Miotic action of tramadol is determined by CYP2D6 genotype

Polymorphic CYP2D6 is the enzyme that activates the opioid analgesic tramadol by O-demethylation to its active metabolite O-demethyltramadol (M1). Our objective was to determine the opioid effects measured by pupillary response to tramadol of CYP2D6 genotyped volunteers in relation to the disposition of tramadol and M1 in plasma. Tramadol displayed phenotypic pharmacokinetics and it was possible to identify poor metabolizers (PM) with >99% confidence from the metabolic ratio (MR) in a single blood sample taken between 2.5 and 24 h post-dose. Homozygous extensive metabolizers (EM) differed from PM subjects by an almost threefold greater (P=0.0014) maximal pupillary constriction (Emax). Significant correlations between the AUC and Cmax values of M1 versus pupillary constriction were found. The corresponding correlations of pharmacokinetic parameters for tramadol itself were weaker and negative. The strongest correlations were for the single-point metabolic ratios at all sampling intervals versus the effects, with rs ranging from 0.85 to 0.89 (p<0.01). It is concluded that the concept of dual opioid/non-opioid action of the drug, though considerably stronger in EMs, is valid for both EM and PM subjects. This is the theoretical basis for the frequent use and satisfactory efficacy of tramadol in clinical practice when given to genetically non-selected population.     

Automated determination of tramadol enantiomers in human plasma using solid-phase extraction in combination with chiral liquid chromatography

A sensitive and automated method for the separation and individual determination of tramadol enantiomers in plasma has been developed using solid-phase extraction (SPE) on disposable extraction cartridges (DECs) in combination with chiral liquid chromatography (LC). The SPE operations were performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with ethyl silica (50 mg) was first conditioned with methanol and phosphate buffer, pH 7.4 A 1.0-ml volume of plasma was then applied on the DEC. The washing step was performed with the same buffer. The analytes were eluted with 0.15 ml of methanol, and 0.35 ml of phosphate buffer, pH 6.0, containing sodium perchlorate (0.2 M) were added to the extract before injection into the LC system. The enantiomeric separation of tramadol was achieved using a Chiralcel OD-R column containing cellulose tris-(3,5-dimethylphenylcarbamate) as chiral stationary phase. The mobile phase was a mixture of phosphate buffer, pH 6.0, containing sodium perchlorate (0.2 M) and acetonitrile (75:25). The mobile-phase pH and the NaClO₄ concentration were optimized with respect to enantiomeric resolution. The method developed was validated. Recoveries for both enantiomers of tramadol were about 100%. The method was found to be linear in the 2.5–150 ng/ml concentration range [r²=0.999 for (+)- and (−)-tramadol]. The repeatability and intermediate precision at a concentration of 50 ng/ml were 6.5 and 8.7% for (+)-tramadol and 6.1 and 7.6% for (−)-tramadol, respectively.     

The AmpliChip CYP450 genotyping test: Integrating a new clinical tool

The AmpliChip CYP450 Test, which analyzes patient genotypes for cytochrome P450 (CYP) genes CYP2D6 and CYP2C19, is a major step toward introducing personalized prescribing into the clinical environment. Interest in adverse drug reactions (ADRs), the genetic revolution, and pharmacogenetics have converged with the introduction of this tool, which is anticipated to be the first of a new wave of such tools to follow over the next 5-10 years. The AmpliChip CYP450 Test is based on microarray technology, which combines hybridization in precise locations on a glass microarray and a fluorescent labeling system. It classifies individuals into two CYP2C19 phenotypes (extensive metabolizers [EMs] and poor metabolizers [PMs]) by testing three alleles, and into four CYP2D6 phenotypes (ultrarapid metabolizers [UMs], EMs, intermediate metabolizers [IMs], and PMs) by testing 27 alleles, including seven duplications. CYP2D6 is a metabolic enzyme with four activity levels (or phenotypes): UMs with unusually high activity; normal subjects, known as EMs; IMs with low activity; and PMs with no CYP2D6 activity (7% of Caucasians and 1-3% in other ethnic groups). Levels of evidence for the association between CYP2D6 PMs and ADRs are relatively reasonable and include systematic reviews of case-control studies of some typical antipsychotics and tricyclic antidepressants (TCAs). Evidence for other phenotypes is considerably more limited. The CYP2D6 PM phenotype may be associated with risperidone ADRs and discontinuation due to ADRs. Venlafaxine, aripiprazole, duloxetine, and atomoxetine are newer drugs metabolized by CYP2D6 but studies of the clinical relevance of CYP2D6 genotypes are needed. Non-psychiatric drugs metabolized by CYP2D6 include metoprolol, tamoxifen, and codeine-like drugs. CYP2C19 PMs (3-4% of Caucasians and African Americans, and 14-21% of Asians) may require dose adjustment for some TCAs, moclobemide, and citalopram. Other drugs metabolized by CYP2C19 are diazepam and omeprazole. The future of pharmacogenetics depends on the ability to overcome serious obstacles, including the difficulties of conducting and publishing studies in light of resistance from grant agencies, pharmaceutical companies, and some scientific reviewers. Assuming more studies are published, pharmacogenetic clinical applications may be compromised by economic factors and the lack of physician education. The combination of a US FDA-approved test, such as the AmpliChip CYP450 Test, and an FDA definition of CYP2D6 as a 'valid biomarker' makes CYP2D6 genotyping a prime candidate to be the first successful pharmacogenetic test in the clinical environment. One can use microarray technology to test for hundreds of single nucleotide polymorphisms (SNPs) but, taking into account the difficulties for single gene approaches such as CYP2D6, it is unlikely that very complex pharmacogenetic approaches will reach the clinical market in the next 5-10 years.     

Inhibitory Effects of the Monoamine Oxidase Inhibitor Tranylcypromine on the Cytochrome P450 Enzymes CYP2C19, CYP2C9, and CYP2D6

1. The inhibitory effects of tranylcypromine, a nonselective irreversible inhibitor of monoamine oxidase (MAO), on three cytochrome P450 (CYP) enzymes, namely CYP2C9, CYP2C19, and CYP2D6, have been evaluated in vitro. 2. The studies were conducted using cDNA-expressed human CYP enzymes and probe substrates. 3. A range of substrate concentrations was coincubated with a range of tranylcypromine concentrations in the presence of each of the CYP enzymes at 37 degrees C for a predetermined period of time. Product concentrations were quantified by HPLC with UV detection. 4. The results demonstrated that tranylcypromine is a competitive inhibitor of CYP2C19 (Ki = 32 microM) and CYP2D6 (Ki = 367 microM) and a noncompetitive inhibitor of CYP2C9 (Ki = 56 microM). 5. None of these inhibitory effects are considered clinically significant at usual therapeutic doses. However, in certain situations such as high dose tranylcypromine therapy, or in poor metabolizers of CYP2C19 substrates, clinically significant interactions might occur, particularly when tranylcypromine is coadministered with drugs with a narrow therapeutic index.     

Enantioselective analysis of unbound tramadol, O-desmethyltramadol and N-desmethyltramadol in plasma by ultrafiltration and LC-MS/MS: application to clinical pharmacokinetics

This study describes the enantioselective analysis of unbound and total concentrations of tramadol and its main metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2) in human plasma. Sample preparation was preceded by an ultrafiltration step to separate the unbound drug. Both the ultrafiltrate and plasma samples were submitted to liquid/liquid extraction with methyl t-butyl ether. Separation was performed on a Chiralpak(?) AD column and tandem mass spectrometry consisting of an electrospray ionization source, positive ion mode and multiple reaction monitoring was used as the detection system. Linearity was observed in the following ranges: 0.2-600 and 0.5-250 ng/mL for analysis of total and unbound concentrations of the tramadol enantiomers, respectively, and 0.1-300 and 0.25-125 ng/mL for total and unbound concentrations of the M1 and M2 enantiomers, respectively. The lower limits of quantitation were 0.2 and 0.5 ng/mL for analysis of total and unbound concentration of each tramadol enantiomer, respectively, and 0.1 and 0.25 ng/mL for total and unbound concentrations of M1 and M2 enantiomers, respectively. Intra- and interassay reproducibility and inaccuracy did not exceed 15%. Clinical application of the method to patients with neuropathic pain showed plasma accumulation of (+)-tramadol and (+)-M2 after a single oral dose of racemic tramadol. Fractions unbound of tramadol, M1 or M2 were not enantioselective in the patients investigated.     

Polymorphic Cytochromes P450 and Drugs Used in Psychiatry

1. The cytochrome P450 monooxygenases, CYP2D6, CYP2C19, and CYP2C9, display polymorphism. CYP2D6 and CYP2C19 have been studied extensively, and despite their low abundance in the liver, they catalyze the metabolism of many drugs.2. CYP2D6 has numerous allelic variants, whereas CYP2C19 has only two. Most variants are translated into inactive, truncated protein or fail to express protein.3. CYP2C9 is expressed as the wild-type enzyme and has two variants, in each of which one amino acid residue has been replaced.4. The nucleotide base sequences of the cDNAs of the three polymorphic genes and their variants have been determined, and the proteins derived from these genes have been characterized.5. An absence of CYP2D6 and/or CYP2C19 in an individual produces a poor metabolizer (PM) of drugs that are substrates of these enzymes.6. When two drugs that are substrates for a polymorphic CYP enzyme are administered concomitantly, each will compete for that enzyme and competitively inhibit the metabolism of the other substrate. This can result in toxicity.7. Patients can be readily phenotyped or genotyped to determine their CYP2D6 or CYP2C19 enzymatic status. Poor metabolizers (PMs), extensive metabolizers (EMs), and ultrarapid metabolizers (URMs) can be identified.8. Numerous substrates and inhibitors of CYP2D6, CYP2C19, and CYP2C9 are identified.9. An individual's diet and age can influence CYP enzyme activity.10. CYP2D6 polymorphism has been associated with the risk of onset of various illnesses, including cancer, schizophrenia, Parkinson's disease, Alzheimer's disease, and epilepsy.     

Designer drug 2,5-dimethoxy-4-methyl-amphetamine (DOM, STP): involvement of the cytochrome P450 isoenzymes in formation of its main metabolite and detection of the latter in rat urine as proof of a drug intake using gas chromatography-mass spectrometry

The designer drug 2,5-dimethoxy-4-methyl-amphetamine (DOM, STP) is known to be extensively metabolized in various species. The current study showed that cytochrome P450 2D6 was the only isoenzyme involved in formation of the main metabolite hydroxy DOM. In addition, the authors' systematic toxicological analysis (STA) procedure using full-scan GC-MS was suitable to prove an intake of a common drug users' dose of DOM by detection of hydroxy DOM in rat urine. Assuming similar metabolism, the described STA procedure should be suitable for proof of an intake of DOM in human urine. However, DOM and/or other metabolites such as deamino-oxo-hydroxy DOM might be the target analyte in urine of CYP2D6 poor metabolizers.     

Frequency of single nucleotide polymorphisms of CYP2D6 in the Czech population

CYP2D6 is a member of cytochrome P450 enzymes that metabolise over 25% of commonly used drugs. Genetic polymorphisms can cause insufficient drug efficacy at usually administered doses or can be the cause of adverse drug reaction. CYP2D6 genotyping can be used to predict CYP2D6 phenotype and thereby explain some abnormalities in drug response and thus optimize pharmacotherapy. The aim of this study was to investigate the frequency of functionally important variant alleles of the CYP2D6 gene throughout the Czech population to predict the prevalence of ultra-rapid and poor metabolizer phenotypes. The DNA of 223 unrelated, healthy volunteers was analysed to detect the presence of CYP2D6*6, *5, *4, *3 and gene duplication. The variant allele frequencies in our population were 0.22%, 3.14%, 22.87%, 1.12% and 3.14% for CYP2D6*6, CYP2D6*5, CYP2D6*4, CYP2D6*3 and CYP2D6*MxN, respectively. Fifteen subjects carried two variant alleles leading to predicted poor type of metabolism, 84 subjects were heterozygous extensive metabolizers (het-EM). The full-text contains detailed comparison with European white populations. The distribution of variant alleles complies with the Hardy-Weinberg equilibrium. The frequencies of functional variant alleles of CYP2D6 in Czech population are in concordance with other Caucasian populations.     

Development of a PCR-based strategy for CYP2D6 genotyping including gene multiplication of worldwide potential use

There is growing consensus on the potential use of pharmacogenetics in clinical practice, and hopes have been expressed for application to the improvement of global health. However, two major challenges may lead to widening the "biotechnological gap" between the developing and the industrial world;first the unaffordability of some current technologies for poorer countries, and second the necessity of analyzing all described alleles for every clinical case due to the inability to predict the ethnic group of a given patient. Because of its role in the metabolism of a number of drugs, cytochrome P450 2D6 (CYP2D6) is an excellent candidate for use in the optimization of drug therapy. CYP2D6 is a highly polymorphic gene locus with more than 50 variant alleles, and subjects can be classified as poor metabolizers (PM), extensive metabolizers (EM), or ultrarapid metabolizers (UM) of a given CYP2D6 substrate. Several strategies and methods for CYP2D6 genotyping exist. Some, however, are expensive and laborious. The aim of this study was to design a PCR-based genotyping methodology to allow rapid, straightforward, and inexpensive identification of 90%-95% of CYP2D6 PM or UM genotypes for routine clinical use, independent of the individual's ethnic group. CYP2D6 is amplified in initial extra long PCRs (XL-PCRs), which subsequently undergo fragment-length polymorphism analysis for the determination of carriers of CYP2D6 allelic variants. The same XL-PCRs are also used for the determination of CYP2D6 multiplication and 2D6*5 allele (abolished activity). The application of this new strategy for the detection of CYP2D6 mutated alleles and multiplications to routine clinical analysis will enable the PM and UM phenotypes to be predicted and identified at a reasonable cost in a large number of individuals at most locations.     

A stochastic reaction scheme for drug/metabolite interaction

We present a simplified stochastic model to investigate the mechanisms of action of tramadol, a centrally acting analgesic, used for treating pain. The model accounts for the process of metabolization through the cytochrome CYP2D6 and the interactions between molecules and target receptors. The proposed formulation is stochastic in nature and allows to speculate on the role of finite-size fluctuations. Analytically, the master equation, governing the process under scrutiny, is derived and studied in the mean-field limit. The analysis of the associated asymptotic behavior proves interesting for its potential medical implications. The analysis of fluctuations is carried on via the van Kampen expansion. Numerical simulations are also performed to confirm the adequacy of our theoretical prediction.     

Study of transcription of the human cytochrome P450IID6 gene by polymerase chain reaction]

Polymerase chain reaction was used to study the expression of the drug metabolism gene. Primers complementary to the 2070-2090 and 2912-2930 sites within exons 4 and 6 of the gene CYP2D6 were synthesized. The amplification of the cDNA from total human liver mRNA was achieved. The length of the fragment obtained (238 bp) was in accordance with the distance between the primers binding sites in cDNA. The amplification of the DNA from the same source led to the longer fragment due to the presence of introns. The total RNA from the blood cells of the extensive metabolizers was shown to contain the mRNA transcribed from the CYP2D6 gene. The Taq polymerase reaction in the presence of cDNA derived from a poor metabolizer did not lead to the synthesis of the 238 bp fragment.     

CYP2D6 Genotype Dependent Oxycodone Metabolism in Postoperative Patients

Background

The impact of polymorphic cytochrome P450 CYP2D6 enzyme on oxycodone''s metabolism and clinical efficacy is currently being discussed. However, there are only spare data from postoperative settings. The hypothesis of this study is that genotype dependent CYP2D6 activity influences plasma concentrations of oxycodone and its metabolites and impacts analgesic consumption.

Methods

Patients received oxycodone 0.05 mg/kg before emerging from anesthesia and patient-controlled analgesia (PCA) for the subsequent 48 postoperative hours. Blood samples were drawn at 30, 90 and 180 minutes after the initial oxycodone dose. Plasma concentrations of oxycodone and its metabolites oxymorphone, noroxycodone and noroxymorphone were analyzed by liquid chromatography-mass spectrometry with electrospray ionization. CYP2D6 genotyping was performed and 121 patients were allocated to the following genotype groups: PM (poor metabolizer: no functionally active CYP2D6 allele), HZ/IM (heterozygous subjects, intermediate metabolizers with decreased CYP2D6 activity), EM (extensive metabolizers, normal CYP2D6 activity) and UM (ultrarapid metabolizers, increased CYP2D6 activity). Primary endpoint was the genotype dependent metabolite ratio of plasma concentrations oxymorphone/oxycodone. Secondary endpoint was the genotype dependent analgesic consumption with calculation of equianalgesic doses compared to the standard non-CYP dependent opioid piritramide.

Results

Metabolism differed between CYP2D6 genotypes. Mean (95%-CI) oxymophone/oxycodone ratios were 0.10 (0.02/0.19), 0.13 (0.11/0.16), 0.18 (0.16/0.20) and 0.28 (0.07/0.49) in PM, HZ/IM, EM and UM, respectively (p = 0.005). Oxycodone consumption up to the 12^th hour was highest in PM (p = 0.005), resulting in lowest equianalgesic doses of piritramide versus oxycodone for PM (1.6 (1.4/1.8); EM and UM 2.2 (2.1/2.3); p<0.001). Pain scores did not differ between genotypes.

Conclusions

In this postoperative setting, the number of functionally active CYP2D6 alleles had an impact on oxycodone metabolism. The genotype also impacted analgesic consumption, thereby causing variation of equianalgesic doses piritramide : oxycodone. Different analgesic needs by genotypes were met by PCA technology in this postoperative cohort.     

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.     

Warfarin pharmacogenetics: CYP2C9 and VKORC1 genotypes predict different sensitivity and resistance frequencies in the Ashkenazi and Sephardi Jewish populations

Warfarin is a widely used anticoagulant that has a narrow therapeutic range because of both genetic and environmental factors. CYP2C9( *)2 (p.R144C), CYP2C9( *)3 (p.I359L), and the VKORC1 promoter (g.-1639G-->A) polymorphisms occur frequently in patients who are warfarin "sensitive" and require lower doses, whereas patients with VKORC1 missense mutations are warfarin "resistant" and require higher doses. To compare the CYP2C9 and VKORC1 allele and genotype frequencies among 260 Ashkenazi (AJ) and 80 Sephardi Jewish (SJ) individuals, we genotyped six CYP2C9 and eight VKORC1 alleles by using the Tag-It Mutation Detection Kit and PCR-RFLP assays. The "sensitive"CYP2C9( *)2 and ( *)3 alleles had significantly higher frequencies in SJ than in AJ individuals, 0.194 and 0.144 versus 0.127 and 0.081, respectively (p A, underscoring the importance of screening for p.D36Y prior to initiating warfarin anticoagulation in AJ individuals. Taken together, our findings show that approximately 85% of AJ and approximately 90% of SJ individuals have at least one "sensitive" (CYP2C9( *)2, ( *)3, VKORC1 g.-1639G-->A) or "resistant" (VKORC1 p.D36Y) allele, indicating that each group has different warfarin pharmacogenetics and would benefit from genotype-based dose predictions.     

Contribution of cytochrome P450 and ABCB1 genetic variability on methadone pharmacokinetics, dose requirements, and response

Although the efficacy of methadone maintenance treatment (MMT) in opioid dependence disorder has been well established, the influence of methadone pharmacokinetics in dose requirement and clinical outcome remains controversial. The aim of this study is to analyze methadone dosage in responder and nonresponder patients considering pharmacogenetic and pharmacokinetic factors that may contribute to dosage adequacy. Opioid dependence patients (meeting Diagnostic and Statistical Manual of Mental Disorders, [4(th) Edition] criteria) from a MMT community program were recruited. Patients were clinically assessed and blood samples were obtained to determine plasma concentrations of (R,S)-, (R) and (S)-methadone and to study allelic variants of genes encoding CYP3A5, CYP2D6, CYP2B6, CYP2C9, CYP2C19, and P-glycoprotein. Responders and nonresponders were defined by illicit opioid consumption detected in random urinalysis. The final sample consisted in 105 opioid dependent patients of Caucasian origin. Responder patients received higher doses of methadone and have been included into treatment for a longer period. No differences were found in terms of genotype frequencies between groups. Only CYP2D6 metabolizing phenotype differences were found in outcome status, methadone dose requirements, and plasma concentrations, being higher in the ultrarapid metabolizers. No other differences were found between phenotype and responder status, methadone dose requirements, neither in methadone plasma concentrations. Pharmacokinetic factors could explain some but not all differences in MMT outcome and methadone dose requirements.     

Enantioselectivity of debrisoquine 4-hydroxylation in Brazilian Caucasian hypertensive patients phenotyped as extensive metabolizers

Debrisoquine (D), an antihypertensive drug metabolized to 4-hydroxydebrisoquine (4-OHD) by CYP2D6, is commonly used as an in vivo probe of CYP2D6 activity and can be used to phenotype individuals as either extensive (EMs) or poor metabolizers (PMs) of such drugs as β-adrenergic blockers, tricyclic antidepressants, and class 1C antiarrhythmics. This report describes reversed-phase HPLC systems by which D and 4-OHD or S-(+) and R-(−)-4-OHD in urine are more selectively quantified without the need for derivatization techniques. We also studied the urinary excretion of R-(−)- and S-(+)-4-hydroxydebrisoquine in EM hypertensive patients in order to determine weather 4-OHD formation exhibits enantioselectivity. Twelve patients with mild to severe essential hypertension were admitted to the study. They received a single tablet of Declinax containing 10 mg debrisoquine sulfate. All the urine excreted during the following 8 h was collected. The debrisoquine metabolic ratio (DMR) was calculated as % of dose excreted as D/% of dose excreted as 4-OHD and the debrisoquine recovery ratio (DRR) was calculated as % of dose excreted as 4-OHD/% of dose excreted as D+4-OHD. Debrisoquine and its metabolite were determined in urine by HPLC using a reversed-phase Select B LiChrospher column, a mobile phase of 0.25 N acetate buffer, pH 5–acetonitrile (9:1, v/v) and a fluorescence detector. The limit of quantitation was determined to be 25.0 ng/ml for D and 18.75 ng/ml for 4-OHD. Intra- and inter-day relative standard deviations (RSDs) were less than 10%. All hypertensive patients studied showed a DMR of less than 12.6 or a DRR higher than 0.12 and were classified as EMs. Direct enantioselective separation on chiral stationary phase involved resolution of S-(+)-4-OHD and R-(−)-4-OHD on a Chiralcel OD-R column with a mobile phase of 0.125 N sodium perchlorate, pH 5–acetonitrile–methanol (85:12:3, v/v/v). The quantitation limit of each enantiomer was 3.75 ng/ml of urine. Intra- and inter-day RSDs were less than 10% for each enantiomer. A high degree of enantioselectivity in the 4-hydroxylation of D favouring the S-(+) enantiomer was observed, resulting in R-(−)-4-OHD not detected in the urine of the EM hypertensive patients studied.     

Debrisoquine/sparteine hydroxylation genotype and phenotype: analysis of common mutations and alleles of CYP2D6 in a European population.

Four different mutations of the cytochrome P450 CYP2D6 gene associated with the poor metabolizer phenotype (PM) of the debrisoquine/sparteine polymorphism were analyzed by Xba I restriction fragment length polymorphism (RFLP) analysis and a polymerase chain reaction (PCR)-based DNA amplification method in DNA of 394 healthy European subjects; 341 of these were phenotyped by sparteine or debrisoquine administration and urinary metabolic ratios (MR). Our study demonstrates the efficiency of the PCR-test for phenotype prediction; 96.4% of individuals were correctly predicted, i.e., 100% of the extensive metabolizers (EMs) and 86.0% of the poor metabolizers (PMs). In contrast, Xba I RFLP analysis was far less informative, predicting the phenotype in only 26.8% of PMs. By combining both DNA tests, the prediction rate of the PM phenotype increased to 90.6%. A point mutation at a splice-site consensus sequence termed D6-B represented the most common mutant CYP2D6 gene and accounted for more than 75% of mutant alleles. In addition, other known mutations such as D6-D (14%), D6-A (5%), and the rare D6-C mutation bring the identified mutant alleles to greater than 95% of all mutant PM-alleles. Most of Xba I 44-kb alleles were confirmed as mutant alleles carrying the D6-B mutation. However, 9.7% did not have this mutation and may express a functional CYP2D6 gene. Moreover, all Xba I 16 + 9-kb alleles contained the D6-B mutation. Heterozygous EM individuals had a significantly higher MR when compared to homozygous EMs. Genotyping provides an important advantage for investigations of the influence of CYP2D6 activity on drug therapy and its association with certain diseases.     

104名藏族志愿者中细胞色素P450 2C19m1的基因多态性

细胞色素P450 2C19（CYP2C19）参与临床上许多重要药物的代谢。根据其代谢S－美芬妥英或其他CYP2C19底物的能力不同,有强代谢者（EMs）和弱代谢者（PMs）之分。PMs表型的频发率存在明显的种族差异。在本文中,我们主要报道了细胞色素P450 2C19 m1在中国藏族人群中的多态性分布。在104例无血缘关系藏族人群中,49人（47.1%）为CYP2C19野生型纯合子（wt/wt）,46人（44.2%）为CYP2C19m1杂合子（wt/m1）,9人（8.7%）为CYP2C19m1突变型纯合子（m1/m1）。CYP2C19野生型等位基因频率为0.692,CYP2C19m1等位基因频率为0.308。该结果与国内外报道的中国其余民族的CYP2C19m1等位基因频率相比具有一定可比性。 关键词：细胞色素P450 2C19;基因型;藏族;聚合酶链反应;限制性内切核酸酶片段长度多态（RFLP）Abstract: Cytochrome P 450 2C19（CYP2C19） is involved in the metabolism of a number of clinically used drugs. Individuals can be characterized as extensive metabolizers （EMs）or poor metabolizers（PMs）, according to the drugs-metabolized ability of CYP2C19 in population studies. The incidence of poor metabolizer phenotype shows marked interracial differences. In this article we report the gene polymorphism of CYP2C19 in Zang population. There were 49 wild-type homozygotes（wt/wt）, 46 were heterozygotes（wt/m1） and 9 were homozygotes（m1/m1） among 104 unrelated Zang subjects. The frequency of CYP2C19m1 allele was 0.308, which was in agreement with that in other published data.     

Individualized therapy for gastroesophageal reflux disease: potential impact of pharmacogenetic testing based on CYP2C19

The main therapeutic agent for gastroesophageal reflux disease (GERD) is a proton pump inhibitor (PPI). Plasma levels and the acid inhibitory effect of PPIs depend on the activity of cytochrome P450 (CYP) 2C19, which is polymorphic. Genotypes of CYP2C19 are classified into three groups: rapid metabolizers (RMs: *1/*1), intermediate metabolizers (IMs: *1/*X), and poor metabolizers (PMs: *X/*X), where *1 and X represent the wild type and the mutant allele, respectively. RMs include ultra-rapid metabolizers, who possess the CYP2C19*17 allele. The pharmacokinetics and pharmacodynamics of PPIs differ among different CYP2C19 genotype groups. Plasma PPI levels and intragastric pH values during PPI treatment are lowest in the RM group, intermediate in the IM group, and highest in the PM group. These CYP2C19-genotype-dependent differences in the pharmacokinetics and pharmacodynamics of PPIs influence the healing and recurrence of GERD during PPI treatment, suggesting the need for CYP2C19 genotype-based tailored therapy for GERD. CYP2C19 pharmacogenetics should be taken into consideration for the personalization of PPI-based therapy. However, the clinical usefulness of CYP2C19 genotype testing in GERD therapy should be verified in clinical studies.