Effect of CYP3A5*3 genotype on the pharmacokinetics and antiplatelet effect of clopidogrel in healthy subjects

CYP3A4*22 Impairs the Elimination of Ticagrelor, But Has No Significant Effect on the Bioactivation of Clopidogrel or Prasugrel

CYP3A enzymes participate in the elimination of ticagrelor and the bioactivation of clopidogrel and prasugrel. We studied the effects of functional CYP3A genetic variants (CYP3A4*22; rs35599367 and CYP3A5*3; rs776746) on the pharmacokinetics and pharmacodynamics of ticagrelor, clopidogrel, and prasugrel. Six healthy volunteers with the CYP3A4*1/*22 and CYP3A5*3/*3 genotype (CYP3A4*22 carriers), eight with the CYP3A4*1/*1 and CYP3A5*1/*3 genotype (CYP3A5 expressors), and 11-13 with the CYP3A4*1/*1 and CYP3A5*3/*3 genotypes (controls) ingested single doses of ticagrelor, clopidogrel, and prasugrel on separate occasions. Ticagrelor area under the plasma concentration-time curve (AUC) was 89% (P = 0.004) higher in CYP3A4*22 carriers than in controls. CYP3A4*22 carriers also showed more pronounced platelet inhibition at 24 hours after ticagrelor ingestion than the controls (43% vs. 21%; P = 0.029). The CYP3A5 genotype did not affect ticagrelor pharmacokinetics. Neither CYP3A5 nor CYP3A4 genotypes significantly affected prasugrel or clopidogrel. In conclusion, the CYP3A4*22 allele markedly impairs ticagrelor elimination enhancing its antiplatelet effect.

Effects of CYP2D6 and CYP3A5 genetic polymorphisms on steady-state pharmacokinetics and hemodynamic effects of tamsulosin in humans

PURPOSE

Tamsulosin is one of the most potent drugs currently available to treat benign prostatic hyperplasia. Cytochrome P450 (CYP) 2D6 and CYP3A are the two major enzymes responsible for tamsulosin metabolism. The purpose of this study was to evaluate the effects of CYP2D6 and CYP3A5 genetic polymorphisms on the pharmacokinetics and hemodynamic effects of tamsulosin in humans.

METHODS

Twenty-nine male subjects were enrolled and their CYP2D6 (*2,*4,*5,*10,*14,*21,*41, and *xN) and CYP3A5 (*5) genotypes were screened. Tamsulosin was administered daily for 6 days to assess its steady-state pharmacokinetics and hemodynamic effects according to CYP2D6 and CYP3A5 genotypes.

RESULTS

CYP2D6 group 3 (with genotype *10/*10 or *5/*10) exhibited higher plasma levels than CYP2D6 group 1 (with genotype *1/*1,*1/*2,*1/*2xN, or *2/*10xN) or CYP2D6 group 2 (with genotype *1/*10,*1/*41, or *2/*5) (trough concentrations for groups 1, 2, and 3: 1.3, 1.8, and 3.8 ng/mL, respectively [P < 0.001]; peak concentrations for groups 1, 2, 3: 8.3, 10.0, and 13.8 ng/mL, respectively [P < 0.005]). Similarly, CYP2D6 genotypes influenced the hemodynamic effects of tamsulosin based on systolic and diastolic blood pressures. However, the CYP3A5*3 polymorphism did not affect tamsulosin plasma levels and its hemodynamic effects.

CONCLUSION

The CYP2D6 but not the CYP3A5 genetic polymorphisms affected the pharmacokinetics and the hemodynamic effects of tamsulosin.

CYP2C19 but not CYP2B6, CYP3A4, CYP3A5, ABCB1, PON1 or P2Y12 genetic polymorphism impacts antiplatelet response after clopidogrel in Koreans

Clopidogrel response variability (CRV) is well documented, and may affect clinical outcomes. Impact of genetic polymorphisms is important for assessing and predicting CRV. The extensive evidence indicates the importance of CYP2C19 variants in reducing efficacy of clopidogrel. This study defined the impact of numerous genetic polymorphisms on CRV before and after percutaneous coronary interventions (PCI) exclusively in a Korean cohort assuming less genetic variability noise. One hundred and thirty-six patients of Korean origin undergoing PCI were included. Platelet reactivity was measured by VerifyNow assay before and after PCI. Genetic polymorphism of seven single nucleotides of CYP2B6, CYP2C19, CYP3A4, CYP3A5, ABCB1, PON1, and P2Y12 were evaluated and matched with platelet reactivity. Carriers of at least one CYP2C19*2 or *3 allele uniformly exhibited higher platelet reactivity compared to 0-carrier pre-PCI (odds ratio 3.1, 95% confidence interval 1.4-6.9, P < 0.01) and post-PCI (odds ratio 3.4, 95% confidence interval 1.7-6.8, P < 0.001). The carriers of other gene allele variants lack uniformed impact on CRV. The Korean carriers of CYP2C19*2 or *3 allele are linked to CRV, whereas CYP2B6, CYP3A4, CYP3A5, ABCB1, PON1, and P2Y12 failed to predict CRV. The exact clinical utility of these findings is uncertain, and requires a large randomized national trial for proof of concept.

No Effect of SLCO1B1 and CYP3A4/5 Polymorphisms on the Pharmacokinetics and Pharmacodynamics of Ticagrelor in Healthy Chinese Male Subjects

Ticagrelor is a direct-acting P2Y12 receptor antagonist. It is rapidly absorbed and partly metabolized to the active metabolite AR-C124910XX by CYP3A4 and CYP3A5. Three genetic loci (SLCO1B1, CYP3A4, and UGT2B7) were reported to affect ticagrelor pharmacokinetics. This study aimed to investigate the possible effects of SLCO1B1 and CYP3A4/5 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of ticagrelor in healthy Chinese male volunteers. Eighteen healthy male volunteers who participated in pharmacogenetics study of ticagrelor were genotyped for SLCO1B1 rs113681054, SLCO1B1*5 (rs4149056), CYP3A4*1G (rs2242480), and CYP3A5*3 (rs776746). All subjects received a single 180 mg loading dose of ticagrelor and then series blood samples were collected from 0 to 48 h. Plasma concentrations of ticagrelor and AR-C124910XX were determined by the high performance liquid chromatography-tandem mass spectrometry method. Inhibition in platelet aggregation (IPA) was assessed and the area under the time-effect curve (AUEC) for the IPA was calculated as pharmacodynamic parameters. No significant difference in ticagrelor pharmacokinetics among genotypes of the two genes was observed. The AUEC did not differ significantly among genotypes of candidate single nucleotide polymorphisms (SNPs). Our data suggest that common genetic variants in SLCO1B1 and CYP3A4/5 may have no effect on the pharmacokinetics and pharmacodynamics of ticagrelor in healthy Chinese volunteers.

Association between CYP3A5 polymorphisms and the risk of adverse events in patients undergoing clopidogrel therapy: Meta-analysis

INTRODUCTION

We wished to explore the relationship between CYP3A5 polymorphisms and adverse events in patients undergoing clopidogrel therapy.

METHODS

A Boolean search of the PubMed, EMbase, OVID and Cochrane Library databases was conducted in April 2016. The primary outcome was major adverse cardiovascular events (MACE). The secondary outcome was bleeding events and resistance to the effects of clopidogrel. The CYP3A5 polymorphism was classified into three types: wild-type (AA), heterozygote (AG) and homozygous mutant (GG). We estimated pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) using the Mantel-Haenszel model.

RESULTS

Twelve studies involving 8284 patients were eligible for our meta-analysis. CYP3A5 polymorphisms had no obvious influence on MACE (AA+AG vs. GG: OR=1.032, 95% CI=0.583-1.824, p=0.915; AA vs. AG+GG: 1.415, 0.393-5.094, 0.595). There was no significant relationship between CYP3A5 polymorphisms and bleeding (GG vs. AA+AG: OR=0.798, 95% CI=0.370-1.721, p=0.565) or clopidogrel resistance (AA+AG vs. GG: 1.009, 0.685-1.488, 0.963; AA vs. AG+GG, 0.618, 0.368-1.039, 0.069).

CONCLUSION

No significant correlation was found between CYP3A5 polymorphisms and adverse events due to clopidogrel therapy.

The pharmacogenetic control of antiplatelet response: candidate genes and CYP2C19

INTRODUCTION

Aspirin, clopidogrel, prasugrel and ticagrelor are antiplatelet agents for the prevention of ischemic events in patients with acute coronary syndromes (ACS), percutaneous coronary intervention (PCI) and other indications. Variability in response is observed to different degrees with these agents, which can translate to increased risks for adverse cardiovascular events. As such, potential pharmacogenetic determinants of antiplatelet pharmacokinetics, pharmacodynamics and clinical outcomes have been actively studied.

AREAS COVERED

This article provides an overview of the available antiplatelet pharmacogenetics literature. Evidence supporting the significance of candidate genes and their potential influence on antiplatelet response and clinical outcomes are summarized and evaluated. Additional focus is directed at CYP2C19 and clopidogrel response, including the availability of clinical testing and genotype-directed antiplatelet therapy.

EXPERT OPINION

The reported aspirin response candidate genes have not been adequately replicated and few candidate genes have thus far been implicated in prasugrel or ticagrelor response. However, abundant data support the clinical validity of CYP2C19 and clopidogrel response variability among ACS/PCI patients. Although limited prospective trial data are available to support the utility of routine CYP2C19 testing, the increased risks for reduced clopidogrel efficacy among ACS/PCI patients that carry CYP2C19 loss-of-function alleles should be considered when genotype results are available.

Single nucleotide polymorphism of CYP3A5*3 contributes to clopidogrel resistance in coronary artery disease patients among Tamilian population

Clopidogrel is an antiplatelet drug. It is used for the treatment as well as for the prophylaxis of coronary artery disease. Clopidogrel resistance is an emerging problem in clinical settings. The aim of the present study was to evaluate the effect of CYP3A5*3 genetic polymorphism on clopidogrel resistance. One hundred and forty-seven patients from outpatient Department of Cardiology on 75 mg/day of clopidogrel as maintenance dose were recruited from April 2010 to July 2011. All subjects gave written informed consent to participate in the study. DNA extraction was performed using phenol chloroform extraction procedure and genotyping by standard Taqman based RT-PCR method. Platelet aggregation was done at the end of 7th and 14th day by using chronolog lumi Aggregometer which is expressed as impedance in ohms. Impedance values of >5 ohms at the end of 6 min were considered as clopidogrel resistance. Subjects (N = 147) were analysed for CYP3A5*3 polymorphism, of which 49 (33%) were found to be clopidogrel resistant. Homomutants of CYP3A5*3 gene had 2.78 (0.97-7.98; p < 0.05) fold risk and heteromutants had 2.4 (0.93-6.46; p < 0.05) fold risk of developing clopidogrel resistance. Carriers of defective allele G of CYP3A5*3 had higher propensity to cause clopidogrel resistance with an odds ratio of 1.63. Variant alleles and genotypes of CYP3A5*3 polymorphism contributed significantly to clopidogrel resistance with a higher odds ratio. Thus, pharmacogenomics paves way for the emergence of stratified medicine in clopidogrel therapy and personalised pharmacotherapy in ischaemic heart disease.

Effect of P2Y1 and P2Y12 genetic polymorphisms on the ADP-induced platelet aggregation in a Korean population

BACKGROUND

P2Y1 and P2Y12 receptors are expressed in platelet membranes and are involved in ADP-induced platelet aggregation. Genetic polymorphisms of P2Y1 and P2Y12 play a major role in the variation of ADP-induced platelet aggregation and in response in antiplatelet therapy.

OBJECTIVE

To evaluate the allele frequencies of P2Y1 and P2Y12 genetic polymorphisms in a Korean population and to assess their role in ADP (5 μmol/L)-induced maximal platelet aggregation.

METHODS

P2Y1 (c.1622A>G) and P2Y12 (i-139C>T, i-744T>C, i-ins801, c.52G>T, c.34C>T) polymorphisms were analyzed in 158 Korean healthy participants using pyrosequencing methods. Their ADP-induced maximal platelet aggregation was assessed by the turbidometric method.

RESULTS

The observed allele frequencies of P2Y1 and P2Y12 were as follows: 0.3101 for P2Y1 c.1622A>G; 0.1804 for P2Y12 i-139C>T, 0.1804 for i-744T>C, 0.1804 for i-801insA, 0.1266 for P2Y12 c.52G>T, and 0.2658 for P2Y12 c.34C>T. ADP-induced maximal platelet aggregation was not influenced by the P2Y1 c.1622A>G polymorphism and was also not affected by three intronic P2Y12 polymorphisms and the P2Y12 c.34C>T polymorphism. However, the P2Y12 c.52G>T polymorphism caused a substantial difference in ADP-induced maximal platelet aggregation (62.75% for c.52GG, 66.27% for c.52GT, and 80.60% for c.52TT; P=0.0092).

CONCLUSIONS

The P2Y1 and P2Y12 genes were very polymorphic in a Korean population. Three intronic P2Y12 polymorphisms (i-139C>T, i-744T>C, i-801insA) were in complete linkage disequilibrium but not with the c.52C>T polymorphism in this population. Maximal platelet aggregation in response to ADP is associated with the c.52C>T polymorphism but not with the three intronic polymorphisms or the P2Y1 c.1622A>T polymorphism.

The impact of CYP3A5*1/*3, PIA1/A2 and T744C polymorphisms on clopidogrel and acetylsalicylic acid response variability in Mexican population

INTRODUCTION

Clopidogrel is recommended in addition to aspirin to prevent atherothrombotic events in patients with acute coronary syndromes (ACS) and in those undergoing percutaneous coronary intervention (PCI). However, an interindividual variability in platelet inhibition response to clopidogrel has been demonstrated, and is associated with recurrent cardiovascular events. Multiple mechanisms have been associated with no response including genetics factors.

MATERIALS AND METHODS

The present study enrolled 60 patients with ACS undergoing emergent PCI. Platelet aggregation to adenosine diphosphate and arachidonic acid was assessed by turbidimetric method at 24 hours after dual administration of 300 mg of clopidogrel and 300 mg of acetylsalicylic acid loading dose. Clopidogrel or acetylsalicylic acid resistance was defined by persistence of Platelet Reactivity (PR=ADP-Ag >70% or PR=Arachidonic Acid-Ag>20%) respectively. The CYP3A51*/5*, PIA1/A2, and T744C polymorphisms were determined in all participants by PCR-RFLP.

RESULTS

The allelic frequencies were: CYP3A5*3 (71.65%), PIA2 (10.8%), and 744 C (15.0%). We founded high percent of clopidogrel resistance (60.0%), compared with 8.3% of acetylsalicylic acid in those patients. The genotype frequencies of those polymorphisms were similar between responders and non responders defined by PR. There was a high percent of coronary adverse events.

CONCLUSIONS

We identified a high percent of clopidogrel resistance in Mexican patients with ACS undergoing PCI. However, a normal platelet response to acetylsalicylic acid was observed in most of them. There was no association between CYP3A5*1/*3, PIA1/A2, and T744C polymorphisms and clopidogrel resistance. More studies are needed to determine the possible interaction between genetics factors, platelet response to clopidogrel and cardiovascular adverse events.

Prasugrel is effective and safe for neurointerventional procedures

BACKGROUND

Clopidogrel bisulfate and aspirin are routinely administered as dual antiplatelet agents for many neurointerventional procedures, especially for intravascular stent placement. Many patients are non-responsive to clopidogrel, either secondary to drug interactions or from variations of cytochrome P450 enzymes. Prasugrel (brand name Effient, Eli Lilly and Company, Indianapolis, IN, USA) is a new antiplatelet agent that has been utilized extensively in patients undergoing cardiovascular procedures but its safety and efficacy during neurointerventional procedures have not been evaluated.

OBJECTIVE

To examine whether prasugrel is a safe and effective alternative to clopidogrel for neurointerventional procedures, especially in those patients who are either non-responders or allergic to clopidogrel.

METHODS

The medical records of all patients undergoing neurointerventional procedures at our institution who received prasugrel between January 2009 and July 2011 were retrospectively reviewed. A systematic chart review was performed and the following data were recorded: demographics, aneurysm location, endovascular techniques, peri- and post-procedural complications, hemorrhagic complications, clinical outcome and angiographic outcome.

RESULTS

16 patients undergoing neurointerventional procedures received prasugrel over a 2 year interval. All patients who had follow-up studies of P2Y12 inhibition had immediate therapeutic response to prasugrel. There were no complications related to ischemic or intracranial hemorrhage.

CONCLUSION

Prasugrel is a viable alternative to clopidogrel for patients undergoing neurointerventional procedures who are non-responders to clopidogrel. Further study is needed to evaluate the safety, efficacy and cost-effectiveness of prasugrel compared with clopidogrel for patients undergoing neurointerventional procedures.

Ticagrelor versus genotype-driven antiplatelet therapy for secondary prevention after acute coronary syndrome: a cost-effectiveness analysis

BACKGROUND

Clopidogrel's effectiveness is likely reduced significantly for prevention of thrombotic events after acute coronary syndrome (ACS) in patients exhibiting a decreased ability to metabolize clopidogrel into its active form. A genetic mutation responsible for this reduced effectiveness is detectable by genotyping. Ticagrelor is not dependent on gene-based metabolic activation and demonstrated greater clinical efficacy than clopidogrel in a recent secondary prevention trial. In 2011, clopidogrel will lose its patent protection and likely will be substantially less expensive than ticagrelor.

OBJECTIVE

To determine the cost-effectiveness of ticagrelor compared with a genotype-driven selection of antiplatelet agents.

METHODS

A hybrid decision tree/Markov model was used to estimate the 5-year medical costs (in 2009 US$) and outcomes for a cohort of ACS patients enrolled in Medicare receiving either genotype-driven or ticagrelor-only treatment. Outcomes included life years and quality-adjusted life years (QALYs) gained. Data comparing the clinical performance of ticagrelor and clopidogrel were derived from the Platelet Inhibition and Patient Outcomes trial.

RESULTS

The incremental cost-effectiveness ratio (ICER) for universal ticagrelor was $10,059 per QALY compared to genotype-driven treatment, and was most sensitive to the price of ticagrelor and the hazard ratio for death for ticagrelor compared with clopidogrel. The ICER remained below $50,000 per QALY until a monthly ticagrelor price of $693 or a 0.93 hazard ratio for death for ticagrelor relative to clopidogrel. In probabilistic analyses, universal ticagrelor was below $50,000 per QALY in 97.7% of simulations.

CONCLUSION

Prescribing ticagrelor universally increases quality-adjusted life years for ACS patients at a cost below a typically accepted threshold.

Pharmacogenomics of clopidogrel: evidence and perspectives

Clopidogrel has become the mainstay oral antiplatelet regimen to prevent recurrent ischemic events after acute coronary syndromes or stent placement. However, there is marked interindividual variability in the antiplatelet effects of clopidogrel, and a reduced response to this drug may be a risk factor for ischemic complications. Pharmacogenomic analyses, including candidate-gene and genome-wide association studies, have confirmed that genetic polymorphisms in the hepatic cytochrome P450 (CYP) 2C19 dominantly affect the antiplatelet effects of clopidogrel. CYP2C19 reduced-function alleles have been associated with a significant decrease in clopidogrel responsiveness and a higher risk of adverse cardiac events including stent thrombosis, myocardial infarction, and death in several prospective studies, although these effects were not reproduced in a recent large randomized study that included a randomized control group. The US Food and Drug Administration addressed this issue by adding a boxed warning to the clopidogrel label and suggesting that adjusting the clopidogrel dose or using alternative antiplatelet agents should be potentially implemented for high-risk individuals who are identified based on the CYP2C19 genotype. Although it is promising that CYP2C19 genotyping could be used to guide personalized antiplatelet clopidogrel therapy, currently there is insufficient evidence to recommend routine genetic testing. Prospective randomized clinical trials are necessary to validate this pharmacogenomic approach to clopidogrel therapy. In the most recent trial, paraoxonase-1 (PON1) was identified as a crucial new enzyme for clopidogrel bioactivation, with its common Q192R polymorphism determining the rate of active metabolite and the clinical activity of clopidogrel. Further studies are needed to investigate the comprehensive influence of a number of different polymorphisms of CYP2C19 and PON1 variant alleles or other genetic variants on clopidogrel in various ethnic populations.

ABCG2 polymorphisms, 34G>A and 421C>A in a Korean population: analysis and a comprehensive comparison with other populations

BACKGROUND AND OBJECTIVE

ABCG2, also known as Breast Cancer Resistance Peptide (BCRP) or mitoxantrone-resistant protein, is the second member of the G-family of ABC transporters. The frequencies of ABCG2 34G>A and 421C>A polymorphisms in a Korean population were assessed using a newly developed multiplex pyrosequencing method, and compared with the corresponding frequencies seen in other ethnic groups.

METHOD

We designed a multiplex pyrosequencing method to simultaneously detect ABCG2 421C>A and 34G>A polymorphisms and analysed the allele frequencies of these polymorphisms in 250 Korean subjects.

RESULTS

The results showed 100% concordance between single and multiplex pyrosequencing methods. We also validated the polymorphisms identified by pyrosequencing with a direct sequencing method using randomly selected samples. The allele frequencies of ABCG2 421C>A and 34G>A in the population tested were 0·298 and 0·190 respectively. The allele frequency of the 421C>A polymorphism is comparable to other Asian populations, including Japanese and Chinese. However, both frequencies are different from those of Caucasians and Africans.

CONCLUSIONS

The multiplex pyrosequencing method used to detect two ABCG2 polymorphisms concurrently is a rapid and reliable genotyping method for the detection of important ABCG2 genetic polymorphisms. The ABCG2 34G>A and 421C>A polymorphisms are frequently found in the Korean population. The frequencies are similar to those seen in other Asian populations including Japanese and Chinese, but very different to those of Caucasian and African-American populations.

The missing linkage: what pharmacogenetic associations are left to find in CYP3A?

IMPORTANCE OF THE FIELD

An enormous amount of drugs and endogenous substrates are metabolized by the enzymes encoded in the CYP3A gene cluster, making variation at this locus of utmost importance in the field of pharmacogenetics. However, the identification of genetic variation that contributes to the wide phenotypic variability at this locus has been elusive. While dozens of studies have investigated the effects of coding variants, none have found the definitive answer to what variant or variants explain the distribution of enzyme activity and clinical effects seen with the drug metabolized by these genes.

AREAS COVERED IN THIS REVIEW

This review highlights the recent pharmacogenetic work at the CYP3A locus, in particular studies on known functional variants in CYP3A4 and CYP3A5. In addition, common pharmacogenetic strategies as well as considerations specific to the CYP3A locus are discussed.

WHAT THE READER WILL GAIN

The reader will gain a greater understanding of the complexities involved in studying the CYP3A locus, population differences that may affect pharmacogenetic studies at this locus and the importance of variation that affect gene regulation.

TAKE HOME MESSAGE

More innovative and comprehensive methods to assay this region are needed, with particular attention paid to the role of gene regulation and non-coding sequence.

Effect of CYP3A5*3 genotype on serum carbamazepine concentrations at steady-state in Korean epileptic patients

BACKGROUND AND OBJECTIVE

Carbamazepine (CBZ) is metabolized mainly by the CYP3A family of enzymes, which includes CYP3A4 and CYP3A5. Several studies have suggested that the CYP3A5*3 genotype influences the pharmacokinetics of CYP3A substrates. The present study aimed to assess the effect of the CYP3A5*3 genotype on serum concentration of CBZ at the steady-state in Korean epileptic patients.

METHOD

The serum concentrations of CBZ in 35 Korean epileptic patients were measured and their CYP3A5 genotype was determined. Fourteen patients were CYP3A5 expressors (two for CYP3A5*1/*1 and 12 for CYP3A5*1/*3) and 21 patients were CYP3A5 non-expressors (CYP3A5*3/*3). Dose-normalized concentrations (mean +/- SD) of CBZ were 9.9 +/- 3.4 ng/mL/mg for CYP3A5 expressors and 13.1 +/- 4.5 ng/mL/mg for CYP3A5 non-expressors (P = 0.032). The oral clearance of CBZ was significantly higher in CYP3A5 non-expressors than that of CYP3A5 expressors (0.056 +/-0.017 L/h/kg vs. 0.040 +/- 0.014 L/h/kg, P = 0.004). The CYP3A5 genotype affected the CBZ concentrations in Korean epileptic patients and is a factor that may contribute to inter-individual variability in CBZ disposition in epileptic patients.

Bioequivalence and tolerability of two clopidogrel salt preparations, besylate and bisulfate: a randomized, open-label, crossover study in healthy Korean male subjects

BACKGROUND

Clopidogrel, a potent antiplatelet agent, reduces the risk for thrombotic events in patients with atherothrombotic diseases. Clopidogrel is marketed primarily as a bisulfate salt. A different salt preparation of clopidogrel, clopidogrel besylate, has been developed and might provide an additional treatment option for patients.

OBJECTIVE

The aim of this study was to compare the pharmacokinetic, pharmacodynamic, and tolerability profiles of clopidogrel besylate with those of clopidogrel bisulfate to determine bioequivalence for the purposes of marketing approval.

METHODS

A randomized, open-label, 2-period, single- and multiple-dose, comparative crossover study was conducted in healthy Korean male subjects. The subjects received either clopidogrel bisulfate or clopidogrel besylate as a single 300-mg oral loading dose (day 1) followed by a 75-mg/d (once daily) maintenance dose on days 2 to 6. After a 15-day washout period, subjects were administered the alternative salt preparation according to the same protocol. The plasma concentrations of clopidogrel and its primary metabolite (SR26334) were assessed using high-performance liquid chromatography/tandem mass spectrometry after administration of the loading dose. The platelet aggregation response to 10-mumol/L adenosine diphosphate was measured using turbidometric aggregometry during the single- and multiple-dosing periods and at steady state (day 6). Tolerability was monitored using physical examination, including vital sign measurements, and laboratory analysis.

RESULTS

Forty-four subjects were enrolled and completed the study (mean [SD] age, 24.3 [2.7] years; weight, 70.0 [8.2] kg). The mean values for C(max), T(max), and AUC(0-t) with clopidogrel (parent drug) of clopidogrel besylate (5.2 ng/mL, 0.9 hour, and 10.1 ng/mL/h, respectively) were similar to those with clopidogrel bisulfate (5.4 ng/mL, 0.9 hour, and 10.3 ng/mL/h). The mean values for Cmax, AUC(0-t), and AUC(0-infinity) with the SR26334 of clopidogrel besylate (10.9 microg/mL, 38.8 microg/mL/h, and 43.0 microg/mL/h, respectively) were not significantly different from those with the SR26334 of clopidogrel bisulfate (11.9 microg/mL, 40.6 microg/mL/h, and 43.8 microg/mL/h). The mean values for maximal antiplatelet effect (Emax) and area under the time-effect curve (AUEC) with the 2 clopidogrel salt preparations were as follows: clopidogrel besylate, 58.8 h . % and 4299.1 h . % inhibition, respectively; and clopidogrel bisulfate, 61.7 h . % and 4406.9 h . % inhibition; these differences were not statistically significant. The 90% CIs for the ratios of the log-transformed C(max), AUC, E(max), and AUEC values were within the predetermined bioequivalence range of 80% to 125%. Three adverse events (6.8%) were reported during the study and included abdominal discomfort (1 subject [2.3%] in the group that received clopidogrel bisulfate), easy fatigability (1 subject [2.3%] immediately before administration of loading dose of clopidogrel besylate), and thrombocytopenia (1 subject [2.3%] in the group receiving the clopidogrel bisulfate). All adverse events were transient and mild.

CONCLUSIONS

In these healthy Korean male subjects, the differences in the pharmacokinetic and pharmacodynamic properties between the 2 clopidogrel salt preparations did not reach statistical significance and met the regulatory requirements for bioequivalence. Both preparations were well tolerated.

Effects of CYP2D6 and CYP3A5 genotypes on the plasma concentrations of risperidone and 9-hydroxyrisperidone in Korean schizophrenic patients

This study was conducted to evaluate the effects of the CYP2D6 and CYP3A5 genotypes on the steady-state plasma levels of risperidone (RIS), 9-hydroxyrisperidone (9-OH-RIS), and the active moiety (RIS plus 9-OH-RIS) in Korean schizophrenic patients. Sixty-four Korean schizophrenic patients were enrolled. CYP2D6 and CYP3A5 genotypes were determined, and the plasma levels of RIS and 9-OH-RIS were measured using high-performance liquid chromatography. The dose-normalized plasma concentrations of RIS, 9-OH-RIS, and the active moiety were compared according to the CYP2D6 and CYP3A5 genotypes. Among the patients, 57 were CYP2D6 extensive metabolizers (EMs; CYP2D6*1/*1, *1/*10, and *10/*10) and 7 were CYP2D6 poor metabolizers (PMs; CYP2D6*1/*5 and *10/*5). For the CYP3A5 genotype, 30 patients were CYP3A5*1 expressors (*1/*1 [n = 1] and *1/*3 [n = 29]) and 34 patients were CYP3A5 nonexpressors (*3/*3). The plasma levels of RIS (2.03 ng/mL per milligram for EMs vs 5.57 ng/mL per milligram for PMs, P < 0.001) and 9-OH-RIS (5.06 ng/mL per milligram for EMs vs 0.22 ng/mL per milligram for PMs, P < 0.001) were significantly different among CYP2D6 genotype groups, but the CYP2D6 EMs (7.09 ng/mL per milligram) and PMs (5.79 ng/mL per milligram) did not show no difference in the levels of the active moiety (P = 0.470). CYP3A5 nonexpressors exhibited higher plasma concentrations of both RIS and 9-OH-RIS than its expressors. In the case of 9-OH-RIS, CYP3A5 nonexpressors exhibited significantly higher concentrations than CYP3A5 expressors (5.42 vs 3.51 ng/mL per milligram, P = 0.022). In addition, concentrations of the active moiety were also significantly different between the CYP3A5 nonexpressors (8.39 ng/mL per milligram) and expressors (5.30 ng/mL per milligram, P = 0.005). In conclusion, both CYP2D6 and CYP3A5 genotypes affected plasma levels of RIS and 9-OH-RIS, whereas the active moiety levels were influenced only by the CYP3A5 genotype but not by the CYP2D6 genotype.

Clopidogrel resistance: pharmacokinetic or pharmacogenetic?

Clopidogrel is important for the management of acute coronary syndromes and, along with aspirin, is recommended in the American College of Cardiology/American Heart Association guideline. It is also used along with aspirin, during the placement of coronary artery stents. Clopidogrel resistance was recognized in such procedures, as several patients did not have the anticipated platelet aggregation response to an ex vivo adenosine diphosphate challenge. From the EXCELSIOR study, which investigated the phenomenon, it was appreciated that it was present prior to treatment with clopidogrel and was therefore an intrinsic property of the patient's platelets. From other studies, it was appreciated that the patients who had clopidogrel resistance had a defective allele *2/ in the CYP2C19 gene. Furthermore, there was a dose response evident in that the homozygotes CYP2C19*2/*2 had platelets that responded even less well to clopidogrel than the heterozygotes CYP2C19*2 that responded less well than the wild-type homozygote. The involvement of the phenomenon with CYP2C19 led some to believe that it was a pharmacokinetic issue. However, the major oxidative metabolic pathway for clopidogrel by which the reactive intermediate is formed is CYP3A4. It is suggested that there is a linkage between a polymorphism of the platelet receptor P2Y12 and the polymorphism of CYP2C19.