Interaction between acetaminophen and warfarin in adults receiving long-term oral anticoagulants: a randomized controlled trial.

PURPOSE: We investigated whether acetaminophen, given at 2 g/day and 3 g/day might potentiate the anticoagulant effect of warfarin. METHODS: Forty-five patients on stable warfarin therapy, enrolled in this prospective, randomized, parallel (three arms), placebo-controlled study, received a 10-day regimen of acetaminophen (2 g/day or 3 g/day) or placebo. RESULTS: The mean maximal INR increase was 0.70 ± 0.49 and 0.67 ± 0.62 in patients receiving acetaminophen at 2 g/day and 3 g/day, respectively (P=0.01 for the respective comparisons versus placebo). The INR increase became significant on day 3 and was independently and significantly predicted by a maximal decrease in factor II (R(2)=0.36, P<0.0001), factor VII (R (2)=0.46, P<0.0001) and a maximal increase in acetaminophen plasma concentrations (R(2)=0.563, P<0.0001). CONCLUSION: Acetaminophen, at 2 g/day or 3 g/day, enhanced the anticoagulant effect of warfarin in stable patients, thus requiring close INR monitoring in the clinical setting.

Is platelet function testing at the acute phase under P2Y12 inhibitors helpful in predicting bleeding in real-life patients with acute coronary syndrome? The AVALANCHE study.

BACKGROUND: In patients with acute coronary syndrome (ACS), current international guidelines recommend newer potent and predictable P2Y12 inhibitors as first-line treatment despite a greater bleeding risk compared with clopidogrel. AIM: To determine if platelet function testing can predict bleeding in real-life patients with ACS treated with newer P2Y12 inhibitors. METHODS: In this retrospective study, all consecutive adults admitted to the Lariboisière University Hospital for ACS, whatever the P2Y12 inhibitor prescribed, who had platelet function testing (vasodilator-stimulated phosphoprotein phosphorylation [VASP] index and aggregation tests) during the initial hospital stay were included. Follow-up was performed to record bleeding events according to the Bleeding Academic Research Consortium (BARC) classification. RESULTS: A total of 364 patients were included, treated with ticagrelor (n=123), prasugrel (n=105) or clopidogrel (n=136); 42.3% after an ST-segment elevation myocardial infarction, 27.1% after a non-ST-segment elevation myocardial infarction and 30.6% with unstable angina. Mean age was 64±11 years. Median VASP index was significantly lower with the newer P2Y12 inhibitors (14% under ticagrelor, 14% under prasugrel) than with clopidogrel (42%). Despite these differences in the degree of platelet inhibition, the occurrence of bleeding (BARC 2-5) during follow-up was 7.7% overall, and was similar for all P2Y12 inhibitors (ticagrelor 8.9%; prasugrel 6.6%; clopidogrel 7.4%). For each P2Y12 inhibitor, it was impossible to determine a VASP index threshold under which bleeding was significantly greater during follow-up. Similarly, ADP-induced aggregation was more profoundly inhibited by ticagrelor and prasugrel than by clopidogrel, but this did not allow a threshold to be set for increased haemorrhagic risk. CONCLUSIONS: Despite the substantial occurrence of bleeding in patients with ACS during follow-up, neither the VASP index nor platelet aggregation test results measured at the acute phase were helpful in predicting bleeding risk. Whether platelet function testing could be helpful later in the course of treatment remains to be evaluated.

Functional variability of platelet response to clopidogrel correlates with P2Y(12) receptor occupancy.

Interindividual variability of response to clopidogrel is currently a subject of much interest. We tested the hypothesis that functional variability in the platelet response to clopidogrel correlates with occupancy of the platelet P2Y(12) receptor by clopidogrel active metabolite. Healthy subjects were screened after seven days' treatment with clopidogrel 75 mg/day to select three clopidogrel-response groups (n = 12/group), defined as 'average' (40-60% inhibition of platelet aggregation [IPA]), 'low' (<10% IPA) or 'high' (>80% IPA) responders. After a two- to six-week wash-out period, subjects were randomized (double-blind) to clopidogrel 75 mg/day (n = 10/group) for 10 days, followed by clopidogrel 300 mg on day 11, or placebo (n = 2/group). IPA induced by adenosine diphosphate (ADP), and P2Y(12) receptor occupancy were measured repeatedly. The incidence of low responders was 3.7%, and low responses to clopidogrel were maintained during the randomized evaluation phase. Treatment with clopidogrel for 10 days induced a significant increase in P2Y(12) receptor occupancy in each group of responders versus placebo; receptor affinity was unchanged. This reduction correlated with IPA response (r = 0.54). The additional 300 mg dose of clopidogrel on top of 75 mg chronic treatment increased IPA and P2Y(12) receptor occupancy in all groups, but relatively more in low responders. Variability in the response to clopidogrel appears to be linked to differences in P2Y(12) receptor occupancy. An additional 300 mg dose of clopidogrel improves both IPA and P2Y(12) receptor occupancy mostly in the subset of 'low' responders.

A novel experimental thrombotic myocardial infarction and primary angioplasty model in swine.

AIMS: We sought to develop a reproducible animal model for acute myocardial infarction (AMI) in adult atherosclerosis-prone pigs. METHODS AND RESULTS: A coil was placed in the right coronary artery or the left anterior descending artery in 26 downsized spontaneously hypercholesterolaemic pigs and left untreated until thrombotic occlusion. Then, we crossed the thrombotic occlusion with a guidewire, followed by predilatation, thrombus visualisation with optical coherence tomography (OCT) imaging and, finally, deployment of a stent and repeated OCT. After revascularisation, we calculated the index of microcirculatory resistance (IMR). After a feasibility phase (six animals), acute thrombotic occlusion was achieved in all 20 pigs. Eighteen animals were successfully revascularised and survived until sacrifice. Thrombus formation was confirmed by OCT, measurement of thrombin-antithrombin complexes and pathology examination. Myocardial necrosis was confirmed by troponin T elevation, myocardial staining and pathology examination. Distal thrombotic embolisation and microvascular obstruction were supported by increased IMR and pathology examination. CONCLUSIONS: A porcine model of thrombotic occlusion AMI in miniaturised adult spontaneously atherosclerosis-prone pigs is feasible by percutaneous intracoronary placement of a coil. The reperfusion by angioplasty completed this model which mirrors human pathological conditions with myocardial infarction, necrosis and distal embolisation.

Enoxaparin chains stored during chronic treatment are mobilized by a bolus of unfractionated heparin: insights from the STACKENOX study.

The initial STACKENOX (STACK-on to ENOXaparin) study investigated the effect of stacking unfractionated heparin (UFH) onto a chronic treatment with enoxaparin, a common practice in interventional cardiology when a patient treated with enoxaparin receives an additional bolus of UFH at the time of percutaneous coronary intervention. The study brought to light some unexpected consequences on coagulation tests and hemorrhagic risk. This substudy was performed to provide a pharmacological explanation for these observations. Seventy-two healthy individuals previously treated with enoxaparin for 2.5 days received a stack-on of 70 IU/kg intravenous UFH dose 4, 6, or 10 h after the last enoxaparin dose. Anticoagulation activity was monitored by activated partial thromboplastin time, anti-Xa and anti-IIa activities and a thrombin generation test. In parallel, plasma samples of the individuals receiving the chronic enoxaparin treatment obtained at 4, 6, or 10 h after the last enoxaparin dose were spiked in vitro with a dose of UFH reproducing the concentration achieved in vivo after the bolus of UFH alone. In-vivo stack-on of UFH induced an over-anticoagulation identified by changes in anti-Xa and, less markedly, in anti-IIa and activated partial thromboplastin time levels, whereas in-vitro UFH spiking, only produced an additive effect. We hypothesize that the potentiation of UFH on anti-Xa activity observed in vivo may caused by the UFH bolus mobilizing enoxaparin chains stored in the endothelial glycocalyx during chronic pretreatment. This over-anticoagulation and its potential hemorrhagic risk after stack-on of UFH have obvious clinical implications.

Accuracy of point of care coagulometers compared to reference laboratory measurements in patients on oral anticoagulation therapy.

BACKGROUND: Vitamin K antagonists (VKA) are widely prescribed throughout the world. Patients on VKA therapy require international normalized ratio (INR) monitoring of venous blood to ensure the response remains within the therapeutic window. Point-of-care devices (POC-INR) can safely and easily monitor VKA efficacy but need to be evaluated in practice. The aim of this study was to assess the precision and accuracy of a new POC-INR (Qlab) compared to the laboratory plasma technique and the CoaguChek-XS system. METHODS: Consecutive patients on VKA referred to our institution were included. The study was designed to analyze 75 patients divided equally in the following subgroups: INR<2; INR=2-3; INR>3. INR was measured with an established laboratory method (INRREF) with an international sensitivity index of 1.0 and by two different POC-INRs: the Qlab (INRQlab) and the CoaguChek-XS systems (INRXS). RESULTS: 82 patients treated mainly for atrial fibrillation or venous thromboembolism disease were included. Precision in therapeutic range (INR=2-3) of both POC-INRs was satisfactory with a coefficient of variation of 4.6% for the Qlab and 4.3% for the CoaguChek-XS. INRRef was 2.70 ± 1.36, INRQlab 2.59 ± 1.25 and INRXS 2.89 ± 1.37. Accuracy was low with the Qlab (R(2)=0.64) and higher with the CoaguChek-XS (R(2)=0.94). The mean relative difference from the INRRef was higher for the Qlab (18.4%) than for the CoaguChek-XS (12.9%). Clinical concordance was lower with the Qlab (78.2%) than with the CoaguChek-XS (90.0%). CONCLUSION: This study suggests that the Qlab has accuracy limitations with clinical consequences. New POC-INR devices require careful evaluation prior to clinical implementation.

Reduced thrombus cohesion in an ex vivo human model of arterial thrombosis induced by clopidogrel treatment: kinetics of the effect and influence of single and double loading-dose regimens.

OBJECTIVE: To compare the effects of clopidogrel on ex vivo thrombogenesis with those on ADP-dependent platelet aggregation, and to compare single and double loading-dose regimens. METHODS AND RESULTS: Step 1: Volunteers (n=12) received clopidogrel 75 mg/day for 8 days. ADP-induced platelet aggregation was measured in platelet-rich plasma (PRP). Thrombogenesis was measured in an ex vivo model. Clopidogrel produced rapid platelet inhibition, increasing up to day 5. Maximal intensity of platelet aggregation correlated with density of platelet thrombus, surface of collagen covered by platelets and thrombus cross-sectional surface (p<0.001). Step 2: On day 1, volunteers (n=60) randomly received clopidogrel 75 mg, a single 300-mg loading dose or two 300-mg loading doses separated by a 12-h interval. On day 2, all volunteers received clopidogrel 75 mg. Both loading dose regimens enhanced platelet inhibition at all time points (p<0.03 vs. clopidogrel 75 mg). After 3 h, the antiplatelet effect of a loading dose was substantial, and the mean decrease in dense thrombus surface was greater in the loading-dose groups than in the 75 mg group (p=0.041 for the single loading dose). Ex vivo, there were no significant differences between loading-dose groups. CONCLUSIONS: Clopidogrel reduces arterial thrombus cohesion by an effect that correlates with inhibition of ADP-induced platelet aggregation. A single 300-mg loading dose provides a rapid onset of such an antithrombotic effect, which was more significant at 24 h with the double loading dose.

Differential sensitivity and kinetics of response of different ex vivo tests monitoring functional variability of platelet response to clopidogrel.

We previously showed that variability of response to clopidogrel is linked to occupancy of the P2Y12 receptor by clopidogrel active-metabolite, and that maximal platelet aggregation intensity (MAI) measured by light transmission aggregometry (LTA) correlates with occupancy. The present study compared a range of ex vivo platelet tests at various levels of P2Y12 occupancy. After screening with clopidogrel 75 mg/day for seven days, subjects were selected to obtain 'low', 'average' and 'high' responders and randomised to clopidogrel (75 mg/day days 1-10; 300 mg day 11), or placebo. Assays were LTA in platelet-rich plasma using 2, 5 and 20 mM ADP, VerifyNow P2Y12, flow cytometric analysis of platelet activation markers and vasodilator-stimulated phosphoprotein (VASP) index, and a thromboelastographic test that is sensitive to clopidogrel. The reference test was P2Y12 receptor occupancy, measured by binding of 33P-2MeS-ADP to platelets. MAI showed the best correlation with P2Y12 occupancy. Similar results were seen with different ADP concentrations and when LTA data were expressed as inhibition of platelet aggregation. A plot of free receptors/cell versus VASP index was biphasic, with poor correlation for low-level P2Y12 occupancy. Sensitivity of the VerifyNow P2Y12 assay decreased at higher clopidogrel responses. Thromboelastography and P-selectin expression had poor correlation with receptor occupancy. In conclusion, LTA data correlate best with P2Y12 occupancy, the gold standard for detecting clopidogrel's effect at the receptor level. Our results highlight a limitation of the VASP index, which appears unable to distinguish low, average and high responders early after clopidogrel initiation when P2Y12 occupancy is still low.

Wine constituents inhibit thrombosis but not atherogenesis in C57BL/6 apolipoprotein E-deficient mice.

Regular and moderate wine consumption is one of the explanations suggested for the lower incidence of cardiovascular events in France compared with other industrialized countries. We evaluated whether alcohol alone or combined with red wine polyphenols reduced plaque size and/or attenuated thrombotic reactivity at the site of advanced atherosclerotic lesions. Red wine extract, or purified (+)-catechin with alcohol, or alcohol alone, was added for 12 weeks to the drinking water of apoE-deficient (apoE(-/-)) C57BL/6 mice and wild-type counterparts. In the apoE(-/-) mice, all alcohol-containing mixtures were associated with a larger size of aortic atherosclerotic lesions. On the other hand, red wine extract and (+)-catechin significantly inhibited blood thrombotic reactivity (P<0.05) as assessed in a cylindrical perfusion chamber model of experimental thrombosis: area reductions in cross-sectional surface of the ex vivo thrombus were 64% and 63%, respectively. In the wild-type mice, red wine extract and (+)-catechin tended to reduce thrombogenicity, which was on the whole less marked than in the apoE(-/-) mice. These findings suggest that a moderate and regular consumption of red wine may protect against clinical cardiovascular events, mainly by attenuating the thrombogenic response rather than by reducing the development of atherosclerotic lesions. This antithrombogenic effect may include normalization of the abnormally high thrombogenic responsiveness in apoE(-/-) mice as well as a direct antithrombotic effect.