Active Metabolite Exposure Research Articles

Whole Body PBPK Modeling of Remdesivir and Its Metabolites to Aid in Estimating Active Metabolite Exposure in the Lung and Liver in Patients With Organ Dysfunction.

Remdesivir (RDV) is the first drug approved by the US Food and Drug Administration (FDA) for the treatment of coronavirus disease 2019 (COVID-19) in certain patients requiring hospitalization. As a nucleoside analogue prodrug, RDV undergoes intracellular multistep activation to form its pharmacologically active species, GS-443902, which is not detectable in the plasma. A question arises that whether the observed plasma exposure of RDV and its metabolites would correlate with or be informative about the exposure of GS-443902 in tissues. A whole body physiologically-based pharmacokinetic (PBPK) modeling and simulation approach was utilized to elucidate the disposition mechanism of RDV and its metabolites in the lungs and liver and explore the relationship between plasma and tissue pharmacokinetics (PK) of RDV and its metabolites in healthy subjects. In addition, the potential alteration of plasma and tissue PK of RDV and its metabolites in patients with organ dysfunction was explored. Our simulation results indicated that intracellular exposure of GS-443902 was decreased in the liver and increased in the lungs in subjects with hepatic impairment relative to the subjects with normal liver function. In subjects with severe renal impairment, the exposure of GS-443902 in the liver was slightly increased, whereas the lung exposure of GS-443902 was not impacted. These predictions along with the organ impairment study results may be used to support decision making regarding the RDV dosage adjustment in these patient subgroups. The modeling exercise illustrated the potential of whole body PBPK modeling to aid in decision making for nucleotide analogue prodrugs, particularly when the active metabolite exposure in the target tissues is not available.

Pharmacogenomic\u2013pharmacokinetic study of selective estrogen-receptor modulators with intra-patient dose escalation in breast cancer

BackgroundAn association between CYP2D6 polymorphisms and tamoxifen (TAM) efficacy has not been confirmed, partly due to unreliable prediction of active metabolite exposure solely by CYP2D6 activity. The efficacy of TAM dose escalation appears limited in poor TAM metabolizers. Since the chlorine atom on the side chain of toremifene (TOR) prevents 4-hydroxylation by CYP2D6, its contribution to active conversion of TOR is minor. We examined the role of TOR and its dose escalation among poor TAM metabolizers.MethodsThe pharmacokinetics (PK) and pharmacogenomics (PGx) of TAM and TOR were studied. Correlation between PK and CYP2D6 inhibitor use, smoking status, and PGx were examined by regression analysis. For patients showing low endoxifen levels, an intra-patient dose escalation of TOR was conducted, and TOR was increased from 40 to 120 mg for ≥ 24 weeks with PK sampling. Total activity was calculated as the sum of the concentration of each active metabolite adjusted by their respective in vitro activities.ResultsFifty and 11 of the 273 participating patients had endoxifen levels < 15 and < 7.5 ng/mL, respectively. The CYP2D6 genotype was the major determinant for TAM activity (p < 0.01). Smoking status (p = 0.07) and the CYP2C19 phenotype (p = 0.07), but not the CYP2D6 genotype (p = 0.61), showed marginally significant effects on TOR activity. TOR activity increased significantly with dose escalation, even among poor TAM metabolizers, and was maintained for ≥ 24 weeks.ConclusionTOR might be a valid alternative to TAM in patients predicted to be poor TAM metabolizers.

Gene variants in responsiveness to clopidogrel have no impact on clinical outcomes in Chinese patients undergoing percutaneous coronary intervention — A multicenter study

BackgroundGene variants contribute to variability in individual responsiveness to clopidogrel and influence cardiovascular outcomes in Caucasian patients with acute coronary syndrome (ACS). However, limited data is available in Asian populations. MethodsWe resequenced 14 genes in metabolizing and activity pathway of clopidogrel in 138 patients with ACS and prospectively assessed the modulating effects of 13 variants possibly related to clopidogrel efficacy on one-year cardiovascular event occurrence in 5820 ACS patients after percutaneous coronary intervention (PCI). In addition, platelet aggregation rate was measured in 1084 participants and plasma levels of active metabolite were determined in 15 patients to test whether increasing clopidogrel maintenance doses increases active metabolite exposure. ResultsNo significant associations were found between any of the tested variants and risk of cardiovascular events (P>0.05), although CYP2C19*2 carriers had slightly higher on-treatment platelet aggregation rate and lower active metabolite exposure compared with that of non-carriers (Median [IQR] 51.49 [35.43–66.75] vs. 49.05 [32.36–63.38], P=0.012) (means±SD AUC, 22.84±5.00 vs. 35.05±12.34, P=0.008). Switching from 75mg daily clopidogrel to 150mg daily fully overcomes low exposure to clopidogrel active metabolite in CYP2C19*2 carriers (means±SD AUC, 32.35±8.65 vs. 35.05±12.34, P=0.314). ConclusionDifferent from Caucasian populations, genetic variants have no significant influence on clinical outcomes and have much milder effects on inhibition of platelet and active clopidogrel metabolite levels in Chinese patients with ACS after PCI, an effect which could be overcome with a dose escalation to 150mg daily.

Species Comparison of Pre-systemic Bioactivation of Vicagrel, a New Acetate Derivative of Clopidogrel.

Previously we have found vicagrel, a new acetate derivative of clopidogrel, underwent hydrolysis to 2-oxo-clopidogrel and subsequent conversions to its pharmacological active metabolite (AM) and inactive carboxylic acid metabolite (CAM). This study demonstrated the interspecies differences of the vicagrel bioactivation by comparing the critical vicagrel metabolites formation in rats, dogs and human. The pharmacokinetic studies with rats and dogs were conducted after intragastric administration of vicagrel, followed by in vitro metabolism investigation in venous system, intestinal/hepatic microsomes from rats, dogs and human. An obvious disparity was observed in system exposure to AM (99.0 vs. 635.1 μg⋅h/L, p < 0.05) and CAM (10119 vs. 2634 μg⋅h/L, p < 0.05) in rats and dogs. It was shown that the cleavage of vicagrel was almost completed in intestine with great different clearance (53.28 vs. 3.643 L⋅h-1⋅kg-1, p < 0.05) in rats and dogs. With no further hydrolysis to CAM, the greatest clearance of AM (3.26 mL⋅h-1⋅kg-1) was found in dog intestine. In rat plasma, 2-oxo-clopidogrel was much more extensively hydrolyzed to CAM than in dog and human. Albeit similar hydrolysis clearance and AM production was observed among hepatic microsomes of the three species, the production velocity of CAM ranked highest in dogs (7.55 pmol/min/mg protein). Therefore, the unconformity of AM and CAM exposure cross species mainly came from the metabolism of 2-oxo-clopidogrel associated largely with tissue specificity and interspecies differences of esterases. In human, the pharmacokinetics of vicagrel might be more optimistic due to less inactivation hydrolysis before reaching liver.

Abstract CT153: Pharmacokinetic drug interactions between abemaciclib and CYP3A inducers and inhibitors

Abstract Abemaciclib is a selective and potent small-molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) being investigated for treatment of refractory hormone-receptor positive (HR+) advanced or metastatic breast cancer. In vitro, CYP3A is responsible for &amp;gt;99% of the CYP-mediated microsomal metabolism of abemaciclib and its active metabolites. Three clinical studies evaluated the disposition and metabolism and drug interaction potential of abemaciclib in the presence of a strong CYP3A-inducer, rifampin, or a strong CYP3A-inhibitor, clarithromycin. Abemaciclib disposition and metabolism were determined following a single oral 150 mg dose of [14C]-abemaciclib in healthy subjects (N = 6). In the rifampin interaction study, abemaciclib was administered as a single oral 200 mg dose in healthy subjects (N = 24) on 2 occasions: alone on Day 1 of Period 1 and in combination with 600 mg rifampin on Day 7 of Period 2, after 6 days of rifampin once daily (QD) dosing; rifampin continued QD for 7 days after abemaciclib. In the clarithromycin interaction study, abemaciclib was administered as a single oral 50 mg dose in patients with advanced cancer (N = 26) on 2 occasions: alone in Period 1 and on Day 5 of clarithromycin dosing (500 mg BID) in Period 2 followed by an additional 7 days of clarithromycin. Abemaciclib was extensively metabolized, with less than 10% of parent drug recovered unchanged in feces. Parent drug and 3 active metabolites; (LSN2839567 [M2], LSN3106729 [M18], and LSN3106726 [M20]) were detected in plasma. The mean t1/2 in healthy subjects was 29.0, 104.0, 55.9, and 43.1 hours for abemaciclib, M2, M18, and M20, respectively. Coadministration with rifampin compared to abemaciclib alone decreased abemaciclib AUC(0-?) and Cmax by 95% and 92%, respectively, and decreased AUC(0-?) and Cmax of total active species (abemaciclib + M2 + M18+ M20) by 77% and 45%, respectively. Coadministration with clarithromycin compared to abemaciclib alone increased abemaciclib AUC(0-?) and Cmax by 237% and 30%, respectively; and increased the total active species AUC(0-?) by 119% and decreased Cmax by 7%. The mean abemaciclib t1/2 was prolonged from 28.8 to 63.6 hours. No clinically significant safety concerns were observed following single doses of abemaciclib in healthy subjects or in patients with advanced cancer based on vital signs, clinical laboratory evaluations, and electrocardiogram data. The human absorption, distribution, metabolism and excretion study indicated that abemaciclib was cleared primarily by hepatic metabolism, and the clinical drug-drug interaction studies with strong CYP3A inducer and inhibitor substantiated the major role of CYP3A in the metabolism of abemaciclib. Due to significant changes in abemaciclib and active-metabolite exposure in the presence of strong CYP3A inducers and inhibitors, concomitant use with abemaciclib should be avoided, or abemaciclib dose may require adjustment. Citation Format: Palaniappan Kulanthaivel, Daruka Mahadevan, P. Kellie Turner, Jane Royalty, Wee Teck Ng, Ping Yi, Jessica Rehmel, Kenneth Cassidy, Jill Chappell. Pharmacokinetic drug interactions between abemaciclib and CYP3A inducers and inhibitors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT153.

Effectiveness of clopidogrel dose escalation to normalize active metabolite exposure and antiplatelet effects in CYP2C19 poor metabolizers

Carriers of two copies of the loss-of-function CYP2C19*2 variant convert less clopidogrel into its active metabolite, resulting in diminished antiplatelet responses and higher cardiovascular event rates. To evaluate whether increasing the daily clopidogrel dose in poor metabolizers (PM) overcomes the effect of the CYP2C19 * 2 variant, we enrolled 18 healthy participants in a genotype-stratified, multi-dose, three-period, fixed-sequence crossover study. Six participants with the *1/*1 extensive (EM), *1/*2 intermediate (IM), and *2/*2 poor metabolizer genotypes each received 75 mg, 150 mg, and 300 mg each for 8 days. In each period, maximal platelet aggregation 4 hours post-dose (MPA4) and active metabolite area under the curve (AUC) differed among genotype groups (P < .05 for all). At day 8, PMs needed 300 mg daily and IMs needed 150 mg daily to attain a similar MPA4 as EMs on the 75 mg dose (32.6%, 33.2%, 31.3%, respectively). Similarly, PMs needed 300 mg daily to achieve active metabolite concentrations that were similar to EMs on 75 mg (AUC 37.7 and 33.5 ng h/mL, respectively). These results suggest that quadrupling the usual clopidogrel dose might be necessary to overcome the effect of poor CYP2C19 metabolism.

Clopidogrel metaboliser status based on point-of-care CYP2C19 genetic testing in patients with coronary artery disease

We compared results obtained with the Nanosphere Verigene® System, a novel point-of-care (POC) genetic test capable of analysing 11 CYP2C19 variants within 3 hours, to an established, validated genotyping method (Affymetrix™ DMET+; reference assay) for identifying extensive and reduced metabolisers of clopidogrel. Based on genotyping, patients (N=82) with stable coronary artery disease on clopidogrel 75 mg daily were defined as extensive metabolisers (*1/*1, *1/*17, *17/*17), reduced metabolisers (*1/*2, *1/*8, *2/*2, *2/*3), or of indeterminate metaboliser status (*2/*17). Pharmacokinetic exposure to clopidogrel's active metabolite and pharmacodynamic measures with P2Y12 reaction units (PRU) (VerifyNow®P2Y12 assay) and VASP PRI (PRI) were also assessed. There was a 99.9% overall concordance of marker-level data between the Nanosphere Verigene and DMET+ systems in identifying the CYP2C19 variants and 100% agreement in classifying the patients as extensive (n=59) or reduced metabolisers (n=15). Extensive metabolisers had significantly higher active metabolite exposure than reduced metabolisers (LS means 12.6 ng*h/ml vs 7.7 ng*h/ml; p<0.001). Extensive metabolisers also had lower PRU (LS means 158 vs 212; p=0.003) and VASP PRI (LS means 48% vs 63%, p=0.01) compared to reduced metabolisers. Rates of high on-treatment platelet reactivity were higher in reduced metabolisers compared to extensive metabolisers (VASP PRI ≥ 50%: 79% vs 47%; PRU >235: 33% vs 16%). The Nanosphere Verigene CBS system identified 11 CYP2C19 alleles in less than 3 hours with a high degree of accuracy when compared to a conventional method, and was further validated against pharmacokinetic and pharmacodynamic phenotypes.

The Influence of Smoking Status on the Pharmacokinetics and Pharmacodynamics of Clopidogrel and Prasugrel: The PARADOX Study

The goal of this study was to evaluate the effect of smoking on the pharmacokinetics and pharmacodynamics (PD) of clopidogrel and prasugrel therapy. Major randomized trial data demonstrated that nonsmokers experience less or no benefit from clopidogrel treatment compared with smokers (i.e., the “smokers' paradox”). PARADOX was a prospective, randomized, double-blind, double-dummy, placebo-controlled, crossover study of objectively assessed nonsmokers (n = 56) and smokers (n = 54) with stable coronary artery disease receiving aspirin therapy. Patients were randomized to receive clopidogrel (75 mg daily) or prasugrel (10 mg daily) for 10 days and crossed over after a 14-day washout. PD was assessed by using VerifyNow P2Y12 and vasodilator-stimulated phosphoprotein phosphorylation assays. Clopidogrel and prasugrel metabolite levels, cytochrome P450 1A2 activity, CYP2C19 genotype, and safety parameters were determined. During clopidogrel therapy, device-reported inhibition of platelet aggregation (IPA) trended lower in nonsmokers than smokers (least squares mean treatment difference ± SE: 7.7 ± 4.1%; p = 0.062). Device-reported IPA was significantly lower in clopidogrel-treated smokers than prasugrel-treated smokers (least squares mean treatment difference: 31.8 ± 3.4%; p < 0.0001). During clopidogrel therapy, calculated IPA was lower and P2Y12 reaction units and vasodilator-stimulated phosphoprotein phosphorylation and platelet reactivity index were higher in nonsmokers than in smokers (p = 0.043, p = 0.005, and p = 0.042, respectively). Greater antiplatelet effects were present after prasugrel treatment regardless of smoking status (p < 0.001 for all comparisons). PARADOX demonstrated lower clopidogrel active metabolite exposure and PD effects of clopidogrel in nonsmokers relative to smokers. Prasugrel was associated with greater active metabolite exposure and PD effects than clopidogrel regardless of smoking status. The poorer antiplatelet response in clopidogrel-treated nonsmokers may provide an explanation for the smokers' paradox. (The Influence of Smoking Status on Prasugrel and Clopidogrel Treated Subjects Taking Aspirin and Having Stable Coronary Artery Disease; NCT01260584)

Pharmacodynamic Comparisons for Single Loading Doses of Prasugrel (30mg) and Clopidogrel (600mg) in Healthy Korean Volunteers

Previous studies involving a loading dose (LD) of 60 mg prasugrel have suggested that active metabolite exposure and pharmacodynamic responses may be higher in persons of Asian ethnicity than in Caucasian subjects. The aim of this study was to determine the pharmacodynamic effect of an LD of 30 mg prasugrel and 600 mg clopidogrel in healthy Korean volunteers. Twelve volunteers were randomly assigned to a prasugrel or a clopidogrel group. Following a 2-week washout period, group designations and treatments were switched (6 per group). Platelet function was serially measured via light transmission aggregometry (LTA), VerifyNow and multiple electrode platelet aggregometry (MEA) assays at baseline and 0.5, 2, 6, and 24h after LD. Inhibition of platelet aggregation (IPA) at 0.5-24 h after prasugrel was significantly higher (P<0.001) than that achieved by clopidogrel. The prasugrel peak IPA at 2 h after LD was 93.7% (±6.2%) compared to the clopidogrel peak IPA at 6h after LD at 65.8% (±17.2%). The VerifyNow and MEA assay yielded results similar to those obtained by LTA. In healthy Korean subjects, a 30-mg LD of prasugrel yields a more rapid, potent and consistent inhibition of platelet function than a 600-mg LD of clopidogrel.

Measured Drug Effect and Cardiovascular Outcomes in Patients Receiving Platelet P2Y12Receptor Antagonists

THE CLINICAL EFFICACY OF ORAL P2Y12 ANTAGOnists in reducing recurrent cardiovascular events in patients with acute coronary syndromes (ACS) treated with percutaneous coronary intervention (PCI) or with either a conservative or early invasive strategy is well established. However, the effect of clopidogrel on P2Y12-mediated platelet reactivity varies widely among individuals. Platelet function tests are now clinically available that can measure P2Y12-mediated platelet reactivity, thereby providing a measurement of drug effect in patients treated with a P2Y12-receptor antagonist. Platelet function testing has provided a measure of certainty to the understanding of cardiovascular diseases: agents that provide powerful and consistent inhibition of P2Y12-mediated reactivity reduce postprocedural myocardial infarction and stent thrombosis, confirming the mechanistic hypothesis that P2Y12-receptor signaling is a major component of pathophysiological thrombus formation in patients with ACS treated with PCI. In turn, however, platelet function testing has added uncertainty because if platelet reactivity among patients while receiving treatment (“on-treatment” reactivity) is a measure of the risk of future events, then the comparative benefit of the newer, more expensive P2Y12 antagonists may uniquely depend on the magnitude of the effect of clopidogrel in a particular individual (however, different drugs may differentially affect the P2Y12 site. This concept of selective intensive antiplatelet therapy based on a measured drug effect, which has not been proven in a definitive, randomized trial, has provoked intense debate in the cardiology community. Although substantial data indirectly support the validity of the platelet function testing hypothesis, randomized trials to date have been limited by insufficient power, insufficient pharmacodynamic intervention, and potential selection bias for low-risk patients. Platelet function testing was not systematically performed in the trial that demonstrated the superiority of prasugrel over clopidogrel in patients with ACS treated with PCI. It is therefore speculative whether the benefit of prasugrel could be greatest in patients who demonstrate the least drug effect while receiving clopidogrel or could be minimal in patients treated with clopidogrel who display a potent drug effect. In this issue of JAMA, Gurbel and colleagues report the results of the platelet function substudy of the Targeted Platelet Inhibition to Clarify the Optimal Strategy to Medically Manage Acute Coronary Syndromes (TRILOGY ACS) trial, which included 2564 patients, approximately 28% of those enrolled in the overall trial. In the overall trial, prasugrel was not superior to clopidogrel in reducing recurrent cardiovascular events in medically managed patients with ACS who were not intended to undergo revascularization. In the current study, the investigators measured on-treatment reactivity at several time points over the course of follow-up using the VerifyNow P2Y12 test, which has been previously shown to reliably measure the P2Y12 effect of clopidogrel and prasugrel as well as correlate with active metabolite exposure of both drugs. The goals of the platelet function substudy were 2-fold: to confirm that prasugrel at the doses used provided a greater drug effect (ie, lower on-treatment reactivity) than clopidogrel and to determine whether there was an association between the achieved level of reactivity over time and clinical outcomes, irrespective of study drug assignment. At all time points tested, patients randomly assigned to receive 10 mg of prasugrel (or 5-mg prasugrel if aged 75 years or weight 60 kg) displayed significantly lower levels of on-treatment reactivity than those

Reduction in Platelet Reactivity With Prasugrel 5 mg in Low-Body-Weight Patients Is Noninferior to Prasugrel 10 mg in Higher-Body-Weight Patients: Results From the FEATHER Trial

The aim of this study was to confirm prior modeling data suggesting that prasugrel 5 mg in low-body-weight (LBW) patients would be noninferior to prasugrel 10 mg in higher-body-weight (HBW) patients as assessed by maximal platelet aggregation (MPA). Prasugrel 10 mg reduced ischemic events compared with clopidogrel 75 mg but increased bleeding, particularly in LBW patients. In this blinded, 3-period, crossover study in stable patients with coronary artery disease (CAD) taking aspirin, prasugrel 5 and 10 mg and clopidogrel 75 mg were administered to LBW (56.4 ± 3.7 kg; n = 34) and HBW patients (84.7 ± 14.9 kg; n = 38). Assays included light transmission aggregometry (LTA), VerifyNow P2Y12 (VN), and vasodilator-associated stimulated phosphoprotein (VASP) level measured predose and after each 12-day treatment. Median MPA by LTA for prasugrel 5 mg in LBW patients was noninferior to the 75th percentile for prasugrel 10 mg in HBW patients (primary endpoint) and mean MPA was similar, but active metabolite exposure was lowered by 38%. Within LBW patients, prasugrel 5 mg lowered MPA more than clopidogrel (least squares mean difference [95% confidence interval]: -3.7% [-6.72%, -0.69%]) and resulted in lower rates of high on-treatment platelet reactivity (HPR). Within HBW patients, prasugrel 10 mg lowered MPA more than clopidogrel (-16.9% [-22.3%, -11.5%]). Similar results were observed by VN and VASP. Prasugrel 10 mg in LBW patients was associated with more mild to moderate bleeding (mainly bruising) compared with prasugrel 5 mg and clopidogrel. In aspirin-treated patients with CAD, prasugrel 5 mg in LBW patients reduced platelet reactivity to a similar extent as prasugrel 10 mg in HBW patients and resulted in greater platelet inhibition, lower HPR, and similar bleeding rates compared with clopidogrel. (Comparison of Prasugrel and Clopidogrel in Low Body Weight Versus Higher Body Weight With Coronary Artery Disease [FEATHER]; NCT01107925).

TCT-726 Residual Platelet Reactivity Threshold After Clopidogrel Loading Dose to Predict Long-term Clinical Outcome in Patients with Acute Coronary Syndrome: Insights from the RECLOSE2-ACS Study

validated laboratory-based genotyping method. Methods: 74 stable CAD patients on clop 75 mg daily were tested by clinical nurses with no genetic laboratory experience and 1 hour of basic training on the device. The patients were defined as EM (*1/*1, *1/*17, *17/*17), RM (*1/*2A, *1/*8, *2A/*2A, *2A/*3). Genetic testing was conducted on 1 mL of whole blood using the Verigene® System and compared to an Affymetrix® DMET assay. Pharmacokinetic (PK) exposure to clop’s active metabolite (AM) was measured and platelet reactivity (PD) was assessed with the VerifyNowTM P2Y12 system (PRU) and VASP (PRI) assays. Results: There was an overall 99.9% concordance of marker-level data between the Verigene® and the reference (DMET ) in measuring the CYP2C19 markers of interest. There was a 100% agreement between Verigene® and the reference test in classifying the patients into established EM and RM groups. The POC assay identified 59 EM, 15 RM. The EM group had significantly lower PRU (LS means 158 vs. 212; p 0.003), and PRI (LS means 48 vs. 63, p 0.01) than RM group treated with clopidogrel 75 mg. The EM group also had significantly higher AM exposure by AUC(0-last) than the RM group (LS means 12.6 vs. 7.7; p 0.0009). Conclusions: This is the first report of a POC genetic testing platform performing a comprehensive CYP2C19 polymorphism characterization in CAD patients and validating the genotypes against the PK and PD phenotype. There was a high concordance between the two platforms in measuring the star allele marker data. The POC genetic test identified EM and RM phenotypes based on 11 gene variants with high accuracy and predicted a reduced platelet inhibition in response to clop. A rapid, reliable POC CYP2C19 genetic test could make clop pharmacogenetic testing feasible for all patients.

Platelet Function Testing and Genotyping Improve Outcome in Patients Treated With Antithrombotic Agents

The only reason P2Y12 inhibitors are administered in addition to aspirin is to improve the prevention of thrombosis. The clinical efficacy of adding clopidogrel to aspirin as a secondary prevention strategy in patients with high-risk coronary artery disease is well established.1 There are no effects of clopidogrel on any receptor other than P2Y12 to explain the magnitude of the clinical benefit. All of the established clinical effects are attributed to reduced platelet responsiveness to ADP.2 Therefore, the patient with inadequate P2Y12 inhibition determined by ex vivo testing logically has an increased risk for thrombosis. Persistent ischemic event occurrence and the irrefutable demonstration of clopidogrel antiplatelet response variability are 2 potent arguments against the widely practiced nonselective or one-size-fits-all strategy of administering clopidogrel therapy. Observational studies conducted in thousands of patients have led to an international consensus that high on-treatment platelet reactivity (HPR) to ADP is a major risk factor for post–percutaneous coronary intervention (PCI) ischemic event occurrence.3,4 Moreover, the recent 2011 American and European guidelines have given a Class IIb recommendation for platelet function testing or genotyping if the results of testing may alter management.5–7 Furthermore, the Society of Thoracic Surgeons gave a Class IIb recommendation for platelet function testing to determine the timing of surgery in patients on clopidogrel therapy (Level of Evidence C).8 These recommendations for personalizing antiplatelet therapy are unprecedented and acknowledge that a large body of data has accrued demonstrating the relation of HPR to ischemic risk in the PCI-treated patient. Finally, the evidence of diminished effectiveness of clopidogrel in poor metabolizers (those having 2 loss-of-function [LoF] cytochrome P450 [ CYP ] 2C19 alleles) has been recognized by the Food and Drug Administration (FDA) boxed warning about treatment with clopidogrel.9 Response by Krishna …

Pharmacokinetics and pharmacodynamics following maintenance doses of prasugrel and clopidogrel in Chinese carriers of CYP2C19 variants

This open-label, two-period, randomized, crossover study was designed to determine the effect of CYP2C19 reduced function variants on exposure to active metabolites of, and platelet response to, prasugrel and clopidogrel. Ninety healthy Chinese subjects, stratified by CYP2C19 phenotype, were randomly assigned to treatment with prasugrel 10 mg or clopidogrel 75 mg for 10 days followed by 14 day washout and 10 day treatment with the other drug. Eighty-three subjects completed both treatment periods. Blood samples were collected at specified time points for measurement of each drug's active metabolite (Pras-AM and Clop-AM) concentrations and determination of inhibition of platelet aggregation (IPA) by light transmittance aggregometry. CYP2C19 genotypes were classified into three predicted phenotype groups: rapid metabolizers [RMs (*1/*1)], heterozygous or intermediate metabolizers [IMs (*1/*2, *1/*3)] and poor metabolizers [PMs (*2/*2, *2/*3)]. Pras-AM exposure was similar in IMs and RMs (90% CI 0.85, 1.03) and slightly lower in PMs than IMs (90% CI 0.74, 0.99), whereas Clop-AM exposure was significantly lower in IMs compared with RMs (90% CI 0.62, 0.83), and in PMs compared with IMs (90% CI 0.53, 0.82). IPA was more consistent among RMs, IMs and PMs in prasugrel treated subjects (80.2%, 84.2% and 80.2%, respectively) than in clopidogrel treated subjects (59.7%, 56.2% and 36.8%, respectively; P < 0.001). Prasugrel demonstrated higher active metabolite exposure and more consistent pharmacodynamic response across all three predicted phenotype groups compared with clopidogrel, confirming observations from previous research that CYP2C19 phenotype plays an important role in variability of response to clopidogrel, but has no impact on response to prasugrel.

Genetic Polymorphisms and the Impact of a Higher Clopidogrel Dose Regimen on Active Metabolite Exposure and Antiplatelet Response in Healthy Subjects

A double-blind crossover study was conducted in four CYP2C19 genotype-defined metabolizer groups to assess whether increase in clopidogrel dosing can overcome reduced pharmacodynamic response in CYP2C19 poor metabolizers (PMs). Ten healthy subjects in each of four metabolizer groups were randomized to a clopidogrel regimen of a 300-mg loading dose (LD) and a 75-mg/day maintenance dose (MD) for 4 days followed by 600-mg LD and 150 mg/day MD, or vice versa. The exposure levels of clopidogrel's active metabolite H4 (clopi-H4) in PMs were 71% lower on the 75-mg/day regimen and 64% lower on the 150-mg/day regimen than the corresponding exposure levels in extensive metabolizers (EMs). In PMs, the maximal platelet aggregation (MPA) induced by adenosine diphosphate (ADP) 5 µmol/l was 10.5% lower on the 75-mg/day regimen and 7.9% lower on the 150-mg/day regimen than the corresponding values in EMs. PMs who were on the clopidogrel regimen of 600-mg LD/150 mg/day MD showed clopi-H4 exposure and MPA levels similar to those in EMs who were on the regimen of 300-mg LD/75 mg/day MD. In a pooled analysis evaluating CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP3A5, CYP2D6, ABCB1, and P2RY12 polymorphisms (N = 396 healthy subjects), only CYP2C19 had a significant impact on antiplatelet response. In healthy CYP2C19 PMs, a clopidogrel regimen of 600-mg LD/150 mg/day MD largely overcomes diminished clopi-H4 exposure and antiplatelet response, as assessed by MPA levels.

ACCF/AHA Clopidogrel Clinical Alert: Approaches to the FDA “Boxed Warning”

The recent US Food and Drug Administration (FDA) “boxed warning” on clopidogrel raises important questions for practitioners and patients. The warning addresses the need for pharmacogenomic testing to identify patients’ altered clopidogrel metabolism and thus their risk for a suboptimal clinical response to clopidogrel. Although there is an expanding database on genetic polymorphisms that may affect clopidogrel metabolism and thus clinical outcomes, there are no evidence-based data upon which todevelop specific recommendations on the role of genetic testing in routine care nor strategies proven to improve the safety/efficacy of specific pharmacologic approaches. To provide guidance on this issue, the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) convened a writing committee. The ACCF and AHA adhere to a rigorous policy regarding relationships with industry and other entities (RWI) of authors and peer reviewers for clinical document development (see http://www.cardiosource.org/Science-And-Quality/Practice-Guidelines-and-Quality-Standards/Relationships-With-Industry-Policy.aspx). This policy requires that a majority of writing committee members have no relevant relationships with industry to this topic, a standard that has been achieved for this document as indicated in Appendix 1. In the spirit of full disclosure, comprehensive RWI (RWI not relevant to this document) for all authors is available online for public view. RWI …

Pharmacodynamics and pharmacokinetics of single doses of prasugrel 30 mg and clopidogrel 300 mg in healthy chinese and white volunteers: An open-label trial

Background: Prasugrel is an oral antiplatelet agent approved for the reduction of atherothrombotic cardiovascular events in patients presenting with acute coronary syndrome and undergoing percutaneous coronary intervention. Although the approved loading dose is 60 mg, earlier studies of prasugrel suggested that active-metabolite exposure and pharmacodynamic response may be higher in Asian subjects than in white subjects. Objectives: This study compared the pharmacodynamic response to a single 30-mg dose of prasugrel in healthy Chinese and white subjects and the response to a single 30-mg dose of prasugrel and a single 300-mg dose of clopidogrel in healthy Chinese subjects. The pharmacokinetics and tolerability of both drugs were also assessed. Methods: This was an open-label, single-dose study conducted in Singapore. Chinese subjects were randomly allocated to receive prasugrel 30 mg or clopidogrel 300 mg; after a 14-day washout period, they received the alternative drug. White subjects received only prasugrel 30 mg. Blood samples for pharmaco-dynamic assessments were collected before dosing and at 0.5, 1, 2, 4, and 24 hours after dosing. Three methods were used to measure inhibition of platelet aggregation (IPA)—traditional light transmission aggregometry (LTA), the Verify Now P2Y12 (VN-P2Y12) assay, and a vasodilator-stimulated phosphoprotein (VASP) phosphorylation flow cytometry assay—and their results were compared. Blood samples for pharmacokinetic assessments were collected at 0.25, 0.5, 1, 1.5, 2, 4, 8, 12, and 24 hours after dosing. Concentrations of the active metabolite of prasugrel were measured using a validated LC-MS/MS method. Results: The study enrolled 18 Chinese subjects and 14 white subjects. Chinese subjects had a mean (SD) age of 31 (10) years and a mean body weight of 65.2 (8.9) kg; 83% were male. The corresponding values for white subjects were 30 (10) years, 77.2 (12.4) kg, and 86%. Thirty of the 32 enrolled subjects completed the study. Two Chinese men were withdrawn from the study, one due to a low platelet-rich plasma count after receipt of prasugrel 30 mg and the other due to mild, intermittent rectal bleeding after bowel movements that began ∼2 days after receipt of clopidogrel 300 mg. The mean IPA with prasugrel was significantly higher in Chinese than in white subjects at 0.5, 1, and 2 hours after dosing ( P < 0.05), but not at 4 or 24 hours. In Chinese subjects, mean maximal IPA (87%) occurred 1 hour after prasugrel dosing; in white subjects, mean maximal IPA (78%) occurred 2 hours after prasugrel dosing. In Chinese subjects, the mean IPA was significantly higher at all time points after administration of prasugrel 30 mg than after administration of clopidogrel 300 mg ( P <0.001). After administration of Clopidogrel 300 mg in Chinese subjects, mean maximal IPA (58%) occurred at 4 hours. The VN-P2Y12 and VASP phospho-rylation assays yielded results comparable to those obtained by LTA. Mean exposure to prasugrel's active metabolite was higher in Chinese than in white subjects (geometric least squares mean ratio for AUC 0−t = 1.47 (90% CI, 1.24–1.73). Both drugs were well tolerated. Conclusions: In this study, platelet inhibition was significantly higher in Chinese than in white subjects up to 2 hours after a single 30-mg dose of prasugrel. Platelet inhibition was significantly higher in Chinese subjects at all time points after a 30-mg dose of prasugrel than after a 300-mg dose of clopidogrel. Both treatments were generally well tolerated.

Genetic variation of CYP2C19 affects both pharmacokinetic and pharmacodynamic responses to clopidogrel but not prasugrel in aspirin-treated patients with coronary artery disease

AimsThe metabolic pathways leading to the formation of prasugrel and clopidogrel active metabolites differ. We hypothesized that decreased CYP2C19 activity affects the pharmacokinetic and pharmacodynamic response to clopidogrel but not prasugrel.Methods and resultsNinety-eight patients with coronary artery disease (CAD) taking either clopidogrel 600 mg loading dose (LD)/75 mg maintenance dose (MD) or prasugrel 60 mg LD/10 mg MD were genotyped for variation in six CYP genes. Based on CYP genotype, patients were segregated into two groups: normal function (extensive) metabolizers (EM) and reduced function metabolizers (RM). Plasma active metabolite concentrations were measured at 30 min, 1, 2, 4, and 6 h post-LD and during the MD period on Day 2, Day 14, and Day 29 at 30 min, 1, 2, and 4 h. Vasodilator-stimulated phosphoprotein (VASP) and VerifyNow™ P2Y12 were measured predose, 2, and 24 ± 4 h post-LD and predose during the MD period on Day 14 ± 3 and Day 29 ± 3. For clopidogrel, active metabolite exposure was significantly lower (P = 0.0015) and VASP platelet reactivity index (PRI, %) and VerifyNow™ P2Y12 reaction unit (PRU) values were significantly higher (P < 0.05) in the CYP2C19 RM compared with the EM group. For prasugrel, there was no statistically significant difference in active metabolite exposure or pharmacodynamic response between CYP2C19 EM and RM. Variation in the other five genes demonstrated no statistically significant differences in pharmacokinetic or pharmacodynamic responses.ConclusionVariation in the gene encoding CYP2C19 in patients with stable CAD contributes to reduced exposure to clopidogrel's active metabolite and a corresponding reduction in P2Y12 inhibition, but has no significant influence on the response to prasugrel.