CYP2D6 polymorphism in relation to tramadol metabolism: a study of faroese patients

Several studies have demonstrated the impact of CYP2D6 polymorphism on the pharmacokinetics of tramadol. However, the relationship between the O-demethylation of tramadol and O-desmethyltramadol (M1) and CYP2D6 activity has not previously been investigated with tramadol in multimedicated outpatients under steady-state conditions. Hence, the aim of this study was to determine if the well documented pharmacokinetics of tramadol regarding CYP2D6 could be verified in a study including 88 multimedicated Faroese patients, treated with tramadol at steady-state conditions. Further, the study aimed to investigate whether the previously observed frequency of CYP2D6 poor metabolizers (PMs) in the Faroese, which was shown to be double that of other Europeans, was evident in a patient group medicated with a CYP2D6 substrate. The patients were CYP2D6-phenotyped by the intake of sparteine, followed by urine collection over 12 hours. Sparteine and its metabolites were assayed by gas chromatography. Genotype analyses for the CYP2D6 3, 4, 6, and 9 alleles were performed by polymerase chain reaction and Taqman technology. Plasma and urinary concentrations of (+/-)-tramadol and (+/-)-M1 were determined by high-performance liquid chromatography. With use of CYP2D6 phenotyping, 10 patients (11.5% [95% confidence interval (CI), 5.7-20.1%]) were classified as CYP2D6 PMs, and 8 (9.3% [95% CI, 4.1-17.3%]) of these were genotyped as CYP2D6 PMs. The PM frequency was not statistically significantly higher than that in other European populations (7%-10%). The concentrations of (+)-M1 when corrected for dose (nM/mg) and the (+)-M1/(+)-tramadol ratio were approximately 14-fold higher in the extensive metabolizers (EMs) than in the PMs. In conclusion, the impact of the CYP2D6 polymorphism on the pharmacokinetics of tramadol was clearly demonstrated in a group of multimedicated patients treated with tramadol under steady-state conditions. Further, the frequency of PMs was not higher than that in other European populations, as previously shown in different Faroese groups, possibly because of discontinued tramadol treatment in Faroese patients who were PMs.     

CYP2D6表面型决定16名中国汉族受试者普罗帕酮对映体药物动力学 …

目的：研究ＣＹＰ２Ｄ６表达型在汉族健康受试者普罗帕桐对映体代谢中的作用。和右美沙芬进行代谢分型后得到的７名极快代谢得（ＶＥＭ）和９名中速代谢者（ＩＭ）。单剂量口服消旋普罗帕酮４００ｍｇ,抽取０－１５ｈ静脉血,运用反相高压液相色谱法加柱前衍生化,定量分析血浆中普罗帕酮对映体深度。结果：两种ＣＹＰ２Ｄ６表现型的Ｓ－Ｐｒｏ代谢均较Ｒ－Ｐｒｏ慢,血浆浓度升高。此外ＩＭ中Ｒ－Ｐｒｏ对映体在ＶＥＭ和ＩＭ中的代     

CYP2D6表现型决定16名中国汉族受试者普罗帕酮对映体药物动力学的差异

目的:研究CYP2D6表现型在汉族健康受试者普罗帕酮对映体代谢中的作用。方法:选取用右美沙芬进行代谢分型后得到的7名极快代谢者(VEM)和9名中速代谢者(IM)。单剂量口服消旋普罗帕酮400mg,抽取0-15h静脉血。运用反相高压液相色谱法加柱前衍生化,定量分析血浆中普罗帕酮对映体浓度。结果:两种CYP2D6表现型的S-Pro代谢均较R-Pro慢,血浆浓度升高。此外,IM中R-Pro的半衰期比R-Pro大,VEM无此差别。但是,Pro对映体在VEM和IM中的代谢有明显差异。IM组两种对映体的C_(max)和AUC均比VEM组大(P<0.05)。IM组Pro对映体的Cl仅为VEM组的一半[(67±17)vs(133±28)L·h~(-1)for S-Pro,(90±24)vs(200±87)L·h~(-1)for R-Pro,P<0.0]。T_(1/2),T_(max),C_(max),Cl和AUC的S/R比值无显著差异(P>0.05)。结论:CYP2D6表现型决定了普罗帕酮对映体的药动学差异,EM受试者中IM的存在也许与中国人CYP2D6酶活性下降有关。     

细胞色素P—450 CYP2D6基因分型与表型的吻合率

研究细胞色素Ｐ４５０－２Ｄ６基因分型测定方法及其与表型的吻合率。方法：利用等位基因特异扩增法基本原理,对ＣＹＰ２Ｄ６酶缺陷等位基因ＣＹＰ２Ｄ６＊３,＊４,＊６和＊７进行测定。结果;通过１６８例基因分型,并将结果与表型对照,发现同时测定ＣＹＰ２Ｄ６＊３,＊４,＊６和＊７等位基因时,１２５例快代谢者和４３例慢代谢者的基因分型结果与表型结果的吻合率为１００％。     

Near-fatal tramadol cardiotoxicity in a CYP2D6 ultrarapid metabolizer

Background  

Tramadol is a synthetic, centrally acting analgesic for the treatment of moderate to severe pain. The marketed tramadol is a racemic mixture containing 50% (+)tramadol and 50% (−)tramadol and is mainly metabolized to O-desmethyltramadol (M1) by the cytochrome P450 CYP2D6. Tramadol is generally considered to be devoid of any serious adverse effects of traditional opioid receptor agonists, such as respiratory depression and drug dependence.     

细胞色素P-450 CYP2D6基因分型与表型的吻合率

目的:研究细胞色素P-450 2D6基因分型测定方法及其与表型的吻合率。方法:利用等位基因特异扩增法基本原理,对CYP2D6酶缺陷等位基因CYP2D6*3,*4,*6和*7进行测定。结果:通过168例基因分型,并将结果与表型对照,发现同时测定CYP2D6*3,*4,*6和*7等位基因时,125例快代谢者和43例慢代谢者的基因分型结果与表型结果的吻合率为100％。快代谢者至少有一个野生型CYP2D6等位基因,基因型为*1/*1,*1/*3和*1/*4。发现慢代谢者是CYP2D6突变型纯合子,基因型为*3/*4,*4/*4,*3/*6,*4/*7,*4/*6和*6/*6。结论:对CYP2D6*3,*4,*6和*7等位基因的测定能够准确预测其表型。     

Enantioselective pharmacokinetics of tramadol in CYP2D6 extensive and poor metabolizers

Objective To describe in detail the intravenous, single oral and multiple oral dose enantioselective pharmacokinetics of tramadol in CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs).Methods Eight EMs and eight PMs conducted three phases as an open-label cross-over trial with different formulations; 150 mg single oral tramadol hydrochloride, 50 mg single oral tramadol hydrochloride every 8 h for 48 h (steady state), 100 mg intravenous tramadol hydrochloride. Urine and plasma concentrations of (+/−)-tramadol and (+/−)-M1 were determined for 48 h after administration.Results In all three phases, there were significant differences between EMs and PMs in AUC and t_1/2 of (+)-tramadol (P≤0.0015), (−)-tramadol (P≤0.0062), (+)-M1 (P≤0.0198) and (−)-M1 (P≤0.0370), and significant differences in C_max of (+)-M1 (P<0.0001) and (−)-M1 (P≤0.0010). In Phase A and C, significant differences in t_max were seen for (+)-M1 (P≤0.0200). There were no statistical differences between the absolute bioavailability of tramadol in EMs and PMs. The urinary recoveries of (+)-tramadol, (−)-tramadol, (+)-M1 and (−)-M1 were statistically significantly different in EMs and PMs (P<0.05). Median antimodes of the urinary metabolic ratios of (+)-tramadol / (+)-M1 and (−)-M1 were 5.0 and 1.5, respectively, hereby clearly separating EMs and PMs in all three phases.Conclusion The impact of CYP2D6 phenotype on tramadol pharmacokinetics was similar after single oral, multiple oral and intravenous administration displaying significant pharmacokinetic differences between EMs and PMs of (+)-tramadol, (−)-tramadol, -(+)-M1 and (−)-M1. The O-demethylation of tramadol was catalysed stereospecific by CYP2D6 in the way that very little (+)-M1 was produced in PMs.     

Pharmacokinetics of hydralazine and its acid-labile hydrazone metabolites in relation to acetylator phenotype

The pharmacokinetics of hydralazine (H) and its acid-labile hydrazone metabolites were compared in rapid and slow acetylators. Following a 20-mg intravenous infusion, the elimination half-life (t_1/2) and the apparent volume of distribution of H did not differ between the two groups. Plasma clearance estimates approached hepatic blood flow. When a single 100-mg dose of H was given-orally, the area under the plasma concentration-time curve (AUC) and systemic availability () in slow acetylators were, on the average, twice as high as in the rapid acetylators, indicating a difference in the extent of first-pass metabolism of the drug. Furthermore, the observed in the slow individuals exceeded theoretical predictions. Hence saturation of first-pass metabolism of H is suggested, and a nonlinear relationship between AUC and oral dose of H was indeed observed in the three subjects studied with two doses. The half-life of decline of the acidlabile metabolites was similar to the t_1/2 of H. The AUCs for metabolites were 4–12 times larger than for the parentdrug. However, the ratio between the metabolite AUC and drug AUC did not differ irrespective ofroutes of administration or the acetylator status.This study was supported in part by Grant RR 828 from United States Public Health Service and a Research Starter grant from the Pharmaceutical Manufacturers Association Foundation, Inc. (D. D. S.).     

Polymorphic CYP2D6 mediates O-demethylation of the opioid analgesic tramadol

Objective: This study was designed to investigate whether the in vivo metabolism of tramadol was influenced by CYP2D6 polymorphism. Methods: The extent of tramadol O- and N-demethylation was calculated by determining the amounts of tramadol and O- and N-desmethyltramadol in 24 h urine after ingestion of a test dose of tramadol. The O- and N-demethylation rates were calculated by dividing the 24-h urinary excretion amount of tramadol by that of O-and N-desmethyltramadol. Volunteers were phenotyped for CYP2D6 polymorphism using sparteine as an in vivo probe. Results and conclusion: High correlation was found between tramadol-O-demethylation and sparteine oxidation in 71 extensive metabolizers of sparteine (r _s= 0.544). The mean metabolic ratio of tramadol O-demethylation was significantly higher in poor metabolizers of sparteine than in extensive metabolizers (4.4 vs 0.8). These in vivo results confirm that tramadol O-demethylation is carried out to a large extent by the polymorphic CYP2D6. Received: 9 January 1997 / Accepted in revised form: 23 July 1997     

CYP2D6 polymorphism in a Gabonese population: contribution of the CYP2D6*2 and CYP2D6*17 alleles to the high prevalence of the intermediate metabolic phenotype

AIMS: To determine the molecular basis of the intermediate extensive metaboliser (EM) CYP2D6 phenotype in healthy Gabonese subjects. METHODS: The CYP2D6 phenotype of 154 healthy Gabonese subjects was assessed by giving the subject a single dose of 30 mg dextromethorphan, and collecting their urine for the next 8 h. The CYP2D6 genotype was determined for 50 individuals of the EM phenotypic group by Southern blotting and various PCR-based procedures aimed at identifying different CYP2D6 alleles. RESULTS: We found that in the studied Gabonese population, as compared with a French population, there is significantly higher frequency of intermediate EM phenotype having lower frequency of CYP2D6 PM alleles. To clarify this discrepancy phenotype-genotype relationship was studied. We found that the CYP2D6*17 and CYP2D6*2 alleles, prevalent in this black population, are characterised by their low capacity for dextromethorphan demethylation. Our data also show that the CYP2D6*1 allele is associated with the highest in vivo activity followed by the CYP2D6*2 allele and then the CYP2D6*17 allele. CONCLUSIONS: The higher frequencies of the CYP2D6*2 and CYP2D6*17 alleles than the CYP2D6*1 allele account for the high frequency of the intermediate EM phenotype in this black population. The polymorphism of the CYP2D6 enzyme activity in African populations could have important implications for use of drugs that are substrates for CYP2D6 and have a narrow therapeutic window.     

Correlation of tramadol pharmacokinetics and CYP2D6*10 genotype in Malaysian subjects

The aim of the present study is to investigate the influence of the CYP2D6*10 allele on the disposition of tramadol hydrochloride in Malaysian subjects. A single dose of 100 mg tramadol was given intravenously to 30 healthy orthopaedic patients undergoing various elective surgeries. After having obtained written informed consents, patients were genotyped for CYP2D6*10: the most common CYP2D6 allele among Asians by means of allele-specific polymerase chain reaction. The presence of other mutations (CYP2D6*1, *3, *4, *5, *9 and *17) was also investigated. Tramadol was extracted from 1 ml serum with an n-hexane: ethylacetate combination (4:1) after alkalinisation with ammonia (pH 10.6). Serum concentrations were measured by means of high-performance liquid chromatography. The pharmacokinetics of tramadol was studied during the 24 h after the dose. As among other Asians, the allele frequency for CYP2D6*10 among Malaysians was high (0.43). Subjects who were homozygous for CYP2D6*10 had significantly (P=0.046) longer mean serum half-life of tramadol than subjects of the normal or the heterozygous group (Kruskal-Wallis test). When patients were screened for the presence of other alleles, the pharmacokinetic parameter values were better explained. CYP2D6 activity may play a main role in determining tramadol pharmacokinetics. The CYP2D6*10 allele particularly was associated with higher serum levels of tramadol compared with the CYP2D6*1 allele. However, genotyping for CYP2D6*10 alone is not sufficient to explain tramadol disposition.     

The antitussive effect of dextromethorphan in relation to CYP2D6 activity

AIMS: To test the hypothesis that inhibition of cytochrome P450 2D6 (CYP2D6) by quinidine increases the antitussive effect of dextromethorphan (DEX) in an induced cough model. METHODS: Twenty-two healthy extensive metaboliser phenotypes for CYP2D6 were studied according to a double-blind, randomised cross-over design after administration of: (1) Placebo antitussive preceded at 1 h by placebo inhibitor; (2) 30 mg oral DEX preceded at 1 h by placebo inhibitor (DEX30); (3) 60 mg oral DEX preceded at 1 h by placebo inhibitor (DEX60); (4) 30 mg oral DEX preceded at 1 h by 50 mg oral quinidine sulphate (QDEX30). Cough frequency following inhalation of 10% citric acid was measured at baseline and at intervals up to 12 h. Plasma concentrations of DEX and its metabolites were measured up to 96 h by h.p.l.c. RESULTS: Inhibition of CYP2D6 by quinidine caused a significant increase in the mean ratio of DEX to dextrorphan (DEX:DOR) plasma AUC(96) (0.04 vs 1.81, P<0.001). The mean (+/-s.d.) decrements in cough frequency below baseline over 12 h (AUEC) were: 8% (11), 17% (14.5), 25% (16.2) and 25% (16.9) for placebo, DEX30, DEX60 and QDEX30 treatments, respectively. Statistically significant differences in antitussive effect were detected for the contrasts between DEX60/placebo (P<0.001; 95% CI of difference +80, +327) and QDEX30/placebo (P<0.001, +88, +336), but not for DEX30/placebo, DEX30/DEX60 or DEX30/QDEX30 (P=0.071, -7, +241; P=0.254, -37, +211; P=0.187, -29, +219, respectively). CONCLUSIONS: A significant antitussive effect was demonstrated after 60 mg dextromethorphan and 30 mg dextromethorphan preceded by 50 mg quinidine using an induced cough model. However, although the study was powered to detect a 10% difference in cough response, the observed differences for other contrasts were less than 10%, such that it was possible only to imply a dose effect (30 vs 60 mg) in the antitussive activity of DEX and enhancement of this effect by CYP2D6 inhibition.     

Relationship between fluvoxamine pharmacokinetics and CYP2D6/CYP2C19 phenotype polymorphisms

Objective: The purpose of this study was to investigate whether the disposition of fluvoxamine is associated with the CYP2D6 and CYP2C19 phenotype polymorphisms. Methods: The serum concentration of fluvoxamine was followed for 48 h after oral administration of a single dose of 50 mg fluvoxamine to five poor metabolizers of the CYP2D6 test drug dextromethorphan, five poor metabolizers of the CYP2C19 test drug mephenytoin, and five extensive metabolizers of both test drugs. Results: Poor metabolizers of dextromethorphan had significantly higher areas under the serum concentration-time curve than extensive metabolizers of dextromethorphan (mean 1.31 vs 1.00 μmol · h · l⁻¹). There were no differences between poor and extensive metabolizers of mephenytoin (mean, 1.00 vs 1.15 μmol · h · l⁻¹). Conclusion: The results are consistent with a possible minor to moderate role of CYP2D6, but not CYP2C19, in fluvoxamine metabolism. Received: 25 April 1996 / Accepted in revised form: 12 November 1996     

Metabolism of citalopram enantiomers in CYP2C19/CYP2D6 phenotyped panels of healthy Swedes

AIMS: To investigate pharmacokinetics of the enantiomers of citalopram (CT) and its metabolites desmethylcitalopram (DCT) and didesmethylcitalopram (DDCT) in Swedish healthy volunteers in relation to CYP2C19 and CYP2D6 geno- and phenotypes. METHODS: Racemic CT was given for seven days to panels with different genotypes and the following mephenytoin (Me) and debrisoquine (De) hydroxylation phenotypes: EMDe/EMMe, PMDe/EMMe, EMDe/PMMe (n = 6 in all groups), and one PMDe/PMMe subject. Blood sampling was carried out during day 7, and all urine was collected for 12 h after the last dose of CT. RESULTS: The AUC of S-CT was significantly higher in the EMDe/PMMe panel compared to the EMDe/EMMe and PMDe/EMMe panels (P < 0.05), whereas the AUC of R-CT did not differ between the panels. Similar differences, although they did not reach statistical significance, were noted for S-DCT and R-DCT. The enantiomers of DDCT were not quantifiable in PMDe, and there was no difference in DDCT enantiomer concentrations between the other two panels. A PMDe/PMMe subject stopped taking CT after five days due to severe adverse effects. Based on two time points, this subject had a very long CT half-life of 95 h. The value of 1.0 for the S/R ratio of the CT trough in this subject was similar to the mean S/R CT trough ratio of the EMDe/PMMe panel, but higher than the S/R CT ratio of the EMDe/EMMe panel (0.56; 95% CI 0.49-0.63) and the PMDe/EMMe panel (0.44; 95% CI 0.31-0.57). Thus the latter two phenotypes eliminated S-CT more rapidly via CYP2C19. An adverse effect described as an 'alcohol hangover' feeling was reported by one subject from each of the three panels. These individuals had the highest concentrations of both CT enantiomers. CONCLUSIONS: The AUC of S-, but not R-(CT) was found to be significantly higher in PM of mephenytoin compared to EMs, PMs may need a lower dosage of CT.     

Evaluation of CYP2D6 phenotype in the Yoruba Nigerian population

Background: There is a lack of information on CYP2D6, a major metabolizing enzyme, in Africa ethnic nationalities. The objective was to determine CYP2D6 phenotype in Yoruba Nigerians using dextromethorphan (DEX).

Method: A total of 89 healthy volunteers received 30 mg of DEX orally followed by blood and urine sample collection at 3-hour and over 8 h post-dose, respectively. DEX and dextrorphan (DOR) concentrations were determined using High Performance Liquid Chromatography (HPLC). The metabolic ratio (MR, DEX/DOR) were plotted for the phenotype determination.

Results: The log MR that separated poor (PMs) from normal metabolizers (NMs) was 0.28 and 0.75 for urine and plasma, respectively. Two subjects (2.3%) identified as PMs had a mean MR of 17 and 3.2 in plasma and urine, significantly higher than that of NMs (p < .0001). A positive correlation between urine and plasma MR was noted.

Conclusion: The prevalence of PMs in the Yoruba Nigerians was similar to that reported among blacks.