistance of H. pylori, was associated with successful eradication. Eradication rates for H. pylori were 77.3% (75 of 97; 95% confidence interval, 67.5-84.6), 89.6% (147 of 164; 95% confidence interval, 83.9-93.1), and 94.7% (95% confidence interval, 86.9-98.5) in patients with the C/C, C/T, and T/T genotypes of IL-1beta-511, respectively (P = 0.0014).

CONCLUSIONS

IL-1beta-511 polymorphism is one of the determinants of successful eradication of H. pylori using triple therapy with a PPI, amoxicillin, and clarithromycin, together with CYP2C19 genotype and bacterial resistance to clarithromycin.

Development of analytical technology in pharmacogenetic research

Methods used to determine phenotype and genotype for pharmacogenetic polymorphisms are discussed. Phenotyping is mainly applicable to polymorphisms affecting drug disposition rather than drug response and can involve either direct measurement of enzyme activity or administration of a probe drug followed by measurement of drug and/or metabolite levels. Genotyping is now more widely used than phenotyping and can be used to determine genotype for polymorphisms affecting either drug disposition (for example those in the cytochromes P450 or N-acetyltransferases) or drug response (for example those in drug receptors). Most genotyping for known polymorphisms involves use of the polymerase chain reaction and the wide variety of methods based on this technique that are now used for routine genotyping are discussed in detail. In addition, a range of methods that can be used to detect novel polymorphisms, thereby further increasing understanding of interindividual variability in drug disposition and response, is described.

The effect of ethinyloestradiol and levonorgestrel on the CYP2C19-mediated metabolism of omeprazole in healthy female subjects

AIMS

To study the effect of an oral contraceptive (OC) formulation containing ethinyloestradiol and levonorgestrel (LNG) (combination OC) or LNG alone on the CYP2C19-mediated hydroxylation of omeprazole in healthy females.

METHODS

This was an open crossover study with three phases. In phase one, 10 healthy females received a single 40-mg dose of omeprazole. Thereafter the subjects received in a random order either 40 micro g ethinyloestradiol and 75 micro g LNG or 60 micro g LNG alone once daily for 10 days. On day 10, 1 h after the last OC dose, subjects received a single 40-mg oral dose of omeprazole. The plasma concentrations of omeprazole, 5'-hydroxyomeprazole and omeprazole sulphone were determined for up to 8 h.

RESULTS

The use of combination OC increased the area under the curve (AUC) of omeprazole by 38% [95% confidence interval (CI) - 3.8, 80; P = 0.040] and caused a 48% increase (95% CI 28, 68) in the AUC ratio of omeprazole/5-hydroxyomeprazole. LNG alone did not effect the 5'-hydroxylation of omeprazole. Neither of the OC preparations seemed to have an inhibitory effect on the formation of omeprazole sulphone by CYP3A4.

CONCLUSIONS

Oral contraceptives containing ethinyloestradiol but not those containing only LNG decrease CYP2C19 activity.

Simultaneous enantiospecific separation and quantitation of mephenytoin and its metabolites nirvanol and 4'-hydroxymephenytoin in human plasma by liquid chromatography

A high-performance liquid chromatographic method for the enantiospecific quantitation of S- and R-mephenytoin and its metabolites S- and R-nirvanol and S- and R-4'-hydroxymephenytoin in plasma is described. The compounds were separated using a reversed-phase C(2) column in tandem with a chiral alpha(1)-acid glycoprotein column and were detected using ultraviolet detection at 205 nm. The lower limit of quantification was 10 ng/ml for all compounds using 0.5 ml human plasma (intra-day coefficient of variation <13%, accuracy <+/-20%). The method was validated for human plasma in the concentration range 10-2000 ng/ml for each of the six compounds. The method allows for the simultaneous characterisation of the metabolic capacity of two human drug-metabolising enzymes, CYP2C19 and CYP2B6, and may be used when investigating polymorphisms or changes in activity of these two enzymes.

The conduct of in vitro and in vivo drug-drug interaction studies: a Pharmaceutical Research and Manufacturers of America (PhRMA) perspective

Current regulatory guidances do not address specific study designs for in vitro and in vivo drug-drug interaction studies. There is a common desire by regulatory authorities and by industry sponsors to harmonize approaches, to allow for a better assessment of the significance of findings across different studies and drugs. There is also a growing consensus for the standardization of cytochrome P450 (P450) probe substrates, inhibitors and inducers and for the development of classification systems to improve the communication of risk to health care providers and to patients. While existing guidances cover mainly P450-mediated drug interactions, the importance of other mechanisms, such as transporters, has been recognized more recently, and should also be addressed. This article was prepared by the Pharmaceutical Research and Manufacturers of America (PhRMA) Drug Metabolism and Clinical Pharmacology Technical Working Groups and represents the current industry position. The intent is to define a minimal best practice for in vitro and in vivo pharmacokinetic drug-drug interaction studies targeted to development (not discovery support) and to define a data package that can be expected by regulatory agencies in compound registration dossiers.