Low-dose aspirin for the prevention of atherothrombosis

Pharmacological interventions for peripheral artery disease

Peripheral arterial disease (PAD) encompasses the vascular diseases caused primarily by atherosclerosis and thromboembolic pathophysiological processes that alter the normal structure and function of the aorta, its visceral arterial branches and the arteries of the upper and lower extremities. PAD is associated with an increased risk for cardiovascular morbidity and mortality. The goals for pharmacological therapy in PAD should focus on reducing cardiovascular risk, improving walking distance and preventing critical limb ischaemia. Exercise training plays a key role in the therapeutic assessment, as well stopping smoking. Antiplatelet therapy (aspirin) should be given to every PAD patient if there are no contraindications. Neither their combination nor anticoagulant therapy has shown additional benefit in PAD patients. Several pharmacological agents have been developed to improve the functional state of the claudicant and to relieve the symptoms. Many studied drugs have shown either no, a small or a potential benefit. With future development of new drugs for PAD, there is an absolute need for very strict well-designed protocols in order to evaluate the claudication distance, the progression of the disease and the reduction in cardiovascular morbidity and mortality. New developments should focus on improvement of endothelial function, vascular repair and enhancement of collateral circulation.

New Antiplatelet Strategies in Atherothrombosis and Their Indications

Antiplatelet agents (APA) are used to reduce the risk of major cardiovascular events in various settings. When used for secondary prevention, antiplatelet monotherapy is associated with a relative risk reduction of such ischemic events of 25% compared to a placebo. New strategies are based on dual APA therapy. Aspirin-clopidogrel combination therapy is effective in situations of acute vessel injury such as myocardial infarction, coronary stenting and, possibly, peripheral stenting. GPIIb/IIIa inhibitors and loading doses of clopidogrel also have a place in these acute settings. In contrast, the aspirin-clopidogrel combination has proven disappointing in stable patients with cardiovascular disease, with no beneficial effect and, often, more bleeding events. Combination therapy with aspirin and extended-release dipyridamole may be more beneficial than very low doses of aspirin in ischemic stroke, but its use is limited by adverse effects. Overall, aspirin remains the first-line monotherapy of choice for patients with atherothrombosis, while clopidogrel is a valuable alternative. New antiplatelet strategies are in the pipeline, and clinically relevant laboratory tests of APA response may soon help to tailor treatment.

Contemporary use of clopidogrel in patients with coronary artery disease

Antiplatelet agents have long served as the cornerstone of pharmacologic therapy to prevent atherothrombotic events. The thienopyridines have risen to prominence as both an alternative and adjunctive treatment to aspirin monotherapy. These agents prevent platelet aggregation by selectively and irreversibly blocking the platelet ADP P2Y12 receptor. In this article we focus on the use of clopidogrel in the contemporary management of coronary artery disease. We assess the use of clopidogrel following revascularization for coronary artery disease with percutaneous coronary intervention, particularly after deployment of drug-eluting stents. Finally, we address some aspects of clopidogrel resistance.

Selective COX-2 inhibitors, eicosanoid synthesis and clinical outcomes: a case study of system failure

Elucidation of differences between the active sites of COX-1 and COX-2 allowed the targeted design of the selective COX-2 inhibitors known as coxibs. They were marketed as non-steroidal anti-inflammatory drugs (NSAIDs) that had improved upper gastrointestinal (GI) safety compared with older non-selective NSAIDs such as diclofenac and naproxen. Two GI safety studies conducted with arthritis patients demonstrated that in terms of upper GI safety, celecoxib was not superior to diclofenac (CLASS study) but rofecoxib was superior to naproxen (VIGOR study). However, the VIGOR study revealed also that rofecoxib had increased cardiovascular (CV) risk compared with naproxen. This clinical outcome was supported by the existence of plausible eicosanoid-based biological mechanisms whereby selective COX-2 inhibition could increase CV risk. Nevertheless, the existence of CV risk with rofecoxib was successfully discounted by its pharmaceutical company owner, Merck & Co, with the assistance of specialist opinion leaders and rofecoxib achieved widespread clinical use for 4-5 years. Rofecoxib was withdrawn from the market when several clinical trials in colorectal cancer and post-operative pain revealed increased CV risk with not only rofecoxib, but also coxibs. The commercial success of rofecoxib provides a case-study of failure of the medical journal literature to guide drug usage. Attention to ethical issues may have provided a more useful guide for prescribers.

Aspirin resistance among long-term aspirin users after carotid endarterectomy and controls: Flow cytometric measurement of aspirin-induced platelet inhibition

BACKGROUND

Numerous studies have indicated that some patient subpopulations do not respond to the antithrombotic effects of aspirin. The objective of this study was to evaluate aspirin-induced inhibition of platelet cyclooxygenase (COX) using a flow cytometric technique in long-term aspirin users after carotid endarterectomy (CEA) and controls with newly diagnosed carotid stenosis not taking aspirin and to compare these results with platelet function analyzer measurements.

METHODS

The study included 86 patients with a history of CEA on long-term aspirin therapy (100 mg daily) and 29 age-matched patients with newly diagnosed carotid artery stenosis not taking aspirin. Platelet-rich plasma diluted with phosphate-buffered saline was incubated with arachidonic acid (ARA) at a final concentration of 80 micromol/L. After staining with phycoerythrin-labeled anti-P-selectin (CD62p) antibody, platelet CD62p-antigen expression was measured on a flow cytometer.

RESULTS

Flow cytometric measurement of ARA-induced platelet activation showed an inhibition of ARA-induced platelet stimulation in all patients on aspirin therapy, whereas all but two controls (95%) showed expected platelet reactivity. In contrast, results of the platelet function analyzer measurements were normal in 16% of aspirin-treated patients.

CONCLUSIONS

Flow cytometric measurement of CD62p expression on platelets after incubation with ARA proved to be a practicable tool to monitor aspirin-induced inhibition of platelet COX. Results in patients on long-term low-dose aspirin therapy show that the inability of aspirin to inhibit platelet COX for both symptomatic and asymptomatic patients with high-grade internal carotid artery stenosis is a very rare event. So-called aspirin resistance detected quite frequently by platelet function analyzer measurement is most likely from COX-independent mechanisms.

Aspirin before reperfusion blunts the infarct size limiting effect of atorvastatin

We assessed whether aspirin (acetylsalicylic acid, ASA), administered before reperfusion, abrogates the infarct size (IS)-limiting effect of atorvastatin (ATV). Statins reduce IS. This dose-dependent effect is mediated by upregulation of cycloxygenase-2 (COX2) and PGI2 production. Administration of selective COX2-inhibitors either with ATV for 3 days or immediately before coronary occlusion blocks the IS-limiting effect of ATV. Sprague-Dawley rats received 3-day ATV (10 mg·kg−1·day−1) or water alone. Rats underwent 30 min coronary artery occlusion and 4 h reperfusion (IS protocol, n = 8 in each group), or rats underwent 30 min coronary artery occlusion and 10 min reperfusion (enzyme expression and activity protocol, n = 4 in each group). Immediately before reperfusion rats received intravenous ASA (5, 10, or 20 mg/kg) or saline. Area-at-risk (AR) was assessed by blue dye and IS by triphenyltetrazolium chloride. ATV reduced IS (10.1 ± 1.4% of the AR) compared with controls (31.0 ± 2.2%). Intravenous ASA alone did not affect IS (29.0 ± 2.6%); however, ASA dose dependently (5, 10, and 20 mg/kg) attenuated the protective effect of ATV on IS (15.8 ± 0.9%, 22.0 ± 1.6%, and 23.7 ± 3.8%, respectively). ASA dose dependently blocked the upregulation of COX2 by ATV. COX2 activity was as follows: control, 8.93 ± 0.90 pg/mg; ATV, 75.85 ± 1.08 pg/mg; ATV + ASA5, 34.39 ± 1.48 pg/mg; ATV + ASA10, 19.87 ± 1.10 pg/mg; and ATV + ASA20, 9.36 ± 0.94 pg/mg. ASA, administered before reperfusion in doses comparable to those used in the clinical setting, abrogates the IS-limiting effect of ATV in a model with mechanical occlusion of the coronary artery. This potential adverse interaction should be further investigated in the clinical setting of acute coronary syndromes.

Aspirin and clopidogrel resistance: consideration and management

The efficacy with aspirin and clopidogrel treatment has been demonstrated in various clinical trials. Laboratory evaluation of platelet response in recent studies revealed that a distinctive response variability and nonresponsiveness/resistance in selected patients were associated with these antiplatelet agents. Moreover, some studies have correlated this nonresponsiveness/resistance phenomenon to the occurrence of thrombotic events. At this time there are no uniformly established methods to quantify exvivo platelet reactivity after clopidogrel and aspirin treatment of the extent of platelet inhibition by clopidogrel and aspirin. Therefore, specific treatment recommendations for patients exhibiting high platelet reactivity or poor platelet inhibition during clopidogrel or aspirin therapy are not established. A higher aspirin dose and strict compliance to therapy may overcome the occurrence of "aspirin resistance" in selected patients. A higher clopidogrel dose may be considered in patients exhibiting clopidogrel nonresponsiveness.

Aspirin and the risk of colorectal cancer in relation to the expression of COX-2

BACKGROUND

Regular use of aspirin reduces the risk of a colorectal neoplasm, but the mechanism by which aspirin affects carcinogenesis in the colon is not well understood.

METHODS

We estimated cyclooxygenase-2 (COX-2) expression by immunohistochemical assay of sections from paraffin-embedded colorectal-cancer specimens from two large cohorts of participants who provided data on aspirin use from a questionnaire every 2 years. We applied Cox regression to a competing-risks analysis to compare the effects of aspirin use on the relative risk of colorectal cancer in relation to the expression of COX-2 in the tumor.

RESULTS

During 2,446,431 person-years of follow-up of 82,911 women and 47,363 men, we found 636 incident colorectal cancers that were accessible for determination of COX-2 expression. Of the tumors, 423 (67%) had moderate or strong COX-2 expression. The effect of aspirin use differed significantly in relation to COX-2 expression (P for heterogeneity=0.02). Regular aspirin use conferred a significant reduction in the risk of colorectal cancers that overexpressed COX-2 (multivariate relative risk, 0.64; 95% confidence interval [CI], 0.52 to 0.78), whereas regular aspirin use had no influence on tumors with weak or absent expression of COX-2 (multivariate relative risk, 0.96; 95% CI, 0.73 to 1.26). The age-standardized incidence rate for cancers that overexpressed COX-2 was 37 per 100,000 person-years among regular aspirin users, as compared with 56 per 100,000 person-years among those who did not use aspirin regularly; in contrast, the rate for cancers with weak or absent COX-2 expression was 27 per 100,000 person-years among regular aspirin users, as compared with 28 per 100,000 person-years among nonregular aspirin users.

CONCLUSIONS

Regular use of aspirin appears to reduce the risk of colorectal cancers that overexpress COX-2 but not the risk of colorectal cancers with weak or absent expression of COX-2.

Heritability of Platelet Responsiveness to Aspirin in Activation Pathways Directly and Indirectly Related to Cyclooxygenase-1

Background— The inability of aspirin (acetylsalicylic acid [ASA]) to adequately suppress platelet function is associated with future risk of myocardial infarction, stroke, and cardiovascular death. Genetic variation is a proposed but unproved mechanism for insufficient ASA responsiveness.

Methods and Results— We examined platelet ASA responsiveness in 1880 asymptomatic subjects (mean age, 44±13 years; 58% women) recruited from 309 white and 208 black families with premature coronary heart disease. Ex vivo platelet function was determined before and after ingestion of ASA (81 mg/d for 2 weeks) with the use of a panel of measures that assessed platelet activation in pathways directly and indirectly related to cyclooxygenase-1, the enzyme inhibited by ASA. The proportion of phenotypic variance related to CHD risk factor covariates was determined by multivariable regression. Heritability of phenotypes was determined with the use of variance components models unadjusted and adjusted for covariates. ASA inhibited arachidonic acid–induced aggregation and thromboxane B 2 production by ≥99% ( P <0.0001). Inhibition of urinary thromboxane excretion and platelet activation in pathways indirectly related to cyclooxygenase-1 was less pronounced and more variable (inhibition of 0% to 100%). Measured covariates contributed modestly to variability in ASA response phenotypes ( r 2 =0.001 to 0.133). Phenotypes indirectly related to cyclooxygenase-1 were strongly and consistently heritable across races (h 2 =0.266 to 0.762; P <0.01), but direct cyclooxygenase-1 phenotypes were not.

Conclusions— Heritable factors contribute prominently to variability in residual platelet function after ASA exposure. These data suggest a genetic basis for the adequacy of platelet suppression by ASA and potentially for differences in the clinical efficacy of ASA.

Cyclooxygenase polymorphisms and risk of cardiovascular events: the Atherosclerosis Risk in Communities (ARIC) study

Cyclooxygenase-derived prostaglandins modulate cardiovascular disease risk. We genotyped 2212 Atherosclerosis Risk in Communities study participants (1,023 incident coronary heart disease (CHD) cases; 270 incident ischemic stroke cases; 919 non-cases) with available DNA for polymorphisms in PTGS1 and PTGS2. Using a case-cohort design, associations between genotype and CHD or stroke risk were evaluated using proportional hazards regression. In Caucasians, the reduced function PTGS1 -1006A variant allele was significantly more common among stroke cases compared to non-cases (18.2 versus 10.6%, P=0.027). In African Americans, the reduced function PTGS2 -765C variant allele was significantly more common in stroke cases (61.4 versus 49.4%, P=0.032). No significant relationships with CHD risk were observed. However, aspirin utilization appeared to modify the relationship between the PTGS2 G-765C polymorphism and CHD risk (interaction P=0.072). These findings suggest that genetic variation in PTGS1 and PTGS2 may be important risk factors for the development of cardiovascular disease events. Confirmation in independent populations is necessary.

Human pharmacology of naproxen sodium

We compared the variability in degree and recovery from steady-state inhibition of cyclooxygenase (COX)-1 and COX-2 ex vivo and in vivo and platelet aggregation by naproxen sodium at 220 versus 440 mg b.i.d. and low-dose aspirin in healthy subjects. Six healthy subjects received consecutively naproxen sodium (220 and 440 mg b.i.d.) and aspirin (100 mg daily) for 6 days, separated by washout periods of 2 weeks. COX-1 and COX-2 inhibition was determined using ex vivo and in vivo indices of enzymatic activity: 1) the measurement of serum thromboxane (TX)B(2) levels and whole-blood lipopolysaccharide-stimulated prostaglandin (PG)E(2) levels, markers of COX-1 in platelets and COX-2 in monocytes, respectively; 2) the measurement of urinary 11-dehydro-TXB(2) and 2,3-dinor-6-keto-PGF(1alpha) levels, markers of systemic TXA(2) biosynthesis (mostly COX-1-derived) and prostacyclin biosynthesis (mostly COX-2-derived), respectively. Arachidonic acid (AA)-induced platelet aggregation was also studied. The maximal inhibition of platelet COX-1 (95.9 +/- 5.1 and 99.2 +/- 0.4%) and AA-induced platelet aggregation (92 +/- 3.5 and 93.7 +/- 1.5%) obtained at 2 h after dosing with naproxen sodium at 220 and 440 mg b.i.d., respectively, was indistinguishable from aspirin, but at 12 and 24 h after dosing, we detected marked variability, which was higher with naproxen sodium at 220 mg than at 440 mg b.i.d. Assessment of the ratio of inhibition of urinary 11-dehydro-TXB(2) versus 2,3-dinor-6-keto-PGF(1alpha) showed that the treatments caused a more profound inhibition of TXA(2) than prostacyclin biosynthesis in vivo throughout dosing interval. In conclusion, neither of the two naproxen doses mimed the persistent and complete inhibition of platelet COX-1 activity obtained by aspirin, but marked heterogeneity was mitigated by the higher dose of the drug.

Nitric oxide-releasing aspirin: Will it say NO to atherothrombosis?

Aspirin is a powerful anti-platelet drug widely used in patients with coronary atherosclerosis, but its side effects and especially its toxicity for gastrointestinal tract limit its usefulness in specific groups of patients. A new category of agents, nitric oxide-releasing aspirins (such as NCX-4016), seems to provide an alternative solution. Although this drug is still at phase II clinical trials, it has provided promising results until now. When administered in vivo, it is separated into an aspirin moiety and an NO-donating complex, providing both the antithrombotic effect of aspirin and the gastroprotective effect of NO. Additionally, it increases NO bioavailability as a vascular level, and it may have the antiatherogenic properties of endogenously produced NO. Finally, recent evidence suggests that it may also improve functional aspects of vein grafts used in CABG, with possible benefit on graft patency. However, the outcome of the large ongoing trials is needed before any conclusion is made about the role of NO-releasing aspirins in cardiovascular disease.

Assessing aspirin-induced attenuation of platelet reactivity by flow cytometry

INTRODUCTION

Certain patient subpopulations do not respond to antithrombotic effects of aspirin and different approaches have been proposed to detect and define this so-called aspirin resistance. In this study, a methodological and clinical evaluation of a flow cytometric method for the detection of aspirin-induced inhibition of platelet cyclooxygenase (COX) is presented.

MATERIALS AND METHODS

Platelet CD62p-antigen (P-selectin) expression was determined by flow cytometry after incubating diluted platelet rich plasma (PRP) with arachidonic acid (ARA). After establishing the method's technical characteristics, it was used to investigate 114 individuals (70 patients with atherosclerotic vascular disease under long-term medication of 100 mg aspirin daily, 29 age-matched patients with vascular disease without anti-platelet medication and 15 healthy volunteers). Data were compared to those obtained by the PFA-100 platelet function analyzer.

RESULTS

Imprecision was between 3.3% and 13%. Sample storage at room temperature increased baseline activity of platelets already after 2 h. After ARA stimulation, the proportion of CD62p-positive platelets was considerably lower in aspirin-treated patients than in controls (median [lower-upper quartile]: 4% [3-6] vs. 50% [29-68], p<0.001). Only one aspirin-treated patient (1.5%) showed normal reactivity to ARA. In contrast to flow cytometry, PFA-100 analysis yielded normal results in 17% of aspirin-treated patients.

CONCLUSIONS

The presented flow cytometric method can be used to monitor aspirin-induced inhibition of platelet COX. Aspirin resistance defined as failure to inhibit platelet COX is a rare phenomenon suggesting that most cases of aspirin resistance detected using the PFA-100 are caused by COX-independent mechanisms.

Flavonoids inhibit the platelet TxA(2) signalling pathway and antagonize TxA(2) receptors (TP) in platelets and smooth muscle cells

AIMS

Flavonoids may affect platelet function by several mechanisms, including antagonism of TxA(2) receptors (TP). These TP are present in many tissues and modulate different signalling cascades. We explored whether flavonoids affect platelet TP signalling, and if they bind to TP expressed in other cell types.

METHODS

Platelets were treated with flavonoids, or other selected inhibitors, and then stimulated with U46619. Similar assays were performed in aspirinized platelets activated with thrombin. Effects on calcium release were analysed by fluorometry and changes in whole protein tyrosine phosphorylation and activation of ERK 1/2 by Western blot analysis. The binding of flavonoids to TP in platelets, human myometrium and TPalpha- and TPbeta-transfected HEK 293T cells was explored using binding assays and the TP antagonist (3)H-SQ29548.

RESULTS

Apigenin, genistein, luteolin and quercetin impaired U46619-induced calcium mobilization in a concentration-dependent manner (IC(50) 10-30 microm). These flavonoids caused a significant impairment of U46619-induced platelet tyrosine phosphorylation and of ERK 1/2 activation. By contrast, in aspirin-treated platelets all these flavonoids, except quercetin, displayed minor effects on thrombin-induced calcium mobilization, ERK 1/2 and total tyrosine phosphorylation. Finally, apigenin, genistein and luteolin inhibited by >50% (3)H-SQ29548 binding to different cell types.

CONCLUSIONS

These data further suggest that flavonoids may inhibit platelet function by binding to TP and by subsequent abrogation of downstream signalling. Binding of these compounds to TP occurs in human myometrium and in TP-transfected HEK 293T cells and suggests that antagonism of TP might mediate the effects of flavonoids in different tissues.

Antiplatelet therapy in type 2 diabetes mellitus

PURPOSE OF REVIEW

Patients with diabetes mellitus are characterized by a prothrombotic status. Since platelet reactivity is key to the development of atherothrombotic complications, antiplatelet therapy has a pivotal role in reducing ischemic risk, especially in diabetes mellitus patients. This review summarizes the current knowledge on how antiplatelet therapy affects this high-risk patient population.

RECENT FINDINGS

Numerous studies have shown the clinical benefit of antiplatelet agents in reducing ischemic events in diabetes mellitus patients. Despite the clinical benefit achieved with antiplatelet agents, however, patients with diabetes mellitus continue to have an increased risk of ischemic events compared to non-diabetes mellitus. Recent observations suggest that this may be in part due to inadequate platelet inhibition achieved in diabetes mellitus patients compared to non-diabetics, exposing these subjects to an enhanced ischemic risk.

SUMMARY

Whilst antiplatelet therapy has been clearly shown to reduce morbidity and mortality in patients with diabetes mellitus, there are accruing data demonstrating that in these patients the degree of platelet inhibition achieved with standard treatment regimens may be inadequate. This supports the need for specific antiplatelet drug regimens, with either different dosages of current medication or development of novel antiplatelet drugs, which are more specific to tackle the hyperreactive diabetic platelet.

[Low-dose aspirin in patients with diabete melitus: risks and benefits regarding macro and microvascular complications]

Aspirin is recommended as cardiovascular disease prevention in patients with diabetes mellitus. Due to the increased risk of bleeding and because of the hypothesis that there could be a worsening of microvascular complications related to aspirin, there has been observed an important underutilization of the drug. However, it is now known that aspirin is not associated with a deleterious effect on diabetic retinopathy and there is evidence indicating that it also does not affect renal function with usual doses (150 mg/d). On the other hand, higher doses may prove necessary, since recent data suggest that diabetic patients present the so called "aspirin resistance". The mechanisms of this resistance are not yet fully understood, being probably related to an abnormal intrinsic platelet activity. The employment of alternative antiplatelet strategies or the administration of higher aspirin doses (150-300 mg/d) should be better evaluated regarding effective cardiovascular disease prevention in diabetes as well as the possible effects on microvascular complications.

Drug-induced immunomodulation to affect the development and progression of atherosclerosis: a new opportunity?

Inflammation and cytokine pathways are crucial for the development and progression of atherosclerotic lesions. In this review, the hypothesis that immunomodulatory drugs provide a possible therapeutic modality for cardiovascular disease is evaluated. Therefore, after a short overview of the specific inflammatory pathways involved in atherosclerosis, literature on the effect of several immunomodulatory drugs, such as nonsteroidal anti-inflammatory drugs, specific cyclooxygenase inhibitors and immunosuppressive drugs, used currently in the prevention of rejection after organ transplant, on the development and progression of atherosclerosis is reviewed. In addition, the pleiotropic immunomodulatory effect of two established cardiovascular drugs (angiotensin-converting enzyme inhibitors and statins) is discussed.

Diseases of aging that emerge from the metabolic syndrome

With advancing age, interpatient variability increases. Physiologic and pathologic apoptosis progress at widely different rates in each organ system in each person. The effect of any disease on an individual depends on the genetic makeup, social and environmental insults, and adequacy of and compliance with medical therapy. Time spent interviewing, examining, and preparing elderly patients preoperatively pays dividends intra- and postoperatively, with fewer "rescue requiring events," fewer "failures to rescue," lower observed-to expected morbidity and mortality ratios, better patient care, and greater patient and professional satisfaction. Elderly patients will require anesthetic services in greater numbers in the years to come. The baby boomers are coming. Are you ready for them?

Therapeutic effects of nitric oxide-aspirin hybrid drugs

This review examines the therapeutic potential and mechanisms of action of drugs known as nitric oxide (NO)-aspirins. Drugs of this class have an NO-releasing moiety joined by ester linkage to the aspirin molecule. NO-aspirins have the capability to release NO in addition to retaining the cyclooxygenase-inhibitory action of aspirin. The protective nature of NO led to the development of NO-aspirins in the hope that they might avoid the gastric side effects associated with aspirin. However, it has become apparent that the drug-derived NO instills potential for a wide range of added beneficial effects over the parent compound. In this review, the authors focus on the analgesic, anti-inflammatory, cardiovascular and chemopreventative actions of compounds of this emerging drug class.

Asymptomatic carotid stenosis: what to do

PURPOSE OF REVIEW

Patients with asymptomatic carotid stenosis are at increased vascular risk but optimal treatment is controversial. We reviewed the current evidence for medical and surgical intervention in these patients.

RECENT FINDINGS

Optimal medical treatment is the most important aspect of management of patients with asymptomatic carotid stenosis. On the basis of previous trials, endarterectomy is only of overall benefit in men, and this benefit may now be obviated by improved medical treatment. There is insufficient evidence to advocate the routine use of carotid angioplasty or stenting in patients with asymptomatic stenosis. Inaccuracy in the measurement of carotid stenosis may contribute to conflicting estimates of stroke risk in relation to the degree of asymptomatic stenosis. Advances in noninvasive imaging of plaque morphology and inflammation and the detection of microembolic signals may help to risk stratify patients but data on clinical usefulness are lacking.

SUMMARY

Absolute benefit from endarterectomy for asymptomatic carotid stenosis is small, but can sometimes be justified in men. Further research is required to determine long-term benefit in women and to risk stratify patients, particularly in the light of advances in medical treatment.

Low-dose aspirin for in vitro fertilization: a systematic review and meta-analysis

Despite recent advances in ovarian stimulation regimens and laboratory techniques, the pregnancy rate of assisted reproduction remains relatively low. New methods that would potentially improve implantation rates are needed. One proposed strategy involves enhancement of blood flow at the implantation site with the use of low-dose aspirin. We conducted a systematic review and meta-analysis to investigate the effect of low-dose aspirin on likelihood of pregnancy in women undergoing in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI). An electronic search of the literature was conducted targeting reports published over the last 26 years. Only randomized controlled trials (RCTs) comparing aspirin with placebo or no treatment in IVF/ICSI women were included in the meta-analysis. A number of relevant outcomes including pregnancy and live birth (LB) rates were investigated. Pooled relative risk (RR) and 95% confidence interval (CI) were calculated using a random-effects model. Inter-study heterogeneity among the trials was assessed using the Cochran's Q test. Ten RCTs were identified from the literature search, six of which met the criteria for inclusion in the meta-analysis. Clinical pregnancy (CP) rate per embryo transfer (ET) was not found to be significantly different between patients who received low-dose aspirin and those who received placebo or no treatment (RR 1.09, 95% CI 0.92-1.29). None of the other outcomes, including CP per cycle, spontaneous abortion or ectopic pregnancy per CP and LB rate per cycle or ET was found to differ significantly between the compared groups. On the basis of up-to-date evidence, low-dose aspirin has no substantial positive effect on likelihood of pregnancy and, therefore, it should not be routinely recommended for women undergoing IVF/ICSI.

The treatment of polycythaemia vera: an update in the JAK2 era

The clinical course of polycythaemia vera is marked by a high incidence of thrombotic complications, which represent the main cause of morbidity and mortality. Major predictors of vascular events are increasing age and previous thrombosis. Myelosuppressive drugs can reduce the rate of thrombosis, but there is concern that their use raises the risk of transformation into acute leukaemia. To tackle this dilemma, a risk-oriented management strategy is recommended. Low-risk patients should be treated with phlebotomy and low-dose aspirin. Cytotoxic therapy is indicated in high-risk patients, with the drug of choice being hydroxyurea because its leukaemogenicity is low. The recent discovery of JAK2 V617F mutation in the vast majority of polycythaemia vera patients opens new avenues for the treatment of this disease. Novel therapeutic options theoretically devoid of leukaemic risk, such as alpha-interferon and imatinib, affect JAK2 expression in some patients. Nevertheless, these drugs require further clinical experience and, for the time being, should be reserved for selected cases.

Determinants of platelet activation in Alzheimer's disease

OBJECTIVES

To investigate the rate of platelet thromboxane (TX) biosynthesis and its determinants in Alzheimer's disease.

METHODS AND RESULTS

A cross-sectional comparison of urinary 11-dehydro-TXB(2) and 8-iso-prostaglandin (PG)F(2alpha) (markers of in vivo platelet activation and lipid peroxidation, respectively), plasma Vitamin E, C-reactive protein (CRP), tumor necrosis factor (TNF)-alpha and interleukin (IL)-6, was carried-out in 44 Alzheimer patients and 44 matched controls. To investigate the cyclooxygenase (COX)-isoform involved in TXA(2) biosynthesis, nine Alzheimer patients were treated with low-dose aspirin (100mg/d) or rofecoxib (25mg/d) for 4 days. Urinary 11-dehydro-TXB(2) and 8-iso-PGF(2alpha) were significantly higher in Alzheimer patients than in controls (Median: 1983.5 versus 517.5pg/mg creatinine and 938.5 versus 304.0pg/mg creatinine, p<0.0001, respectively), with a significant correlation between the two metabolites (rho=0.75, p<0.0001). An inverse correlation was observed between Vitamin E and both urinary metabolites (8-iso-PGF(2alpha): R(s)=-0.51, p=0.0004; 11-dehydro-TXB(2): R(s)=-0.44, p=0.0026) in Alzheimer patients. No difference was found in CRP, TNF-alpha and IL-6 levels between the two groups. Urinary 11-dehydro-TXB(2) was significantly reduced by aspirin, but not by rofecoxib, consistently with a COX-1-mediated TXA(2) biosynthesis. 8-iso-PGF(2alpha) excretion was not modified by either COX-inhibitor, consistently with its oxygen radical-catalyzed formation.

CONCLUSIONS

Platelet activation is persistently enhanced in Alzheimer's disease. This is related, at least in part, to increased lipid peroxidation associated with inadequate levels of Vitamin E.

Platelet-neutrophil-interactions: Linking hemostasis and inflammation

Platelets are essential for primary hemostasis, but they also play an important pro-inflammatory role. Platelets normally circulate in a quiescent state. Upon activation, platelets can secrete and present various molecules, change their shape as well as the expression pattern of adhesion molecules. These changes are associated with the adhesion of platelets to leukocytes and the vessel wall. The interaction of platelets with neutrophils promotes the recruitment of neutrophils into inflammatory tissue and thus participates in host defense. This interaction of neutrophils with platelets is mainly mediated through P-selectin and beta(2) and beta(3) integrins (CD11b/CD18, CD41/CD61). Platelets can also interact with endothelial cells and monocytes. Adherent platelets promote the 'secondary capture' of neutrophils and other leukocytes. In addition, platelets secrete neutrophil and endothelial activators inducing production of inflammatory cytokines. Thus, platelets are important amplifiers of acute inflammation.

Pharmacotherapy Before and After Revascularization: Anticoagulation, Antiplatelet Agents, and Statins

Proper medical management may enhance perioperative and long-term outcomes for patients with peripheral arterial disease (PAD). For patients with PAD, aspirin and statin drugs remain the mainstay of medical management, based on results from multiple randomized clinical trials that have demonstrated improvements in long-term survival and a decrease in cardiovascular events with these agents. There may additional, unintended positive consequences of treatment with statin drugs, including potential improvements in symptoms of claudication and enhanced graft patency after infrainguinal bypass. For patients undergoing surgical or endovascular revascularization, aspirin remains the standard of care for antithrombotic therapy. Beyond this, use of warfarin should be reserved for patients with high-risk surgical bypass grafts to prolong graft patency, because it carries a significant risk of bleeding complications. The utility of clopidogrel after surgical and endovascular infrainguinal revascularization remains undefined but warrants additional study. At this time the only clear indication for clopidogrel in patients with infrainguinal arterial occlusive disease is for PAD patients who are intolerant of aspirin or have a history of coronary artery stenting within the past 6 months. Proper adjunctive pharmacotherapy for the patient with PAD has the potential to improve symptoms, graft patency, and survival in this challenging subset of patients.

Prevalence of persistent platelet reactivity despite use of aspirin: a systematic review

BACKGROUND

The absolute risk of recurrences among patients using aspirin for prevention of cardiovascular events remains high. Persistent platelet reactivity despite aspirin therapy might explain this in part. Reported prevalences of this so-called aspirin resistance vary widely, between 0% and 57%.

OBJECTIVES

The aim of the study was to systematically review all available evidence on prevalence of aspirin resistance and to study determinants of reported prevalence.

METHODS

Using a predefined search strategy, we searched electronic databases MEDLINE, EMBASE, CENTRAL, and Web of Science. To be included in our analysis, articles had to contain a laboratory definition of aspirin resistance, use aspirin as secondary prevention, and report associated prevalence.

RESULTS

We included 34 full-text articles and 8 meeting abstracts. The mean prevalence of aspirin resistance was 24% (95% CI 20%-28%). After adjustment for differences in definition, used dosage, and population, a statistically significant higher prevalence was found in studies with aspirin dosage < or =100 mg compared with > or =300 mg (36% [95% CI 28%-43%] vs 19% [95% CI 11%-26%], P < .0001). Studies measuring platelet aggregation using light aggregometry with arachidonic acid as an agonist had a pooled unadjusted prevalence of 6% (95% CI 0%-12%). In studies using point-of-care platelet function-analyzing devices, the unadjusted prevalence was significantly higher, at 26% (95% CI 21%-31%).

CONCLUSIONS

Prevalences widely differ between studies reporting on aspirin resistance. Both aspirin dosage and the method of defining aspirin resistance strongly influence estimated prevalence, which explains found heterogeneity among studies. On average, it appears that about 1 in 4 individuals may express biochemically defined aspirin resistance.

Complete reversal of acid-induced acute lung injury by blocking of platelet-neutrophil aggregation

Acute lung injury (ALI) causes high mortality, but its molecular mechanisms are poorly understood. Acid aspiration is a frequent cause of ALI, leading to neutrophil sequestration, increased permeability, and deterioration of gas exchange. We investigated the role of platelet-neutrophil interactions in a murine model of acid-induced ALI. Acid aspiration induced P-selectin-dependent platelet-neutrophil interactions in blood and in lung capillaries. Reducing circulating platelets or blocking P-selectin halted the development of ALI. Bone marrow chimeras showed that platelet, not endothelial, P-selectin was responsible for the injury. The interaction of platelets with neutrophils and endothelia was associated with TXA(2) formation, with detrimental effects on permeability and tissue function. Activated platelets induced endothelial expression of ICAM-1 and increased neutrophil adhesion. Inhibition of platelet-neutrophil aggregation improved gas exchange, reduced neutrophil recruitment and permeability, and prolonged survival. The key findings were confirmed in a sepsis-induced model of ALI. These findings may translate into improved clinical treatments for ALI.

Drug insight: aspirin resistance--fact or fashion?

The term aspirin resistance has been used increasingly in clinical studies. The aim of this Review is to analyze the origin of this term, to discuss the biochemical, functional and clinical correlates of the phenomenon and to offer a conceptual framework to redefine the major determinants of variability between individuals in response to aspirin. Awareness needs to be increased of factors that might interfere with the desired antiplatelet effect of aspirin, particularly in terms of patients' adherence to treatment and avoidable drug interactions with some traditional NSAIDs. Gaining such knowledge could result in improved care of patients and might avoid the requesting of unnecessary platelet function tests of unproven clinical significance.

Activation of platelet function through G protein-coupled receptors

Because of their ability to become rapidly activated at places of vascular injury, platelets are important players in primary hemostasis as well as in arterial thrombosis. In addition, they are also involved in chronic pathological processes including the atherosclerotic remodeling of the vascular system. Although primary adhesion of platelets to the vessel wall is largely independent of G protein-mediated signaling, the subsequent recruitment of additional platelets into a growing platelet thrombus requires mediators such as ADP, thromboxane A(2), or thrombin, which act through G protein-coupled receptors. Platelet activation via G protein-coupled receptors involves 3 major G protein-mediated signaling pathways that are initiated by the activation of the G proteins G(q), G(13), and G(i). This review summarizes recent progress in understanding the mechanisms underlying platelet activation and thrombus extension via G protein-mediated signaling pathways.

Essential polyunsaturated fatty acids, inflammation, atherosclerosis and cardiovascular diseases

Atherosclerosis is the primary cause of coronary and cardiovascular diseases (CVD). Epidemiological studies have revealed several important environmental (especially nutritional) factors associated with atherosclerosis. However, progress in defining the cellular and molecular interactions involved has been hindered by the etiological complexity of the disease. Nevertheless, our understanding of CVD has improved significantly over the past decade owing to the availability of new randomized trial data. In particular, the failure of antioxidant and anti-inflammatory treatments to consistently reduce the rate of CVD complications suggests that theories of atherosclerosis may have considerably exaggerated the importance of oxidized lipoprotein and vascular inflammation. In that context, one new and basic question is whether the biology of essential dietary lipids may help us understand the role of the inflammatory process in CVD. Essential dietary lipids of the omega-6 and omega-3 families are the precursors of major mediators of inflammation such as eicosanoids that regulate the production of inflammatory cytokines and the expression of some major inflammation genes. On the other hand, non-essential lipids (omega-9 and saturated fatty acids) interfere with biological activities of essential lipids. Finally, essential omega-3 and omega-6 fatty acids have different, often antagonistic, effects on inflammation, and their effects can vary according to the type of cells and target organs involved, as well as their respective amounts in the diet. Because of the extreme complexity in the etiology of CVD, the best strategy may be to monitor the main features of dietary patterns, such as the Mediterranean diet, that are known to be associated with a low prevalence of both CVD and chronic inflammatory diseases.

From pathophysiology to targeted therapy for atherothrombosis: A role for the combination of statin and aspirin in secondary prevention

Atherothrombosis results from direct interaction between the atherosclerotic plaque and arterial thrombosis, and underlies most forms of cardiovascular disease (CVD). The pathophysiology of atherosclerosis is now recognised to involve endothelial dysfunction and dyslipidemia with cholesterol accumulation, as well as critical immuno-inflammatory and apoptotic dimensions. Erosion or rupture of a vulnerable, lipid-rich, inflammatory atherosclerotic plaque triggers the formation of a platelet-rich thrombus that may partially or completely occlude the artery, with resultant clinical scenarios including stable and unstable angina, acute myocardial infarction (MI) and ischaemic stroke. Insight into the pathophysiology of atherothrombosis indicates that an integrated risk factor approach, focusing particularly on management of dyslipidaemia (with a statin) and thrombosis (with aspirin), may constitute an optimal therapeutic approach. Both agents have established roles in secondary prevention. Statin action on atherogenic lipoproteins mediates plaque stabilisation, modification of plaque morphology and attenuation of inflammation, and may lead to plaque regression, while aspirin reduces platelet activation and aggregation, decreases release of inflammatory cytokines at sites of vascular injury and attenuates vasoconstriction. Given these complementary modes of action, this combination would be a logical choice for reducing atherothrombotic risk in patients with CVD. Meta-analysis of 5 major clinical studies has demonstrated that the combination of pravastatin plus aspirin was significantly more effective than either agent alone in reducing the relative risk of key cardiovascular endpoints including MI and ischaemic stroke. This combination may therefore represent an important, cost-efficient therapeutic approach to reduction of cardiovascular risk and prevention of recurrent events in stable CVD.

A review of aspirin resistance; definition, possible mechanisms, detection with platelet function tests, and its clinical outcomes

Aspirin (acetylsalicylic acid) is one of the main therapeutics in prevention of thrombo-embolic vascular events. Its efficiency is proved in the prevention of cardiovascular events. However, antiplatelet effect of aspirin is not absolute in all patients and some patients experience thrombo-embolic events despite aspirin. These patients are clinically called as aspirin resistant or aspirin non-responders. Globally, a lot of people are affected by aspirin resistance according to the high prevalence of athero-thrombotic vascular diseases. A prevalence of 5.5-45% in patients with various cardiovascular disease by different laboratory methods has been reported for aspirin resistance. Clinical outcome of aspirin resistance has been demonstrated in patients with different vascular diseases. Detection of platelet function in patients treated with aspirin may be necessary in the prediction of clinical outcome. Point of care methods, which have correlated results with the standard light transmittance aggregometry may be appropriate choices in the detection of platelets' response to antiplatelet therapy. Adequate additional therapies may reduce atherothrombotic risks and major cardiovascular events rate in aspirin resistant subjects. None of the current researches advised the cessation of aspirin therapy. There is need to investigate the efficacy of additional adenosine diphosphate receptor antagonists or newer antiplatelet agents in aspirin resistant subjects. The intent of this paper is to review the literature discussing possible mechanisms, determination techniques, and clinical effects of aspirin resistance.

The PGH-synthase system and isozyme-selective inhibition

Virtually all human cell types can express both cyclooxygenase (COX)-1 and COX-2 under appropriate circumstances. Both isoforms can subserve physiologic and pathophysiologic roles when coupled with the appropriate stimuli and downstream prostaglandin (PG)H2-isomerases and prostanoid receptors. Although the ratio of maximal biosynthetic capacity of human platelets to the basal rate of production of thromboxane A2 is approximately 5000, this ratio is much lower in the case of PGI2, thus dictating quite different requirements for the extent and duration of COX inhibition in human platelets and vascular endothelial cells to detect functional and clinical effects. The development of low-dose aspirin as an antiplatelet agent has been instrumental in characterizing the role of platelet COX-1 in atherothrombosis. Similarly, though quite unexpectedly, the development of coxibs as anti-inflammatory agents has been instrumental in elucidating the role of endothelial COX-2 in vascular occlusion. Because of differential requirements for the inhibition of thromboxane A2 versus PGI2 biosynthesis in vivo, most traditional nonsteroidal anti-inflammatory drugs tend to mimic the effects of coxibs, rather than aspirin, on prostanoid-dependent cardiovascular homeostasis.

Aspirin augments 15-epi-lipoxin A4 production by lipopolysaccharide, but blocks the pioglitazone and atorvastatin induction of 15-epi-lipoxin A4 in the rat heart

Aspirin (ASA) inhibits cycloxygenase-1 and modifies cycloxygenase-2 (COX2) by acetylation at Ser(530), leading to a shift from production of PGH(2), the precursor of prostaglandin, to 15-R-HETE which is converted by 5-lipoxygenase to 15-epi-lipoxin A(4) (15-epi-LXA4), a potent anti-inflammatory mediator. Both atorvastatin (ATV) and pioglitazone (PIO) increase COX2 expression. ATV activates COX2 by S-nitrosylation at Cys(526) to produce 15-epi-LXA4 and 6-keto-PGF(1alpha) (the stable metabolite of PGI(2)). We assessed the effect of ASA on the myocardial production of 15-epi-LXA4 and PGI(2) after induction by lipopolysaccharide (LPS) or PIO+ATV. Sprague-Dawley rats were pretreated with: control; ASA 10 mg/kg; ASA 50 mg/kg; LPS alone; LPS+ASA 10 mg/kg; LPS+ASA 50 mg/kg; LPS+ASA 200 mg/kg; PIO (10 mg/kg/d)+ATV (10 mg/kg/d); PIO+ATV+ASA 10 mg/kg; PIO+ATV+ASA 50 mg/kg; PIO+ATV+ASA 50 mg/kg+1400 W, a specific iNOS inhibitor; or PIO+ATV+1400 W. ASA alone had no effect on myocardial 15-epi-LXA4. LPS increased 15-epi-LXA4 and 6-keto-PGF(1alpha) levels. ASA (50 mg/kg and 200 mg/kg, but not 10 mg/kg) augmented the LPS effect on 15-epi-LXA4 but attenuated the effect on 6-keto-PGF(1alpha). PIO+ATV increased 15-epi-LXA4 and 6-keto-PGF(1alpha) levels. ASA and 1400 W attenuated the effects of PIO+ATV on 15-epi-LXA4 and 6-keto-PGF(1alpha). However, when both ASA and 1400 W were administered with PIO+ATV, there was a marked increase in 15-epi-LXA4, whereas the production of 6-keto-PGF(1alpha) was attenuated. In conclusion, COX2 acetylation by ASA shifts enzyme from producing 6-keto-PGF(1alpha) to 15-epi-LXA4. In contrast, S-nitrosylation by PIO+ASA augments the production of both 15-epi-LXA4 and 6-keto-PGF(1alpha). However, when COX2 is both acetylated and S-nitrosylated, it is inactivated. We suggest potential adverse interactions among statins, thiazolidinediones, and high-dose ASA.

The benefit of aspirin chemoprophylaxis for thromboembolism after total knee arthroplasty

The threat of thromboembolic events after total knee arthroplasty has been substantially reduced during the past decade. Currently, the risk of fatal pulmonary embolism is approximately 0.1%. This is due to a confluence of changes in our medical practices, including early mobilization, less traumatic surgery, increased use of regional anesthesia, pneumatic compression devices, and chemoprophylactic agents. Because many chemoprophylactic agents are associated with an increased risk of bleeding, we have chosen aspirin as our preferred method of chemoprophylaxis. This study seeks to determine if aspirin is as effective as newer chemoprophylactic agents as judged by the prevalence of fatal or nonfatal pulmonary embolus, readmission for deep venous thrombosis, and risk of bleeding. Aspirin was the principle chemoprophylactic agent for 3473 consecutive patients having total knee arthroplasty. All patients were followed for a minimum of 6 weeks. There were nine deaths: two from pulmonary embolism, five cardiac events, one stroke, and one fat embolism. Three cardiac-related deaths occurred in patients for whom pulmonary embolism could not definitively be ruled out. Therefore, the best case and worst case scenarios for fatal pulmonary embolism were 0.06% and 0.14%, respectively. Thirteen patients underwent reoperation for hematoma (0.4%). Therefore, we have demonstrated aspirin combined with early mobilization, regional anesthesia, foot pumps, and improved surgical techniques is safer than and equally efficacious as other chemoprophylaxis agents.

Impact of adherence to concomitant gastroprotective therapy on nonsteroidal-related gastroduodenal ulcer complications

BACKGROUND & AIMS

The clinical impact of nonadherence to gastroprotective agents (GPAs) coprescribed with anti-inflammatory therapies has not been evaluated. In a large, commercial, managed-care database, we retrospectively characterized the use of GPAs among patients receiving nonselective nonsteroidal anti-inflammatory drugs (ns-NSAIDs) or cyclooxygenase-2-selective inhibitors (coxibs) and determined the impact of nonadherence on the likelihood of gastroduodenal ulcer complications.

METHODS

Analyses identified the populations of patients with concomitant histamine-2 receptor antagonist or proton pump inhibitor (PPI) therapy and determined adherence with the prescribed therapy with respect to the duration of anti-inflammatory treatment. Multivariate regression analyses modeled the association between adherence with concomitant protective therapy and the likelihood of upper gastrointestinal (GI) complications including peptic ulcer disease, ulcer, and/or upper-GI bleed.

RESULTS

Among 144,203 patients newly prescribed anti-inflammatory therapies, 1.8% received concomitant GPA treatment (ns-NSAIDs, 1.4% vs coxibs, 2.6%; P < .0001). The likelihood of GPA use increased with the presence of risk factors: age older than 65 years (odds ratio [OR], 1.40; 95% confidence interval [CI], 1.3-1.5) and prior history of peptic ulcer disease (OR, 2.5; 95% CI, 1.8-3.3), esophagitis/gastroesophageal reflux (OR, 3.8; 95% CI, 3.5-4.1), ulcer/upper-GI bleed (OR, 1.4; 95% CI, 1.2-1.5), or gastritis (OR, 2.5; 95% CI, 2.2-2.8). Of patients receiving concomitant PPI therapy, 68% had adherence rates of 80% or more. A significantly higher risk of upper-GI ulcers/complications was observed in ns-NSAID patients with adherence rates of less than 80% compared with adherence rates of 80% or more (OR, 2.4; 95% CI, 1.0-5.6), but no such relationship was observed among patients who took coxibs.

CONCLUSIONS

Few patients receive concomitant GPA therapy when prescribed anti-inflammatory treatment, although use increased with the presence of risk factors. Adherence to concomitant therapy is paramount to reducing GI events among ns-NSAID users and educational efforts should be undertaken to promote use of and adherence to GPA therapy among these patients.

Use of single and combined antithrombotic therapy and risk of serious upper gastrointestinal bleeding: population based case-control study

OBJECTIVES

To assess the risk of serious upper gastrointestinal bleeding associated with the newer antithrombotic agents used alone or in combination with other antithrombotic drugs; to describe the trends in use of antithrombotic drugs in the background population.

DESIGN

Population based case-control study.

SETTING

Funen County, Denmark (population 470,000).

SUBJECTS

1443 cases of serious upper gastrointestinal bleeding identified during 2000-4; 57,720 age and sex matched controls.

MAIN OUTCOME MEASURE

Exposure to low dose aspirin, clopidogrel, dipyridamole, vitamin K antagonists, and combined antithrombotic treatment.

RESULTS

Adjusted odds ratios associating drug use with upper gastrointestinal bleeding were 1.8 (95% confidence interval 1.5 to 2.1) for low dose aspirin, 1.1 (0.6 to 2.1) for clopidogrel, 1.9 (1.3 to 2.8) for dipyridamole, and 1.8 (1.3 to 2.4) for vitamin K antagonists. Corresponding figures for combined use were 7.4 (3.5 to 15) for clopidogrel and aspirin, 5.3 (2.9 to 9.5) for vitamin K antagonists and aspirin, and 2.3 (1.7 to 3.3) for dipyridamole and aspirin. Other combinations were used too infrequently to allow estimation. The number of treatment years needed to produce one excess case varied from 124 for the clopidogrel-aspirin combination to 8800 for clopidogrel alone. During the study period, exposure to combined antithrombotic regimens increased by 425% in the background population.

CONCLUSION

Antithrombotic treatment is becoming increasingly aggressive. Combined antithrombotic treatment confers particular risk and is associated with high incidence of gastrointestinal bleeding.

Possible mechanisms of drug-induced aspirin and clopidogrel resistance

Aspirin (ASA) and clopidogrel have been identified as standard of care in the prevention of major cardiovascular events. Aspirin irreversibly inhibits the cyclooxygenase-1 (COX-1) enzyme, whereas non-steroidal anti-inflammatory drugs (NSAIDs) reversibly inhibit the COX-1 enzyme. An analysis of the literature revealed a statistically significant decrease in clinical benefit of ASA with concomitant administration of ibuprofen. Another NSAID, diclofenac, showed minimal effect on the inhibition of platelet aggregation when administered with ASA. Furthermore, the selective COX-2 inhibitor, rofecoxib, was not shown to influence the effect of ASA. Clopidogrel is metabolized to an active thiol metabolite by the CYP 3A4 enzyme. Some HMG CoA reductase inhibitors have the ability to inhibit the CYP 3A4 enzyme, which can result in a possible interaction if administered concomitantly with clopidogrel. Studies have demonstrated clopidogrel's platelet inhibition being significantly attenuated by atorvastatin. However in a post-hoc analysis, it was demonstrated that there was no difference in clinical outcomes between patients taking clopidogrel and HMG-CoA reductase inhibitors metabolized by and not metabolized by CYP 3A4. Data suggest that the interaction observed involving clopidogrel and HMG-CoA reductase inhibitors appears to be significant in-vitro. Therefore, practitioners should advise patients receiving chronic aspirin therapy to limit the use of ibuprofen and may consider concomitant administration of clopidogrel with HMG-CoA reductase inhibitors without regard for the drug interaction. The intent of this paper is to review the literature discussing possible mechanisms of drug-induced aspirin and clopidogrel resistance and discuss whether the interactions translate into clinical effects.

Cardioprotective aspirin users and their excess risk of upper gastrointestinal complications

BACKGROUND

To balance the cardiovascular benefits from low-dose aspirin against the gastrointestinal harm caused, studies have considered the coronary heart disease risk for each individual but not their gastrointestinal risk profile. We characterized the gastrointestinal risk profile of low-dose aspirin users in real clinical practice, and estimated the excess risk of upper gastrointestinal complications attributable to aspirin among patients with different gastrointestinal risk profiles.

METHODS

To characterize aspirin users in terms of major gastrointestinal risk factors (i.e., advanced age, male sex, prior ulcer history and use of non-steroidal anti-inflammatory drugs), we used The General Practice Research Database in the United Kingdom and the Base de Datos para la Investigación Farmacoepidemiológica en Atención Primaria in Spain. To estimate the baseline risk of upper gastrointestinal complications according to major gastrointestinal risk factors and the excess risk attributable to aspirin within levels of these factors, we used previously published meta-analyses on both absolute and relative risks of upper gastrointestinal complications.

RESULTS

Over 60% of aspirin users are above 60 years of age, 4 to 6% have a recent history of peptic ulcers and over 13% use other non-steroidal anti-inflammatory drugs. The estimated average excess risk of upper gastrointestinal complications attributable to aspirin is around 5 extra cases per 1,000 aspirin users per year. However, the excess risk varies in parallel to the underlying gastrointestinal risk and might be above 10 extra cases per 1,000 person-years in over 10% of aspirin users.

CONCLUSION

In addition to the cardiovascular risk, the underlying gastrointestinal risk factors have to be considered when balancing harms and benefits of aspirin use for an individual patient. The gastrointestinal harms may offset the cardiovascular benefits in certain groups of patients where the gastrointestinal risk is high and the cardiovascular risk is low.

Review article: gastrointestinal bleeding with low-dose aspirin - what's the risk?

This review examines ulcers and gastrointestinal bleeding with low-dose aspirin, focusing on randomized placebo-controlled trials. The single endoscopic trial assessing ulcers showed no significant difference in 12-week ulcer incidence: 6% of 381 given placebo vs. 7% of 387 given 81 mg enteric-coated aspirin. The relative risk of major gastrointestinal bleeding with low-dose aspirin in a meta-analysis of placebo-controlled trials of vascular protection was 2.07 (95% CI: 1.61-2.66). The absolute rate increase with aspirin above placebo was 0.12% per year (95% CI: 0.07-0.19%) with a number-needed-to-harm of 833 patients (95% CI: 526-1429). A meta-analysis of aspirin 50-1500 mg daily reported an odds ratio for any gastrointestinal bleeding of 1.68 (95% CI: 1.51-1.88) with an number-needed-to-harm at 1 year of 247. The relative risk of hospitalization for upper gastrointestinal bleeding with low-dose aspirin in a large Danish cohort study was 2.6 (95% CI: 2.2-2.9) with an absolute annual incidence of 0.6%. Factors that may increase the risk of gastrointestinal bleeding include prior history of ulcers or gastrointestinal bleeding, corticosteroid use, anticoagulant therapy and addition of a non-aspirin non-steroidal anti-inflammatory drug. When determining whether low-dose aspirin is appropriate for an individual patient, the cardiovascular benefit must be weighed against the potential for clinical events such as gastrointestinal bleeding.

Aspirin resistance: is this term meaningful?

PURPOSE OF REVIEW

To review data for and against the existence of 'aspirin resistance', a term coined to indicate aspirin-treated patients having ex-vivo tests of platelet activation insensitive to aspirin treatment and recurrence of cardiovascular disease.

RECENT FINDINGS

'Aspirin resistance' defined by ex-vivo tests of platelet activation yielded values ranging from 21 to 78%, indicating that such tests do not provide a useful measurement. In long-term aspirin-treated patients, studies demonstrated small but functionally relevant platelet thromboxane A2 formation that was responsible for an enhanced platelet activation in response to platelet agonist. These studies, however, did not fully exclude that aspirin compliance may be implicated in such phenomena. Two trials performed in patients with coronary artery disease demonstrated that laboratory evidence of aspirin resistance was no longer detectable when aspirin compliance was accurately monitored.

SUMMARY

Given the multifactorial nature of atherothrombosis, recurrence of cardiovascular events in aspirin-treated patients does not necessarily suggest 'drug failure'. A cause-effect relationship between platelet insensitivity to aspirin and cardiovascular recurrence has not been defined overall because aspirin compliance has been scarcely considered. Until this information is taken into account, the existence of 'clinical resistance' to aspirin should be reconsidered.

Aspirin resistance: truth or dare

Acetylsalicylic acid, or aspirin (ASA), is widely used in patients with cardiovascular disease to prevent acute ischemic events. However, platelet response to ASA is not equal in all individuals, and a high variability in the prevalence of ASA resistance is reported in the literature (0.4-83%). Actually, ASA resistance is poorly understood; this stems from the fact that its definition is unclear, its presence can be evaluated by a number of assays that are not equivalent, and its prevalence may vary widely based on the population studied. This article (1) exposes the difficulties in defining ASA resistance; (2) discusses the mechanisms by which ASA resistance may occur; (3) presents the characteristics that may put patients at greater risk of exhibiting ASA resistance; and (4) discusses the clinical impact of ASA resistance in patients requiring chronic therapy.

Pharmacodynamic of cyclooxygenase inhibitors in humans

We provide comprehensive knowledge on the differential regulation of expression and catalysis of cyclooxygenase (COX)-1 and COX-2 in health and disease which represents an essential requirement to read out the clinical consequences of selective and nonselective inhibition of COX-isozymes in humans. Furthermore, we describe the pharmacodynamic and pharmacokinetic characteristics of major traditional nonsteroidal anti-inflammatory drugs (tNSAIDs) and coxibs (selective COX-2 inhibitors) which play a prime role in their efficacy and toxicity. Important information derived from our pharmacological studies has clarified that nonselective COX inhibitors should be considered the tNSAIDs with a balanced inhibitory effect on both COX-isozymes (exemplified by ibuprofen and naproxen). In contrast, the tNSAIDs meloxicam, nimesulide and diclofenac (which are from 18- to 29-fold more potent towards COX-2 in vitro) and coxibs (i.e. celecoxib, valdecoxib, rofecoxib, etoricoxib and lumiracoxib, which are from 30- to 433-fold more potent towards COX-2 in vitro) should be comprised into the cluster of COX-2 inhibitors. However, the dose and frequency of administration together with individual responses will drive the degree of COX-2 inhibition and selectivity achieved in vivo. The results of clinical pharmacology of COX inhibitors support the concept that the inhibition of platelet COX-1 may translate into an increased incidence of serious upper gastrointestinal bleeding but this effect on platelet COX-1 may mitigate the cardiovascular hazard associated with the profound inhibition of COX-2-dependent prostacyclin (PGI2).