D-dimer: simple test, tough problems.

CONTEXT: D-dimer is widely used for exclusion, or as an aid in diagnosis, of venous thromboembolism (VTE); however, the D-dimer assay methods available from manufacturers and the laboratory application of those methods vary widely. OBJECTIVES: To describe the current laboratory practice regarding the assay and reporting of D-dimer. DESIGN: Laboratories' D-dimer proficiency testing data were analyzed and laboratory practices regarding the performance and reporting of D-dimer were surveyed. RESULTS: Initial grading of D-dimer proficiency testing demonstrated high variability within and among methods. This variability continued to be present for several years after attempts to intervene. The number of laboratories using D-dimer to exclude VTE grew from 1500 in 2004 to more than 3500 in 2012. Survey and proficiency testing data demonstrated that 33% of laboratories changed the type or magnitude of units from that recommended by the manufacturer, a practice associated with as much as a 20-fold increase in the failure of proficiency testing. Many laboratories used a threshold for the exclusion of VTE that is higher than that recommended by the manufacturer. Many laboratories continue to use qualitative assays with insufficient sensitivity for exclusion of VTE. CONCLUSIONS: There is considerable variability both within and among quantitative methods used to assay D-dimer by laboratories. Laboratory practice continues to vary widely regarding the type and magnitude of units reported and the setting of the threshold for the exclusion of VTE. Although improved, the variability continues despite initial efforts to intervene.

Safety and pharmacokinetics of the antisense oligonucleotide (ASO) LY2181308 as a single-agent or in combination with idarubicin and cytarabine in patients with refractory or relapsed acute myeloid leukemia (AML).

Survivin is expressed in tumor cells, including acute myeloid leukemia (AML), regulates mitosis, and prevents tumor cell death. The antisense oligonucleotide sodium LY2181308 (LY2181308) inhibits survivin expression and may cause cell cycle arrest and restore apoptosis in AML. In this study, the safety, pharmacokinetics, and pharmacodynamics/efficacy of LY2181308 was examined in AML patients, first in a cohort with monotherapy (n = 8) and then post-amendment in a cohort with the combination of cytarabine and idarubicin treatment (n = 16). LY2181308 was administered with a loading dosage of three consecutive daily infusions of 750 mg followed by weekly intravenous (IV) maintenance doses of 750 mg. Cytarabine 1.5 g/m(2) was administered as a 4-hour IV infusion on Days 3, 4, and 5 of Cycle 1, and idarubicin 12 mg/m(2) was administered as a 30-minute IV infusion on Days 3, 4, and 5 of Cycle 1. Cytarabine and idarubicin were administered on Days 1, 2, and 3 of each subsequent 28-day cycle. Reduction of survivin was evaluated in peripheral blasts and bone marrow. Single-agent LY2181308 was well tolerated and survivin was reduced only in patients with a high survivin expression. In combination with chemotherapy, 4/16 patients had complete responses, 1/16 patients had incomplete responses, and 4/16 patients had cytoreduction. Nine patients died on study: 6 (monotherapy), 3 (combination). LY2181308 alone is well tolerated in patients with AML. In combination with cytarabine and idarubicin, LY2181308 does not appear to cause additional toxicity, and has shown some clinical benefit needing confirmation in future clinical trials.

Biomarkers of the Hedgehog/Smoothened pathway in healthy volunteers.

The Hedgehog (Hh) pathway is involved in oncogenic transformation and tumor maintenance. The primary objective of this study was to select surrogate tissue to measure messenger ribonucleic acid (mRNA) levels of Hh pathway genes for measurement of pharmacodynamic effect. Expression of Hh pathway specific genes was measured by quantitative real time polymerase chain reaction (qRT-PCR) and global gene expression using Affymetrix U133 microarrays. Correlations were made between the expression of specific genes determined by qRT-PCR and normalized microarray data. Gene ontology analysis using microarray data for a broader set of Hh pathway genes was performed to identify additional Hh pathway-related markers in the surrogate tissue. RNA extracted from blood, hair follicle, and skin obtained from healthy subjects was analyzed by qRT-PCR for 31 genes, whereas 8 samples were analyzed for a 7-gene subset. Twelve sample sets, each with ≤500 ng total RNA derived from hair, skin, and blood, were analyzed using Affymetrix U133 microarrays. Transcripts for several Hh pathway genes were undetectable in blood using qRT-PCR. Skin was the most desirable matrix, followed by hair follicle. Whether processed by robust multiarray average or microarray suite 5 (MAS5), expression patterns of individual samples showed co-clustered signals; both normalization methods were equally effective for unsupervised analysis. The MAS5- normalized probe sets appeared better suited for supervised analysis. This work provides the basis for selection of a surrogate tissue and an expression analysis-based approach to evaluate pathway-related genes as markers of pharmacodynamic effect with novel inhibitors of the Hh pathway.

Quantitative measurement of cell-free plasma DNA and applications for detecting tumor genetic variation and promoter methylation in a clinical setting.

An elevated cell-free DNA (cfDNA) level is often reported in patients with advanced cancer and is thought to represent nuclear material from a distant inaccessible tumor. cfDNA can become a valuable source to monitor tumor dynamics and evaluate genetic markers for predictive, prognostic, and diagnostic testing. DNA extraction and quantification were optimized with plasma collected from 20 patients with advanced cancer and 16 healthy controls. Plasma cfDNA from patients with advanced cancer was evaluated for TP53 genetic variation and methylation status of CpG islands in several promoters of known disease-related genes. Tumor biopsy and corresponding plasma specimens were collected from study participants to determine whether the same genetic variations were present in both samples. The cfDNA isolation method provided a lower DNA detection limit of 144 pg, equivalent to DNA from approximately 24 cells. Normal pooled human plasma cfDNA averaged 110 copies/mL of the ACTB gene. Extracted cfDNA was suitable for gene-specific variant detection, sequencing, and promoter methylation analysis. DNA extracted from tumor biopsy and corresponding plasma specimens from two patients with advanced cancer revealed an identical, nonsynonymous variant present in both samples. Immunohistochemical analysis confirmed the TP53 mutant phenotype in the tumor specimens. Quantitative measurement of cfDNA represents a useful biomarker to follow treatment outcome and is a valuable tool with which to characterize specific genetic alterations for both patient selection and personalized treatment.

Association of long-term administration of the survivin mRNA-targeted antisense oligonucleotide LY2181308 with reversible kidney injury in a patient with metastatic melanoma.

A 57-year-old man with metastatic melanoma was treated with the survivin inhibitor and antisense oligonucleotide LY2181308 as part of a First-in-Human Dose trial. After 18 months of treatment, he developed kidney injury and the treatment was discontinued. At 9 months and before the development of kidney injury, LY2181308 concentrations were 8- to 10-fold higher relative to median predicted values, but within the targeted exposure considered to be safe. However, at 17 months, 28 days after stopping LY2181308 therapy, LY2181308 concentration exceeded the predicted range by 38-fold. His decreased kidney function was slow to improve after stopping treatment. A kidney biopsy showed signs of acute tubular injury with regeneration. Complete recovery of kidney function occurred 6 months after treatment was stopped. The relationship between high exposures and slow LY2181308 clearance with the gradual improvement in kidney function after stopping the antisense treatment suggests that the oligonucleotide was related to the kidney injury. Based on this case report, kidney function should be monitored frequently in patients receiving long-term treatment with antisense oligonucleotides that specifically target survivin, particularly when they receive concomitant angiotensin-converting enzyme inhibitors or nonsteroidal anti-inflammatory drugs.

Inhibition of platelet aggregation with prasugrel and clopidogrel: an integrated analysis in 846 subjects.

This integrated analysis compared speed of onset, level of platelet inhibition, and response variability to prasugrel and clopidogrel in healthy subjects and in patients with stable coronary artery disease with data pooled from 24 clinical pharmacology studies. Data from subjects (N = 846) were categorized into the following treatment groups: prasugrel 60 mg loading dose (LD)/10 mg maintenance dose (MD), clopidogrel 300 mg LD/75 mg MD, or clopidogrel 600 mg LD/75 mg MDs. Maximum platelet aggregation (MPA) and inhibition of platelet aggregation (IPA) to 5 and 20 muM ADP were assessed by turbidimetric aggregometry. A linear mixed-effect model compared the MPA and IPA between treatments over time points evaluated in the integrated database, and covariates affecting platelet inhibition were identified. Prasugrel 60 mg LD resulted in faster onset, greater magnitude, and more consistent levels of inhibition of platelet function compared to either clopidogrel 300 mg or 600 mg LDs. Greater and more consistent levels of platelet inhibition were observed with the prasugrel 10 mg MD compared to the clopidogrel 75 mg MD. This integrated analysis confirms the findings of earlier individual studies, that prasugrel achieves faster onset of greater extent and more consistent platelet inhibition compared to the approved and higher loading doses of clopidogrel. Gender, race, body weight, and age were identified as statistically significant covariates impacting platelet inhibition.

Cytochrome P450 genetic polymorphisms and the response to prasugrel: relationship to pharmacokinetic, pharmacodynamic, and clinical outcomes.

BACKGROUND: Both clopidogrel and prasugrel require biotransformation to active metabolites by cytochrome P450 (CYP) enzymes. Among persons treated with clopidogrel, carriers of reduced-function CYP2C19 alleles have significantly lower levels of active metabolite, diminished platelet inhibition, and higher rates of adverse cardiovascular events. The effect of CYP polymorphisms on the clinical outcomes in patients treated with prasugrel remains unknown. METHODS AND RESULTS: The associations between functional variants in CYP genes, plasma concentrations of active drug metabolite, and platelet inhibition in response to prasugrel were tested in 238 healthy subjects. We then examined the association of these genetic variants with cardiovascular outcomes in a cohort of 1466 patients with acute coronary syndromes allocated to treatment with prasugrel in the Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition With Prasugrel-Thrombolysis in Myocardial Infarction 38 trial. Among the healthy subjects, no significant attenuation of the pharmacokinetic or the pharmacodynamic response to prasugrel was observed in carriers versus noncarriers of at least 1 reduced-function allele for any of the CYP genes tested (CYP2C19, CYP2C9, CYP2B6, CYP3A5, and CYP1A2). Consistent with these findings, in subjects with acute coronary syndromes treated with prasugrel, no significant associations were found between any of the tested CYP genotypes and risk of cardiovascular death, myocardial infarction, or stroke. CONCLUSIONS: Common functional CYP genetic variants do not affect active drug metabolite levels, inhibition of platelet aggregation, or clinical cardiovascular event rates in persons treated with prasugrel. These pharmacogenetic findings are in contrast to observations with clopidogrel, which may explain, in part, the different pharmacological and clinical responses to the 2 medications.

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

AIMS: The 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 RESULTS: Ninety-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 P2Y(12) 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. CONCLUSION: Variation in the gene encoding CYP2C19 in patients with stable CAD contributes to reduced exposure to clopidogrel's active metabolite and a corresponding reduction in P2Y(12) inhibition, but has no significant influence on the response to prasugrel.

Assessment of P2Y(12) inhibition with the point-of-care device VerifyNow P2Y12 in patients treated with prasugrel or clopidogrel coadministered with aspirin.

BACKGROUND: Variability in response to thienopyridines has led to the development of point-of-care devices to assess adenosine diphosphate (ADP)-induced platelet aggregation. These tests need to be evaluated in comparison to reference measurements of P2Y(12) function during different thienopyridine treatments. METHODS: After a run-in on 75 mg aspirin, 110 subjects were randomized to double-blind treatment with clopidogrel 600 mg loading dose (LD)/75 mg maintenance dose (MD) or prasugrel 60 mg LD/10 mg MD. Antiplatelet effects were evaluated by VerifyNow P2Y12 (VN-P2Y12) device (Accumetrics, San Diego, CA), vasodilator-stimulated phosphoprotein (VASP) phosphorylation assay, and light transmission aggregometry (LTA). Prasugrel's and clopidogrel's active metabolite concentration were also determined. RESULTS: Dose- and time-dependent inhibition of P2Y(12) was evident with VN-P2Y12. There was strong correlation with VN-P2Y12 and VASP or LTA for all treatments through a wide range of P2Y(12) function. At high levels of P2Y(12) inhibition, platelet function measured by VN-P2Y12 was maximally inhibited and could not reflect further changes seen with VASP or LTA methods. Correlation was also observed between exposure to clopidogrel's active metabolite and VN-P2Y12 during MD and LD, whereas it was observed only with prasugrel MD. CONCLUSION: The VN-P2Y12 correlated strongly with inhibition of P2Y(12) function, as measured with either VASP or LTA. VN-P2Y12 also correlated to exposure to the active metabolite of prasugrel and clopidogrel up to levels associated with assumed saturation of the P2Y(12) receptor.

Cytochrome p-450 polymorphisms and response to clopidogrel.

BACKGROUND: Clopidogrel requires transformation into an active metabolite by cytochrome P-450 (CYP) enzymes for its antiplatelet effect. The genes encoding CYP enzymes are polymorphic, with common alleles conferring reduced function. METHODS: We tested the association between functional genetic variants in CYP genes, plasma concentrations of active drug metabolite, and platelet inhibition in response to clopidogrel in 162 healthy subjects. We then examined the association between these genetic variants and cardiovascular outcomes in a separate cohort of 1477 subjects with acute coronary syndromes who were treated with clopidogrel in the Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel-Thrombolysis in Myocardial Infarction (TRITON-TIMI) 38. RESULTS: In healthy subjects who were treated with clopidogrel, carriers of at least one CYP2C19 reduced-function allele (approximately 30% of the study population) had a relative reduction of 32.4% in plasma exposure to the active metabolite of clopidogrel, as compared with noncarriers (P<0.001). Carriers also had an absolute reduction in maximal platelet aggregation in response to clopidogrel that was 9 percentage points less than that seen in noncarriers (P<0.001). Among clopidogrel-treated subjects in TRITON-TIMI 38, carriers had a relative increase of 53% in the composite primary efficacy outcome of the risk of death from cardiovascular causes, myocardial infarction, or stroke, as compared with noncarriers (12.1% vs. 8.0%; hazard ratio for carriers, 1.53; 95% confidence interval [CI], 1.07 to 2.19; P=0.01) and an increase by a factor of 3 in the risk of stent thrombosis (2.6% vs. 0.8%; hazard ratio, 3.09; 95% CI, 1.19 to 8.00; P=0.02). CONCLUSIONS: Among persons treated with clopidogrel, carriers of a reduced-function CYP2C19 allele had significantly lower levels of the active metabolite of clopidogrel, diminished platelet inhibition, and a higher rate of major adverse cardiovascular events, including stent thrombosis, than did noncarriers.

Patients with poor responsiveness to thienopyridine treatment or with diabetes have lower levels of circulating active metabolite, but their platelets respond normally to active metabolite added ex vivo.

OBJECTIVES: We evaluated the prevalence and mechanism of poor responsiveness to clopidogrel and prasugrel in coronary artery disease patients with and without diabetes. BACKGROUND: Low platelet inhibition by clopidogrel is associated with ischemic clinical events. A higher 600-mg loading dose (LD) has been advocated to increase responsiveness to clopidogrel. METHODS: In this study, 110 aspirin-treated patients were randomized to double-blind treatment with clopidogrel 600 mg LD/75 mg maintenance dose (MD) for 28 days or prasugrel 60 mg LD/10 mg MD for 28 days. Pharmacodynamic (PD) response was evaluated by light transmission aggregometry and vasodilator-stimulated phosphoprotein phosphorylation. The PD poor responsiveness was defined with 4 definitions previously associated with worse clinical outcomes. Active metabolites (AM) of clopidogrel and prasugrel were measured. Clopidogrel AM was added ex vivo. RESULTS: The proportion of patients with poor responsiveness was greater in the clopidogrel group for all definitions at all time points from 1 h to 29 days. Poor responders had significantly lower plasma AM levels compared with responders. Patients with diabetes were over-represented in the poor-responder groups and had significantly lower levels of AM. Platelets of both poor responders and diabetic patients responded fully to AM added ex vivo. CONCLUSIONS: Prasugrel treatment results in significantly fewer PD poor responders compared with clopidogrel after a 600-mg clopidogrel LD and during MD. The mechanism of incomplete platelet inhibition in clopidogrel poor-responder groups and in diabetic patients is lower plasma levels of its AM and not differences in platelet P2Y(12) receptor function.

Effect of atorvastatin on the pharmacokinetics and pharmacodynamics of prasugrel and clopidogrel in healthy subjects.

STUDY OBJECTIVE: To investigate the potential effect of atorvastatin 80 mg/day on the pharmacokinetics and pharmacodynamics of the thienopyridines prasugrel and clopidogrel. DESIGN: Open-label, randomized, crossover, two-arm, parallel-group study. SETTING: Single clinical research center in the United Kingdom. PARTICIPANTS: Sixty-nine healthy men aged 18-60 years. Intervention. Subjects received either a loading dose of prasugrel 60 mg followed by a maintenance dose of 10 mg/day or a loading dose of clopidogrel 300 mg followed by 75 mg/day. The drug was given as monotherapy for 10 days, and after a 6-day run-in period with atorvastatin 80 mg/day, the same dosage of atorvastatin was continued with the respective thienopyridine for 10 days. A 14-day washout period separated the treatment regimens. MEASUREMENTS AND MAIN RESULTS: Blood samples were collected before and at various time points after dosing on days 1 and 11 for determination of plasma concentrations of metabolites and for measurement of platelet aggregation induced by adenosine 5'-diphosphate 20 microM and vasodilator-stimulated phosphoprotein (VASP). Coadministration of atorvastatin did not alter exposure to active metabolites of prasugrel or clopidogrel after the loading dose and thus did not alter inhibition of platelet aggregation (IPA). During maintenance dosing, atorvastatin administration resulted in 17% and 28% increases in the area under the plasma concentration-time curve (AUC) values of prasugrel's and clopidogrel's active metabolites, respectively. These small changes in AUC did not result in a significant change in IPA response to prasugrel but did result in a significant increase in IPA during clopidogrel maintenance dosing at some, but not all, of the time points on day 11. Coadministration of atorvastatin with either prasugrel or clopidogrel had no effect on VASP phosphorylation relative to the thienopyridine alone after the loading dose. CONCLUSION: Coadministration of atorvastatin 80 mg/day with prasugrel or clopidogrel did not negatively affect the antiplatelet response to either drug after a loading dose or during maintenance dosing. The lack of a clinically meaningful effect of high-dose atorvastatin on the pharmacodynamic response to prasugrel after the loading or maintenance dose indicates that no dosage adjustment should be necessary in patients receiving these drugs concomitantly.

Greater reduction of platelet activation markers and platelet-monocyte aggregates by prasugrel compared to clopidogrel in stable coronary artery disease.

Prasugrel, a novel P2Y(12) ADP-receptor antagonist, has been reported to achieve greater inhibition of platelet aggregation compared to clopidogrel as assessed by light transmission aggregometry. It was the objective of this study to investigate the effect of prasugrel on alternative markers of platelet activation in comparison to a high loading dose and the approved maintenance dose of clopidogrel. One hundred ten aspirin-treated patients with stable coronary artery disease were randomized to a loading dose (LD, day 1)/ maintenance dose (MD, days 2-29) of prasugrel 60 mg/10 mg or clopidogrel 600 mg/75 mg. Platelet activation markers were analyzed by whole blood flow cytometry pre-dose and at 2 and 24 hours after LD and pre-dose at 14 and 29 days. After stimulation with 20 muM ADP, 2 hours after LD, significantly lower expression of activated GPIIb/IIIa (4.3 vs. 21.8 [mean fluorescent intensity (MFI)], p < 0.001) and P-selectin (2.0 vs. 11.7 MFI, p < 0.001) along with decreased formation of platelet-monocyte aggregates (16.4% vs. 29.6% positive cells, p < 0.001) was observed with prasugrel versus clopidogrel. All these effects were maintained through 24 hours and during the MD period. In conclusion, prasugrel 60 mg LD and 10 mg MD inhibit several markers of platelet activation and the formation of platelet-monocyte aggregates more effectively than a 600 mg LD and 75 mg MD of clopidogrel. Attenuated platelet aggregation and reduced expression of platelet pro-coagulant and pro-inflammatory markers with prasugrel suggest the potential to reduce cardiovascular events both in the acute setting and in long-term treatment.

Switching directly to prasugrel from clopidogrel results in greater inhibition of platelet aggregation in aspirin-treated subjects.

Prasugrel, a novel P2Y(12) antagonist, achieves faster onset and greater inhibition of platelet aggregation than clopidogrel 300 and 600 mg loading doses (LD). We studied the safety, time course, and level of platelet inhibition when switching directly from clopidogrel 75 mg maintenance dose (MD) to a prasugrel 60 mg LD/10 mg MD or 10 mg MD regimen. Healthy subjects (n = 39) on aspirin (81 mg/d) received a clopidogrel 600 mg LD followed by 10 days of clopidogrel MD (75 mg/d). Subjects were then randomized without a washout period to prasugrel 60 mg LD (n = 16) followed by 10 days of prasugrel MD (10 mg/d) or to prasugrel MD (10 mg/d, n = 19) for 11 days. Maximal platelet aggregation (MPA) to 20 microM ADP was measured by turbidimetric aggregometry. In subjects on clopidogrel 75 mg MD, mean MPA decreased from 39 to 12% by 30 minutes, and to 5% by 1 hour after a prasugrel 60 mg LD (p < 0.001 for both) and from 37 to 28% (p < 0.001) by 1 hour after a prasugrel 10 mg MD. During prasugrel MD, a new pharmacodynamic steady state MPA of approximately 24% (p < 0.01 vs. clopidogrel MD) occurred within four to five days of switching from clopidogrel. Changing from clopidogrel to prasugrel did not increase bleeding episodes or other adverse events. Switching directly from clopidogrel MD to either prasugrel LD or MD was well tolerated and resulted in significantly greater levels of platelet inhibition than a clopidogrel 75 mg MD.

Effects of the proton pump inhibitor lansoprazole on the pharmacokinetics and pharmacodynamics of prasugrel and clopidogrel.

Prasugrel and clopidogrel, thienopyridine prodrugs, are each metabolized to an active metabolite that inhibits the platelet P2Y(12) ADP receptor. In this open-label, 4-period crossover study, the effects of the proton pump inhibitor lansoprazole on the pharmacokinetics and pharmacodynamics of prasugrel and clopidogrel were assessed in healthy subjects given single doses of prasugrel 60 mg and clopidogrel 300 mg with and without concurrent lansoprazole 30 mg qd. C(max) and AUC(0-tlast) of prasugrel's active metabolite, R-138727, and clopidogrel's inactive carboxylic acid metabolite, SR26334, were assessed. Inhibition of platelet aggregation (IPA) was measured by turbidimetric aggregometry 4 to 24 hours after each treatment. Lansoprazole (1) decreased R-138727 AUC(0-tlast) and C(max) by 13% and 29%, respectively, but did not affect IPA after the prasugrel dose, and (2) did not affect SR62334 exposure but tended to lower IPA after a clopidogrel dose. A retrospective tertile analysis showed in subjects with high IPA after a clopidogrel dose alone that lansoprazole decreased IPA, whereas IPA was unaffected in these same subjects after a prasugrel dose. The overall data suggest that a prasugrel dose adjustment is not likely warranted in an individual taking prasugrel with a proton pump inhibitor such as lansoprazole.

The use of the VerifyNow P2Y12 point-of-care device to monitor platelet function across a range of P2Y12 inhibition levels following prasugrel and clopidogrel administration.

Variability in response to antiplatelet agents has prompted the development of point-of-care (POC) technology. In this study, we compared the VerifyNow P2Y12 (VN-P2Y12) POC device with light transmission aggregometry (LTA) in subjects switched directly from clopidogrel to prasugrel. Healthy subjects on aspirin were administered a clopidogrel 600 mg loading dose (LD) followed by a 75 mg/d maintenance dose (MD) for 10 days. Subjects were then switched to a prasugrel 60 mg LD and then 10 mg/d MD for 10 days (n = 16), or to a prasugrel 10 mg/d MD for 11 days (n = 19). Platelet function was measured by LTA and VN-P2Y12 at baseline and after dosing. Clopidogrel 600 mg LD/75 mg MD treatment led to a reduction in P2Y(12) reaction units (PRU) from baseline. A switch from clopidogrel MD to prasugrel 60 mg LD/10 mg MD produced an immediate decrease in PRU, while a switch to prasugrel 10 mg MD resulted in a more gradual decline. Consistent with the reduction in PRU, device-reported percent inhibition increased during both clopidogrel and prasugrel regimens. Inhibition of platelet aggregation as measured by LTA showed a very similar pattern to that found with VN-P2Y12 measurement, irrespective of treatment regimens. The dynamic range of VN-P2Y12 appeared to be narrower than that of LTA. With two different thienopyridines, the VN-P2Y12 device, within a somewhat more limited range, reflected the overall magnitude of change in aggregation response determined by LTA. The determination of the clinical utility of such POC devices will require their use in clinical outcome studies.

A comparison of the antiplatelet effects of prasugrel and high-dose clopidogrel as assessed by VASP-phosphorylation and light transmission aggregometry.

Platelet inhibition as measured by vasodilator-stimulated phosphoprotein (VASP) and light transmission aggregometry (LTA) have shown concordance following dosing of clopidogrel. No reports have directly compared the VASP assay and LTA at the levels of P2Y(12) blockade after loading doses (LDs) of prasugrel or high dose clopidogrel (600 and 900 mg). The aim was to compare the VASP assay and LTA during the loading dose phase of a comparative study of prasugrel and clopidogrel. Prasugrel 60 mg LD/10 mg maintenance dose (MD) and clopidogrel 300 mg/75 mg and 600 mg/75 mg LD/MD regimens were compared in a 3-way crossover study in 41 healthy, aspirin-free subjects. Each LD was followed by seven daily MDs and a 14-day washout period. P2Y(12) receptor blockade was estimated using the VASP assay, expressed as platelet reactivity index (VASP-PRI). Platelet aggregation was assessed by light transmission aggregometry (20 and 5 microM ADP). Twenty-four hours after prasgurel 60 mg or clopidogrel 300 mg and 600 mg, respectively, VASP-PRI decreased from approximately 80% to 8.9%, 54.7%, and 39.0%, and maximal platelet aggregation (MPA) decreased from approximately 79% to 10.8%, 42.7%, and 31.2%, with an overall VASP:MPA correlation of 0.88 (p < 0.01). VASP assay responses after the clopidogrel LDs showed a wider range of values (300 mg: 0-93%; 600 mg: 0-80%) than prasugrel (0-13%); MPA responses followed a similar trend. Pearson's correlation suggested a strong agreement between VASP and LTA (20 microM ADP) for MPA (r = 0.86, p < 0.0001). VASP and LTA demonstrated concordance across the response range of P2Y(12) receptor blockade following thienopyridine LDs.

Increased active metabolite formation explains the greater platelet inhibition with prasugrel compared to high-dose clopidogrel.

Prasugrel pharmacodynamics and pharmacokinetics after a 60-mg loading dose (LD) and daily 10-mg maintenance doses (MD) were compared in a 3-way crossover study to clopidogrel 600-mg/75-mg and 300-mg/75-mg LD/MD in 41 healthy, aspirin-free subjects. Each LD was followed by 7 days of daily MD and a 14-day washout period. Inhibition of platelet aggregation (IPA) was assessed by turbidometric aggregometry (20 and 5 microM ADP). Prasugrel 60-mg achieved higher mean IPA (54%) 30 minutes post-LD than clopidogrel 300-mg (3%) or 600-mg (6%) (P < 0.001) and greater IPA by 1 hour (82%) and 2 hours (91%) than the 6-hour IPA for clopidogrel 300-mg (51%) or 600-mg (69%) (P < 0.01). During MD, IPA for prasugrel 10-mg (78%) exceeded that of clopidogrel (300-mg/75-mg, 56%; 600-mg/75-mg, 52%; P < 0.001). Active metabolite area under the concentration-time curve (AUC0-tlast) after prasugrel 60-mg (594 ng.hr/mL) was 2.2 times that after clopidogrel 600-mg. Prasugrel active metabolite AUC0-tlast was consistent with dose-proportionality from 10-mg to 60-mg, while clopidogrel active metabolite AUC0-tlast exhibited saturable absorption and/or metabolism. In conclusion, greater exposure to prasugrel's active metabolite results in faster onset, higher levels, and less variability of platelet inhibition compared with high-dose clopidogrel in healthy subjects.

Laboratory reporting of the international normalized ratio: progress and problems.

CONTEXT: The international normalized ratio (INR) is widely used to monitor oral anticoagulation and to evaluate patients with coagulation disorders. OBJECTIVE: To examine the variability of the performance and reporting of the INR and to evaluate laboratory calculation of the INR. DESIGN: Between 1993 and 2003, laboratories participating in proficiency testing were surveyed. Participants provided the international sensitivity index and the mean normal prothrombin time used to calculate the INR. The INR was calculated from the data provided and compared with the INR reported to determine if the calculation was correct. RESULTS: Survey data regarding the INR collected between 1993 and 2003 demonstrate an improvement in reporting, using appropriate anticoagulant, using lower international sensitivity index reagents, and matching international sensitivity index and prothrombin time method. The all-method coefficient of variation of the INR improved from 18% to 5.8%. Among 3813 laboratories studied in 2002 and 2003, 4.1% miscalculated INR. Of 29 laboratories that reported investigation of the INR miscalculation, 11 (38%) reported correcting an INR that was being reported in patient results and that this error was corrected as a result of the study. Since beginning grading of the INR calculation, miscalculation of the INR has fallen to less than 1%. CONCLUSIONS: Recommendations for change in laboratory practice made by consensus conferences are implemented during the course of many years. Difficulty calculating the INR was documented, and both the calculation and the variability in the reporting of the INR showed improvement. Proficiency testing, when closely evaluated and acted on, can have a direct impact on the quality of patient care.

Greater inhibition of platelet aggregation and reduced response variability with prasugrel versus clopidogrel: an integrated analysis.

Multiple studies report response variability to a 300-mg clopidogrel loading dose (LD). Pooled platelet aggregometry data compared responses (change in maximal platelet aggregation [DeltaMPA] or inhibition of platelet aggregation [IPA]) to clopidogrel 300-mg (n = 131) or prasugrel 60-mg (n = 109) LDs. Poor responder rates were determined using empiric criteria (IPA < 10% and DeltaMPA < 10% for 20 microM and 5 microM adenosine diphosphate [ADP]) and Bayesian model-based criteria (IPA < 20% and DeltaMPA < 15% for 20 microM ADP; IPA < 25% and DeltaMPA < 20% for 5 microM ADP). Prasugrel achieved greater DeltaMPA and IPA from 2 to 24 hours post-LD (P < .001). For 20 microM ADP, poor responder rates for clopidogrel ranged from 17% to 43%; no prasugrel poor responders were observed. Regardless of the criterion, prasugrel 60 mg achieved greater IPA and fewer poor responders than the clopidogrel 300-mg LD.