Platelet-active drugs: the relationships among dose, effectiveness, and side effects

[Prevention of gastroduodenal complications in patients taking low-dose aspirin]

Use of low-dose aspirin is associated with an increased risk of gastroduodenal ulcers and upper gastrointestinal bleeding. The risk is increased by the old age and by cardiovascular and cerebrovascular diseases of the patients receiving low-dose aspirin. Combination with nonsteroidal anti-inflammatory drugs, corticosteroids or anticoagulant increases the risk of complications and should be avoided. Proton-pump inhibitor and eradication of Helicobacter pylori are not efficient in primary prevention of ulcer complications related to low-dose aspirin use. Patients at high risk of gastroduodenal complications due to age, morbidity or concomitant use of gastrotoxic therapy should be given prophylactic treatment. Assessment of what constitutes the most effective therapy (misoprostol, proton-pump inhibitor) should be defined in controlled trials. Among patients with Helicobacter pylori infection and a history of upper gastrointestinal bleeding who are taking low-dose aspirin, the eradication of Helicobacter pylori is equivalent to treatment with proton-pump inhibitor in preventing recurrent bleeding. Long term treatment with proton-pump inhibitor in addition to the eradication of Helicobacter pylori should be considered in patients who had ulcer complications related to the use of low-dose aspirin.

Selective COX-2 inhibition and cardiovascular effects: a review of the rofecoxib development program

See related Editorials on pages 561 and 563. Cyclo-oxygenase-2 (COX-2) inhibitors appear to alter the balance of vasoactive eicosanoids (prostacyclin and thromboxane) and to suppress the inflammatory mediators implicated in the progression of atherogenesis and ischemic myocardial injury. Neutral, harmful, and beneficial cardiovascular (CV) effects have all been postulated to result from these changes. Investigations conducted with rofecoxib, a selective COX-2 inhibitor, have substantially contributed to our understanding of this scientific area. Rofecoxib had little or no effect on platelet aggregation or platelet-derived thromboxane synthesis but reduced systemic prostacyclin synthesis by 50% to 60%. These findings prompted extensive analyses of CV thrombotic events within the rofecoxib development program. Among 5435 osteoarthritis trial participants, similar rates of CV thrombotic events were reported with rofecoxib, placebo, and comparator, nonselective NSAIDs (ibuprofen, diclofenac, and nabumetone). In the VIGOR gastrointestinal outcomes trial of >8000 patients, naproxen (an NSAID with aspirin-like sustained antiplatelet effects throughout its dosing interval) was associated with a significantly lower risk of CV events than was rofecoxib. A subsequent pooled analysis from 23 studies (including VIGOR) encompassing multiple disease states and including more than 14,000 patient-years at risk also demonstrated that rofecoxib was not associated with excess CV thrombotic events compared with either placebo or nonnaproxen NSAIDs. Again, naproxen appeared to be the outlier, suggesting a cardioprotective benefit of naproxen. Finally, among the predominantly elderly, male population participating in Alzheimer trials, both rofecoxib- and placebo-treated patients had similar rates of CV thrombotic events. The totality of data is not consistent with an increased CV risk among patients taking rofecoxib.

Effect of different aspirin doses on platelet aggregation in patients with stable coronary artery disease

BACKGROUND

Aspirin is widely used as an antiplatelet agent in the primary and secondary prevention of cardiovascular disease. In order to spare prostacyclin formation and reduce gastrointestinal side-effects, very low doses of aspirin have been introduced. However, it remains unclear whether these low doses are equally effective with respect to inhibition of platelet aggregation.

AIMS

In a randomized, controlled study in 60 patients with stable coronary artery disease, the effects on platelet aggregation of five doses (50, 80, 100, 162.5 and 325 mg) of aspirin, which are widely used in clinical practice, given for 70 days, were investigated. Two reagents, adenosine diphosphate (ADP) and epinephrine, were used to induce platelet aggregation in platelet-rich plasma. An age- and sex-matched group of people without coronary artery disease served as the control.

RESULTS

ADP- and epinephrine-induced platelet aggregation was 78.2 +/- 12.8% and 76.7 +/- 15.5% of maximum aggregation in the control group. Aspirin inhibited platelet aggregation in a dose-dependent manner. Minimum platelet aggregation was observed at a dose of 325 mg aspirin (27.5 +/- 17.4% with ADP). Doses of 50 and 80 mg aspirin were much less effective in inhibiting platelet aggregation (59.1 +/- 11.4% and 50.3 +/- 12.1% with ADP, respectively). Doses of 100 and 162.5 mg aspirin produced significantly greater inhibition of platelet aggregation than lower doses (36.2 +/- 11.7% and 38.5 +/- 19.8% platelet aggregation with ADP, respectively).

CONCLUSION

Our results demonstrate that doses of aspirin less than 100 mg are not as effective at inhibiting platelet aggregation as doses greater than 100 mg.

A benefit-risk assessment of agents used in the secondary prevention of stroke

Stroke is a major cause of morbidity and mortality. Full assessment of stroke or transient ischaemic attack (TIA) patients is required to identify all risk factors and apply appropriate secondary preventative strategies. Antiplatelet therapies are effective in the secondary prevention of ischaemic stroke and can be justified despite adverse effects such as gastrointestinal haemorrhage. Aspirin (acetylsalicylic acid), aspirin plus dipyridamole, ticlopidine and clopidogrel are all of value but their adverse effect profiles vary significantly. Combinations of antiplatelet agents may offer additional benefit but not all combinations have been studied in stroke patients. Anticoagulation with agents such as warfarin is effective with coexisting atrial fibrillation and other conditions predisposing to cardioembolic stroke. Antihypertensive agents have been extensively studied in the primary prevention of stroke; however, relatively few trials of antihypertensive agents in the secondary prevention of stroke are available. The incidence of adverse effects of antihypertensive agents is relatively low and the benefit-risk profile would tend to favour their use in the secondary prevention of stroke. Recent studies of ACE inhibitors have identified an important role for these agents in the secondary prevention of stroke even in those who are normotensive and in those who have had a haemorrhagic stroke. The incidence of serious adverse effects with ACE inhibitors appears relatively low. Lipid-lowering agents may have a role to play in certain groups of patients with stroke. The incidence of adverse effects is relatively low with HMG-CoA reductase inhibitors. Cigarette smoking is an important risk factor for stroke and evidence is available that smoking cessation does reduce the individual's risk of stroke. Pharmacological agents are available to help smoking cessation. In patients with diabetes mellitus, intensive regimens with insulin and oral hypoglycaemic agents have so far not definitively been shown to reduce the incidence of macrovascular complications such as stroke. Tight glycaemic control has been shown to improve microvascular complications such as retinopathy, nephropathy and neuropathy and hence this is reason enough to advocate the use of these agents. Future developments in the treatment of diabetes may help. Secondary prevention of stroke has improved greatly over the past decade and hopefully will continue to improve. The use of pharmacological agents available currently and in the future will be clarified and refined as further clinical trials report.

Antiplatelet therapy for acute ischaemic stroke

BACKGROUND

In patients with acute ischaemic stroke, platelets become activated. Antiplatelet therapy might reduce the volume of brain damaged by ischaemia and reduce the risk of early recurrent ischaemic stroke. This might reduce the risk of early death and improve long-term outcome in survivors. However, antiplatelet therapy might also increase the risk of fatal or disabling intracranial haemorrhage.

OBJECTIVES

The aim of this review is to assess the efficacy and safety of antiplatelet therapy in acute ischaemic stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched August 2002), the Cochrane Controlled Trials Register (CCTR) (Cochrane Library Issue 1 2002), MEDLINE (June 1998-October 2001), and EMBASE (June 1998-February 2002). In 1998, for previous versions of this review, we searched the register of the Antiplatelet Trialists Collaboration, MedStrategy and contacted relevant drug companies.

SELECTION CRITERIA

Randomised trials comparing antiplatelet therapy (started within 14 days of the stroke) with control in patients with definite or presumed ischaemic stroke.

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied the inclusion criteria and assessed trial quality, and for the included trials, extracted and cross-checked the data.

MAIN RESULTS

Nine trials involving 41,399 patients were included. Two trials testing aspirin 160 to 300 mg once daily started within 48 hours of onset contributed 98% of the data. The maximum follow-up was six months. With treatment, there was a significant decrease in death or dependency at the end of follow-up (OR = 0.94; 95% CI 0.91 to 0.98). In absolute terms, 13 more patients were alive and independent at the end of follow-up for every 1000 patients treated. Furthermore, treatment increased the odds of making a complete recovery from the stroke (OR = 1.06; 95% CI 1.01 to 1.11). In absolute terms, 10 more patients made a complete recovery for every 1000 patients treated. Antiplatelet therapy was associated with a small but definite excess of 2 symptomatic intracranial haemorrhages for every 1000 patients treated, but this was more than offset by a reduction of 7 recurrent ischaemic strokes and about one pulmonary embolus for every 1000 patients treated.

REVIEWER'S CONCLUSIONS

Antiplatelet therapy with aspirin 160 to 300 mg daily, given orally (or per rectum in patients who cannot swallow), and started within 48 hours of onset of presumed ischaemic stroke reduces the risk of early recurrent ischaemic stroke without a major risk of early haemorrhagic complications and improves long-term outcome.

[What is the place of aspirin in venous thrombosis prophylaxis?]

Since Virchow triade, it is well established that venous thrombosis is a multifactorial process involving various cellular and plasmatic protagonists. Aspirin antihrombotic efficacy seems not only due to its antiplatelet effects and thromboxane A2 synthesis inhibition. Anti-Platelet Trialists Collaboration metaanalysis stressed in 1994 the interest of aspirin treatment leading to 40% reduction of thrombosis relative risk. Regarding studies heterogeneity and outcomes criteria variety, its use in such context remains a matter of debate. Is the recent publication of PEP trial showing a significant decrease of pulmonary embolism mortality (0.6 versus 0.3%, p = 0.03) able to reinforce aspirin use in venous thrombosis prophylaxis? Were numerous and consecutive criticisms justified? Is there still a potential indication for aspirin in this setting? The experts of the last ACCP consensus conference recommended not to recommend aspirin in venous thrombosis prophylaxis with the highest level of evidence (grade A).

Treatment and monitoring of patients with antiphospholipid antibodies and thrombotic history (Hughes syndrome)

Patients with Hughes (antiphospholipid) syndrome who develop an initial thrombosis have an increased risk of subsequent thrombotic events. Current therapy to prevent recurrent thrombosis is controversial. While it seems clear that anticoagulant treatment is a better option than anti-aggregants alone, there is no consensus regarding the duration and intensity of oral anticoagulation. The risk of bleeding, the main complication of anticoagulant treatment, and the need for frequent monitoring of the International Normalized Ratio to measure the anticoagulant effect of warfarin concern patients and physicians. In addition, there is some debate about the validity of the International Normalized Ratio in patients with lupus anticoagulant activity. The development of new therapies that target more specific pathogenic mechanisms is highly warranted.

Oral single high-dose aspirin results in a long-lived inhibition of anodal current-induced vasodilatation

1 Acetyl salicyclic acid (aspirin) irreversibly blocks cyclo-oxygenase (COX). This effect is short-lived in endothelial or smooth muscle cells due to resynthesis but long-lived in platelets devoid of synthesis ability. Aspirin blocks the anodal current-induced vasodilatation, suggesting participation by prostaglandin (PG). We analysed the time course of the effect of aspirin as an indirect indicator of the origin of the PG possibly involved in anodal current-induced vasodilatation. 2 In healthy volunteers, vasodilatation, estimated from the peak cutaneous vascular conductance (CVC(peak)), was recorded in the forearm during and in the 20 min following 5 min, 0.10 mA transcutaneous anodal current application, using deionized water as a vehicle. CVC(peak) was normalized to 44 degrees C heat-induced maximal vasodilatation and expressed in per cent values. Experiments were performed before and at 2 and 10 h, 3, 7, 10 and 14 days after blinded 1-g aspirin or placebo treatment. 3 CVC(peak) (mean+/-s.d.mean) after aspirin vs placebo was 13.6+/-14.5 vs 65.0+/-32.1 (P<0.05) 14.7+/-4.2 vs 87.5+/-31.9 (P<0.05), 18.1+/-10.2 vs 71.6+/-26.8 (P<0.05), 42.5+/-23.4 vs 73.3+/-26.8 (non significant, NS), 60.2+/-24.3 vs 75.2+/-26.9 (NS), 52.1+/-18.5 vs 67.9+/-32.1 (NS) at 2 and 10 h and at days 3, 7, 10 and 14 respectively. 4 Aspirin inhibition of anodal current-induced vasodilatation persists long after endothelial and smooth muscle cyclo-oxygenases are assumed to be restored. This suggests that the PG involved in this response are not endothelial- or smooth muscle-derived. The underlying mechanism of this unexpected long-lived inhibition of vasodilatation by single high dose aspirin remains to be studied.

Antithrombotic Secondary Prevention After Stroke

In patients with transient ischemic attack (TIA) or ischemic stroke of noncardiac origin, antiplatelet drugs are able to decrease the risk of stroke by 11% to 15%, and decrease the risk of stroke, myocardial infarction (MI), and vascular death by 15% to 22%. Aspirin leads to a moderate but significant reduction of stroke, MI, and vascular death in patients with TIA and ischemic stroke. Low doses are as effective as high doses, but are better tolerated in terms of gastrointestinal side effects. The recommended aspirin dose, therefore, is between 50 and 325 mg. Bleeding complications are not dose-dependent, and also occur with the lowest doses. The combination of aspirin (25 mg twice daily) with slow-release dipyridamole (200 mg twice daily) is superior compared with aspirin alone for stroke prevention. Ticlopidine is effective in secondary stroke prevention in patients with TIA and stroke. For some end points, it is superior to aspirin. Due to its side-effect profile (neutropenia, thrombotic thrombocytopenic purpura ), ticlopidine should be given to patients who are intolerant of aspirin. Prospective trials have not indicated whether ticlopidine is suggested for patients who have recurrent cerebrovascular events while on aspirin. Clopidogrel has a better safety profile than ticlopidine. Although not investigated in patients with TIA, clopidogrel should also be effective in these patients assuming the same pathophysiology than in patients with stroke. Clopidogrel is second-line treatment in patients intolerant for aspirin, and first-line treatment for patients with stroke and peripheral arterial disease or MI. A frequent clinical problem is patients who are already on aspirin because of coronary heart disease or a prior cerebral ischemic event, and then suffer a first or recurrent TIA or stroke. No single clinical trial has investigated this problem. Therefore, recommendations are not evidence-based. Possible strategies include the following: continue aspirin, add dipyridamole, add clopidogrel, switch to ticlopidine or clopidogrel, or switch to anticoagulation with an International Normalized Ratio (INR) of 2.0 to 3.0. The combination of low-dose warfarin and aspirin was never studied in the secondary prevention of stroke. In patients with a cardiac source of embolism, anticoagulation is recommended with an INR of 2.0 to 3.0. At the present time, anticoagulation with an INR between 3.0 and 4.5 cannot be recommended for patients with noncardiac TIA or stroke. Anticoagulation with an INR between 3.0 and 4.5 carries a high bleeding risk. Whether anticoagulation with lower INR is safe and effective is not yet known. Treatment of vascular risk factors should also be performed in secondary stroke prevention.

The role of low-molecular-weight heparin in cardiovascular diseases

Unfractionated heparin continues to have important limitations in clinical practice. It has an inconsistent anticoagulant effect, needs frequent monitoring, and is inactivated by several plasma proteins. Low-molecular-weight heparins have a more predictable anticoagulant effect than unfractionated heparin, are easier to administer, and may not require monitoring. The anticoagulation effect of low-molecular-weight heparins is caused by a combination of inhibition of thrombin generation and inhibition of thrombin activity. Low-molecular-weight heparins have now been evaluated for a number of cardiovascular conditions and have been found to be safe and effective. We review and summarize the existing data regarding the use of low-molecular-weight heparins in cardiovascular diseases, including venous thromboembolism, percutaneous coronary interventions, and acute coronary syndromes such as ST-segment elevation myocardial infarction.

Effects of enteric-coated, low-dose aspirin on parameters of platelet function

BACKGROUND

Aspirin is widely used as an anti-thrombotic drug; however, it has been suggested that enteric-coated formulations of aspirin may be less bioavailable and less effective as anti-thrombotic agents.

AIM

To assess the effect of a formulation of enteric-coated, low-dose (81 mg) aspirin on serum generated thromboxane B2 and platelet aggregation in healthy subjects.

METHODS

Twenty-four subjects participated in a double-blind, randomized, placebo-controlled, parallel-group, multiple-dose study. Twelve subjects in each of two groups received a daily oral dose of enteric-coated aspirin (81 mg) or matching placebo for 7 days. Serum thromboxane B2 and platelet aggregation (using 1 mm arachidonic acid and 1 microg/mL collagen as agonists) were measured 1-3 days prior to day 1, on day 1 (prior to therapy) and 4 h after the last dose on day 7.

RESULTS

After seven daily doses of enteric-coated aspirin, the mean percentage inhibition from baseline of ex vivo generated serum thromboxane B2 was 97.4%, compared with a 7.8% increase after placebo treatment. The mean percentage inhibition of arachidonic acid- and collagen-induced platelet aggregation was 97.9% and 70.9%, respectively, following enteric-coated aspirin, compared with - 1.0% and 2.7%, respectively, after placebo.

CONCLUSIONS

The anti-platelet effects of multiple, daily, low-dose aspirin (as assessed by inhibition of serum thromboxane B2 and platelet aggregation) are not adversely affected by enteric coating.

The failure of orally administered glycoprotein IIb/IIIa inhibitors to prevent recurrent cardiac events

PURPOSE

Despite the success of intravenous glycoprotein IIb/IIIa antagonists, oral formulations have failed to show benefit and have been associated with increased mortality. To understand these findings, we performed a meta-analysis of results from four phase 3 trials.

SUBJECTS AND METHODS

Trials were identified by MEDLINE search; review of abstracts from American College of Cardiology, European Society of Cardiology, and American Heart Association scientific sessions; or querying investigators in the field. Published, phase 3, randomized, placebo-controlled trials involving more than 1000 patients with coronary artery disease that compared an oral glycoprotein IIb/IIIa antagonist with or without background aspirin versus aspirin, and that had a planned follow-up of > or =30 days, were included. Four trials met these criteria. Odds ratios (ORs) and 95% confidence intervals (CIs) were generated from results, and combined using an empirical Bayes random-effects model.

RESULTS

Among 33,326 patients, oral glycoprotein IIb/IIIa agents were associated with 31% increased mortality (OR = 1.31; 95% CI: 1.12 to 1.53; P= 0.0001). Results were similar whether the agent was added to (OR = 1.38; 95% CI: 1.15 to 1.67) or substituted for (OR = 1.37; 95% CI: 1.00 to 1.86) aspirin. Ischemic events or sudden death (OR = 1.22; 95% CI: 0.91 to 1.63) were also more common. Among patients with acute coronary syndromes, the incidence of myocardial infarction was increased (OR = 1.16; 95% CI: 1.03 to 1.29).

CONCLUSION

Oral glycoprotein IIb/IIIa inhibitor therapy is associated with increased mortality and myocardial infarction. No single explanation for these findings is satisfactory; the problem is likely to be multifactorial.

Combined central retinal arterial and venous obstruction: emergency ophthalmic arterial fibrinolysis

PURPOSE

To investigate the role of urokinase selectively perfused into the ophthalmic artery as an emergency treatment for combined central retinal arterial obstruction (CRAO) and central retinal venous obstruction (CRVO).

MATERIALS AND METHODS

Over a 6-year period, 11 consecutive patients presented with recent combined CRAO and CRVO (< or =72 hours). Urokinase (300,000 IU) was selectively perfused via the femoral artery into the ophthalmic artery for 40 minutes. Evaluation criteria were Snellen visual acuity with best correction, funduscopic results, and retinal arteriovenous transit time assessed over a mean 3.5-year follow-up. Mean vision and retinal perfusion were tested by means of repeated-measures analysis of variance. The correlation between visual improvement and retinal perfusion improvement was evaluated by means of Spearman rank correlation.

RESULTS

Substantial improvement in vision and retinal perfusion was noted in seven of the 11 patients treated. Mean vision improvement was significant (P =.009) within 24-48 hours after fibrinolysis, increased until 1 month after (P =.006), then remained stable throughout the follow-up (P >.10). Visual improvement correlated with retinal perfusion improvement during the period from before fibrinolysis to 24-48 hours after (P =.028). In all patients with improved results, retinal hemorrhages transiently increased. One patient had intravitreal hemorrhage shortly after fibrinolysis.

CONCLUSION

For this uncommon clinical entity, which typically has a poor visual outcome, these results suggest that ophthalmic arterial fibrinolysis may restore retinal perfusion, which leads to rapid substantial visual improvement in many cases of combined CRAO and CRVO, without systemic complications, but it may be responsible for intravitreal hemorrhage.

Rationale for the use of platelet aggregation inhibitors in PAD patients

Peripheral arterial disease (PAD) is a major risk marker for systemic ischaemic events. The understanding of PAD has moved from PAD as an organ-specific disease to PAD as the lower-limb localization of a multifocal disease, i.e. atherothrombosis. Blood platelet activation and aggregation is a common denominator in atherothrombotic events, and use of antiplatelet agents in patients with PAD can inhibit thrombus formation and reduce the occurrence of myocardial infarction (MI), ischaemic stroke (IS) and vascular death. Many studies have investigated various antiplatelet regimens for preventing acute cardiovascular events in patients with a prior ischaemic event, although many of these studies had a number of limitations. The Antiplatelet Trialists' Collaboration performed a meta-analysis of 23 stroke trials and found an average odds risk reduction of 25% for a combined endpoint of stroke, MI or vascular death. The concept of atherothrombosis as a multifocal disease was challenged by the Clopidogrel versus Aspirin in Patients at Risk of Ischaemic Events (CAPRIE) trial. This study showed an 8.7% decrease in the relative risk reduction for further atherothrombotic events with clopidogrel over aspirin (p = 0.043) for the overall population, in terms of the combined endpoint of IS, Ml or vascular death.

The role of platelets in peripheral arterial disease: therapeutic implications

Peripheral arterial disease (PAD) is associated with platelet hyperaggregability as well as an increase in morbidity and mortality from myocardial infarction and stroke. Enhanced platelet activation in PAD may substantially contribute to these adverse outcomes. A relative resistance to aspirin therapy has been reported in patients with PAD. Therefore, clopidogrel may be superior to aspirin in treatment of PAD. Furthermore, the aspirin + clopidogrel combination could be more effective than monotherapy but its risk-benefit ratio has yet to be evaluated. Clopidogrel is preferable to ticlopidine because of its safer profile and the convenience of once-daily administration. The glycoprotein (Gp) IIb/IIIa inhibitors may also find a place as short-term therapy after peripheral angioplasty. There is a need to consider the use of clopidogrel in patients who cannot tolerate aspirin. Patients who have an event while taking aspirin also present a problem. One possibility here is to substitute aspirin with clopidogrel or to add clopidogrel to the aspirin. Although these options are currently not evidence based in patients with PAD, there is emerging evidence showing that they are realistic choices.

Nonsteroidal antiinflammatory drugs after acute myocardial infarction

BACKGROUND

Many older patients undergo therapy with nonsteroidal antiinflammatory drugs (NSAIDs), medications that produce effects on platelets and inflammation similar to those produced with aspirin. The impact of these agents on mortality after acute myocardial infarction is not known. We sought to determine whether the use of NSAIDs alone, or in addition to aspirin, is associated with a lower 1-year mortality rate in elderly patients after acute myocardial infarction.

METHODS

We performed an analysis of the Cooperative Cardiovascular Project, a retrospective medical record review that included demographic and clinical information for Medicare beneficiaries hospitalized with a diagnosis of acute myocardial infarction during 1994 and 1995. The cohort included 48,584 elderly patients with acute myocardial infarction without contraindications to NSAID or aspirin therapy. There were 736 patients (1.5%) who were prescribed NSAIDs alone, 36,211 (74.5%) prescribed aspirin alone, 2096 (4.3%) prescribed both NSAIDs and aspirin, and 9541 (19.6%) prescribed neither medication at discharge.

RESULTS

Compared with patients discharged with neither medication, prescriptions of NSAID therapy alone (hazard ratio [HR], 0.77; 95% CI, 0.65-0.90), aspirin alone (HR, 0.81; 95% CI, 0.77-0.86), and both medications (HR, 0.78; 95% CI, 0.69-0.88) were associated with lower adjusted 1-year mortality rates. Compared with patients prescribed NSAID therapy at discharge, there was no significant benefit associated with the addition of aspirin, and the benefit of NSAID therapy was not significantly different from that of aspirin alone.

CONCLUSION

The prescription of NSAID therapy at hospital discharge for elderly Medicare beneficiaries who survived acute myocardial infarction was associated with similarly lower 1-year mortality rates as compared with aspirin therapy. The addition of aspirin to NSAID therapy was not associated with an additional survival benefit.

Cardiovascular thrombotic events in controlled, clinical trials of rofecoxib

BACKGROUND

In comparing aspirin, nonselective nonsteroidal antiinflammatory agents (NSAIDs), and cyclooxygenase (COX)-2 inhibitors, variation in platelet inhibitory effects exists that may be associated with differential risks of cardiovascular (CV) thrombotic events. Among the randomized, controlled trials with the COX-2 inhibitor rofecoxib, one study demonstrated a significant difference between rofecoxib and its NSAID comparator (naproxen) in the risk of CV thrombotic events. A combined analysis of individual patient data was undertaken to determine whether there was an excess of CV thrombotic events in patients treated with rofecoxib compared with those treated with placebo or nonselective NSAIDs.

METHODS AND RESULTS

CV thrombotic events were assessed across 23 phase IIb to V rofecoxib studies. Comparisons were made between patients taking rofecoxib and those taking either placebo, naproxen (an NSAID with near-complete inhibition of platelet function throughout its dosing interval), or another nonselective NSAIDs used in the development program (diclofenac, ibuprofen, and nabumetone). The major outcome measure was the combined end point used by the Antiplatelet Trialists' Collaboration, which includes CV, hemorrhagic, and unknown deaths; nonfatal myocardial infarctions; and nonfatal strokes. More than 28 000 patients, representing >14 000 patient-years at risk, were analyzed. The relative risk for an end point was 0.84 (95% CI: 0.51, 1.38) when comparing rofecoxib with placebo; 0.79 (95% CI: 0.40, 1.55) when comparing rofecoxib with non-naproxen NSAIDs; and 1.69 (95% CI: 1.07, 2.69) when comparing rofecoxib with naproxen.

CONCLUSIONS

This analysis provides no evidence for an excess of CV events for rofecoxib relative to either placebo or the non-naproxen NSAIDs that were studied. Differences observed between rofecoxib and naproxen are likely the result of the antiplatelet effects of the latter agent.

Indobufen: an updated review of its use in the management of atherothrombosis

Indobufen inhibits platelet aggregation by reversibly inhibiting the platelet cyclooxygenase enzyme thereby suppressing thromboxane synthesis. Clinical trials have evaluated the efficacy of oral indobufen in the secondary prevention of thromboembolic complications in patients with or without atrial fibrillation, in the prevention of graft occlusion after coronary artery bypass graft (CABG) surgery and in the treatment of intermittent claudication. In the secondary prevention of thromboembolic events indobufen 200 mg once or twice daily was significantly more effective than no treatment although not as effective as ticlopidine 250 mg once or twice daily, during 1-year nonblind clinical trials. Compared with placebo, indobufen 100 mg twice daily significantly reduced the risk of stroke in a small 28-month trial of patients at increased risk of systemic embolism (50% had atrial fibrillation). Furthermore, in patients with nonrheumatic atrial fibrillation and a recent cerebrovascular event enrolled in the 1-year Studio Italiano Fibrillazione Atriale (SIFA) trial, indobufen 100 or 200 mg twice daily was as effective as warfarin (titrated to produce an international normalised ratio of 2.0 to 3.5) in the secondary prevention of thromboembolic events; the incidences of the composite end-point of major vascular events (10.6 vs 9.0%) and recurrent stroke (5 vs 4%) were similar between treatments. In 2 large 12-month trials, the Studio Indobufene nel Bypass Aortocoronarico (SINBA) and the UK study, indobufen 200 mg twice daily was as effective as aspirin (acetylsalicylic acid) 300 or 325 mg plus dipyridamole 75 mg 3 times daily in the prevention of early and late occlusion of saphenous grafts in patients after CABG surgery. Indobufen 200 mg twice daily for 6 months significantly improved walking capacity compared with placebo, and caused a more pronounced improvement in both pain-free and total walking distance than either pentoxifylline 300 mg or aspirin 500 mg twice daily in separate 6- and 12-month studies of patients with intermittent claudication. Oral indobufen up to 200 mg twice daily was generally well tolerated in >5000 patients with atherosclerotic disease. Adverse events (predominantly gastrointestinal), reported by 3.9% of patients, rarely required withdrawal from treatment. In the SINBA and UK studies, fewer adverse events and less gastrointestinal bleeding were seen with indobufen than with aspirin plus dipyridamole treatment, while in the SIFA trial, noncerebral bleeding events occurred significantly less frequently in indobufen than warfarin recipients (0.6 vs 5.1%) and major bleeding events occurred only in the warfarin group.

CONCLUSION

Indobufen is as effective as warfarin in the prophylaxis of thromboembolic events in at risk patients with nonrheumatic atrial fibrillation, as aspirin plus dipyridamole in the prevention of CABG occlusion and may be more effective than aspirin or pentoxifylline in improving walking capacity in patients with intermittent claudication. The improved tolerability profile of indobufen (favourable gastric tolerance and reduced haemorrhagic complications) compared with aspirin 300 to 325 mg 3 times daily or warfarin, in addition to a similar antiplatelet effect, suggests indobufen can be considered a drug with a definite role in the management of atherothrombotic events. In particular, indobufen may be an effective alternative for at risk patients with nonrheumatic atrial fibrillation in whom anticoagulant therapy is contraindicated or who are at higher risk of bleeding.

Fluorescence spectroscopic analysis of circulating platelet activation during coronary angioplasty

BACKGROUND AND OBJECTIVE

Platelet activation during percutaneous transluminal coronary angioplasty (PTCA) initiates thrombus formation and plaque regrowth at sites of arterial injury, limiting procedure efficacy. We have developed a simple assay for circulating platelet activation based on fluorescence analysis of membrane fluidity and intracellular calcium concentration and light scattering analysis of platelet aggregation.

STUDY DESIGN/MATERIALS AND METHODS

Platelet activation state was measured in 45 patients undergoing angioplasty, before and after treatment with platelet inhibitors.

RESULTS

PTCA alone produced a decrease in pyrene dimer formation (P0.0083) and an increase in light scattering at 650 nm (P0.0128). Treatment with ADP and GPIIb/IIIa receptor antagonists reduced PTCA induced changes in pyrene dimer formation. An unexpected decrease in pyrene dimer formation (P0.05) was detected when the GPIIb/IIIa receptor antagonist was given together with an ADP receptor antagonist.

CONCLUSIONS

1) Analysis of membrane fluidity provides a sensitive marker for platelet activation state. 2) Reduced membrane fluidity after combined platelet inhibitor treatments suggests reduced antiplatelet efficacy.

Antithrombotic Secondary Prevention After Stroke

In patients with transient ischemic attack (TIA) or ischemic stroke of noncardiac origin, antiplatelet drugs are able to decrease the risk of stroke by 11% to 15%, and decrease the risk of stroke, myocardial infarction (MI), and vascular death by 15% to 22%. Aspirin leads to a moderate but significant reduction of stroke, MI, and vascular death in patients with TIA and ischemic stroke. Low doses are as effective as high doses, but are better tolerated in term of gastrointestinal side effects. The recommended aspirin dose, therefore, is between 50 and 325 mg. Bleeding complications are not dose-dependent, and also occur with the lowest doses. The combination of aspirin (25 mg twice daily) with slow release dipyridamole (200 mg twice daily) is superior compared with aspirin alone for stroke prevention. Ticlopidine is effective in secondary stroke prevention in patients with TIA and stroke. For some endpoints, it is superior to aspirin. Due to its side effect profile (neutropenia, thrombotic thrombocytopenic purpura ), ticlopidine should be given to patients who are intolerant of aspirin. Prospective trials have not indicated whether ticlopidine is suggested for patients who have recurrent cerebrovascular events while on aspirin. Clopidogrel has a better safety profile than ticlopidine. Although not investigated in patients with TIA, clopidogrel should also be effective in these patients assuming the same pathophysiology than in patients with stroke. Clopidogrel is second-line treatment in patients intolerant for aspirin, and first-line treatment for patients with stroke and peripheral arterial disease or MI. A frequent clinical problem is patients who are already on aspirin because of coronary heart disease or a prior cerebral ischemic event, and then suffer a first or recurrent TIA or stroke. No single clinical trial has investigated this problem. Therefore, recommendations are not evidence-based. Possible strategies include the following: continue aspirin, add dipyridamole, add clopidogrel, switch to ticlopidine or clopidogrel, or switch to anticoagulation with an International Normalized Ratio (INR) of 2.0 to 3.0. The combination of low-dose warfarin and aspirin was never studied in the secondary prevention of stroke. In patients with a cardiac source of embolism, anticoagulation is recommended with an INR of 2.0 to 3.0. At the present time, anticoagulation with an INR between 3.0 and 4.5 can not be recommended for patients with noncardiac TIA or stroke. Anticoagulation with an INR between 3.0 and 4.5 carries a high bleeding risk. Whether anticoagulation with lower INR is safe and effective is not yet known. Treatment of vascular risk factors should also be performed in secondary stroke prevention.

Antiaggregant and anticoagulant therapy in systemic lupus erythematosus and Hughes' syndrome

Antiaggregant and anticoagulant drugs are essential in the management of the manifestations due to antiphospholipid syndrome (APS) in patients with primary Hughes' syndrome or systemic lupus erythematosus. Coumadin derivatives (warfarin and acenocumarol), heparin and aspirin are used for secondary thromboprophylaxis and treatment of recurrent miscarriage. The available evidence for each indication is reviewed in this paper. There is still debate regarding the optimal intensity of oral anticoagulation, the best drug combination for pregnancy failure in APS and the management of asymptomatic patients with antiphospholipid antibodies.

Unstable angina pectoris and non-Q-wave myocardial infarction

Unstable angina pectoris and non-Q-wave myocardial infarction are clinical syndromes that share many pathophysiologic and clinical features. In the spectrum of coronary artery disease, these syndromes lie between chronic stable angina and Q-wave myocardial infarction. Although both conditions are associated with significant morbidity and mortality, patients presenting with these syndromes can be further risk stratified into higher and lower risk based on a number of readily available clinical features and biochemical parameters. Such risk stratification can allow for more tailored treatment and better resource allocation. Although routine early coronary angiography and revascularization has not been shown to be superior to conservative management, certain high-risk patients may benefit from a more aggressive strategy. Medical therapy with the use of antiplatelet, anticoagulant, and antiischemic agents remains the cornerstone of emergent treatment for patients presenting with these syndromes. The recent demonstration of a reduction in both morbidity and mortality with the glycoprotein IIb/IIIa antagonists has further expanded the armamentarium of available agents. Following initial stabilization, risk stratification with stress testing can help identify patients with a large residual ischemic burden who may benefit from coronary angiography with revascularization if feasible.

Regional anesthesia and anticoagulation

The perioperative use of neuraxial techniques in the presence of anticoagulation is a controversial issue. There are significant pharmacokinetic differences between anticoagulants that will affect the timing of neuraxial needle insertion or catheter removal. The pharmacologic profiles of commonly used anticoagulants in the perioperative period are reviewed. Studies examining the use of neuraxial techniques in the presence of various anticoagulants are reviewed and evaluated in the context of the American Society of Regional Anesthesia consensus statements.

Antiplatelet therapy in the elderly. Aspirin, ticlopidine-clopidogrel, and GPIIb/GPIIIa antagonists

Antiplatelet agents including aspirin, dipyridamole, the thienopyridines, and the GPIIb/IIIa antagonists have collectively demonstrated their ability to have a significant impact on the incidence of recurrent MIs, strokes, and other vascular ischemic events in the geriatric population. Low-dose aspirin also seems to be effective and safe for the primary prevention of ischemic heart disease in men considered at high risk. There is no evidence that the recommendations from these studies had increased relevance to younger adults, and the studies considering age as a variable found antiplatelet agents had either similar or increased benefit in older patients. In view of the relatively reduced adverse effects of these agents when compared with their potential therapeutic benefit, it is important that they be considered in all older patients for secondary prevention and in certain high-risk groups for primary prevention of cardiovascular morbidity and mortality.

Questions regarding future research on aspirin and the gastrointestinal tract

Despite great proven and potential benefits, aspirin also has adverse side effects on all parts of the gastrointestinal tract including ulceration, bleeding, perforation, and stenosis. Because of widespread and growing use, there is a need to understand and, if possible, prevent the adverse effects of aspirin while maintaining its benefits. This article is part of a report from a consensus meeting in 1999 on nonsteroidal anti-inflammatory drugs, and examines possible mechanisms of each of the risks of normal and low-dose aspirin use including areas of uncertainty. Based on these issues, we recommend studies that would further clarify the actions of aspirin. We also examine various strategies that might be used to prevent or mitigate adverse effects. Finally, we propose future research prospects in the search for a safer aspirin.

Aspirin: new cardiovascular uses for an old drug

Inhibition of TXA2-dependent platelet function by aspirin may lead to prevention of thrombosis as well as to excess bleeding. The balance between the two depends critically on the absolute thrombotic versus hemorrhagic risk of the patient. As the risk of experiencing a major vascular event increases, so does the absolute benefit of antiplatelet prophylaxis with aspirin [Figure-see text]. The antithrombotic effect of aspirin does not appear to be dose related over a wide range of daily doses (30 to 1,300 mg), an observation consistent with saturability of platelet COX-1 inhibition by aspirin at very low doses. In contrast, GI toxicity of the drug does appear to be dose related, consistent with dose- and dosing interval-dependent inhibition of COX-1 activity in the nucleated lining cells of the GI mucosa. Thus, aspirin once daily is recommended in all clinical conditions where antiplatelet therapy is effective. Because of safety considerations, physicians are encouraged to use the lowest dose of aspirin shown effective in each clinical setting [Table-see text].

Advances in the pharmacology of acute coronary syndrome. Platelet inhibition

The development of potent inhibitors of platelet aggregation has led to significant decreases in morbidity and mortality rates among patients undergoing percutaneous coronary intervention. Clinical trials have demonstrated that agents that block glycoprotein IIb/IIIa receptor-mediated platelet aggregation have an outcome benefit when used acutely in patients with chest pain and ST depression or elevated cardiac enzymes, leading to the integration of these agents into emergency medicine clinical practice. This article provides an overview of the pathophysiology of acute coronary syndrome and the pharmacology of platelet inhibition and reviews the evidence from the clinical trials pertaining to the use of these agents in the emergency department.

Acute antithrombotic effect of a front-loaded regimen of clopidogrel in patients with atherosclerosis on aspirin

There is a need for a rapid antithrombotic effect after the administration of antiplatelet drugs in the setting of acute coronary syndromes and percutaneous interventions. Clopidogrel, a new thienopyridine derivative, is an efficient antiplatelet agent. However, the standard regimen of clopidogrel (75 mg/d) requires 2 to 3 days before significant antithrombotic effects. Patients with stable arterial disease on chronic aspirin therapy (n=20) were treated with clopidogrel either with a front-loaded regimen, 300 mg the first day and 75 mg/d the next 7 days, or with a standard regimen, 75 mg/d for 8 days. Blood thrombogenicity was assessed by quantification of platelet-thrombus formation in an ex vivo perfusion chamber, by ADP-induced platelet aggregation, and by ADP-induced fibrinogen binding. At 2 hours, mean total thrombus area with the standard regimen was not significantly reduced. In contrast, at 2 hours, the mean total thrombus area with the front-loaded regimen was significantly decreased by 23.1+/-8.5% versus baseline (P<0.05). ADP-induced platelet aggregation (with 5 and 10 micromol/L) was also significantly (P<0.05) reduced with the front-loaded regimen at 2 hours, with the mean platelet aggregation being 82.2+/-4.4% and 81.8+/-4.5%, respectively, versus baseline. Similarly, flow cytometry demonstrated a significant decrease (P<0. 05) in the ADP-induced fibrinogen binding (with 0.12 and 0.6 micromol/L) at 2 hours in this front-loaded regimen group (36.1+/-2. 0% and 53.2+/-9.3%). With the standard regimen, platelet activity was not significantly reduced at 2 hours. Our data suggest that a front-loaded regimen of clopidogrel added to aspirin achieves a significant antithrombotic effect at 2 hours in patients with known atherosclerotic disease on chronic aspirin therapy. This provides a rationale for using front-loaded clopidogrel in combination with aspirin in percutaneous coronary interventions.

Antithrombotic Therapy during and after Intracoronary Stenting

Objective:

To evaluate the impact on patient outcomes of antithrombotic therapy during and after intracoronary stenting.

Data Sources:

A MEDLINE search (1966-July 2000) for English-language clinical trials and review articles using the search terms stent and coronary with one or more of the following search terms: abciximab, tirofiban, orofiban, xemilofiban, eptifibatide, aspirin, heparin, enoxaparin, tinzaparin, dalteparin, hirudin, danaparoid, dipyridamole, cilostazol, dextran, warfarin, anticoagulant, ticlopidine, and Clopidogrel. References from these articles were reviewed for additional articles. Pharmaceutical companies were contacted to identify unpublished studies. A total of 177 sources were initially identified.

Study Selection:

Studies were selected through an unblinded individual review for prospective, randomized clinical trials evaluating patient outcomes related to antithrombotic therapy during or after intracoronary stent placement. Additional human and animal studies were included for background and introductory information.

Data Extraction:

Patient characteristics in each study were compared with those of the overall stent population. The primary end point measurements were defined. The completeness of follow-up and power analysis was assessed.

Data Synthesis:

Intracoronary stenting is now a common modality for maintaining patency of occluded arteries. Antithrombotic therapy during coronary artery stent placement is changing as knowledge about the pathophysiology of thrombus formation expands and new medications become available. Development of new stent placement techniques, new stent designs, and methods of restenosis irradiation or prevention have coincided with evolving antithrombotic regimens.

Conclusions:

The current antithrombotic regimen used in coronary artery stenting is complex, but has a lower incidence of hemorrhagic complications and thrombosis compared with previous anticoagulant regimens. Antithrombotic therapy may need to be tailored to individual patient contraindications.

Differential effects of aspirin and non-aspirin nonsteroidal antiinflammatory drugs in the primary prevention of myocardial infarction in postmenopausal women

The antiplatelet effect of aspirin reduces the risk of clinical manifestations of atherothrombosis by approximately 25% in secondary prevention settings. Data are limited in primary prevention of coronary heart disease, and even more in women. Here, we estimate the effects of aspirin and non-aspirin nonsteroidal antiinflammatory drugs in the primary prevention of myocardial infarction in postmenopausal women. We followed a cohort of 164,769 women, 50-74 years of age, registered in the General Practice Research Database in the United Kingdom, from January 1991 through December 1995. For aspirin and non-aspirin nonsteroidal antiinflammatory drugs, the risk of myocardial infarction associated with current use was compared with risk in non-users, using a nested case-control analysis. Overall, the relative risk of myocardial infarction associated with current use of aspirin of more than 1 month's duration was 0.56 [95% confidence interval (95% CI) = 0.26-1.21], and that of nonfatal myocardial infarction was 0.28 (95% CI = 0.08-0.91). Chronic use of nonsteroidal antiinflammatory drugs was not associated with a protective effect (relative risk = 1.32; 95% CI = 0.97-1.81). These findings indicate that incomplete and reversible inhibition of platelet cyclooxygenase by non-aspirin nonsteroidal antiinflammatory drugs is not sufficient to produce clinically detectable cardiovascular protection comparable with that achieved by low-dose aspirin through irreversible inactivation of platelet cyclooxygenase.

Cardiac Causes of Stroke

At least 20% of all ischemic strokes are cardioembolic. Cardiac conditions that cause cerebral embolism are classified as major or minor depending on whether the causal link has or has not been fully established between the underlying cardiac condition and the stroke. Atrial fibrillation, acute myocardial infarction, valvular heart disease, infective endocarditis, nonbacterial thrombotic endocarditis, and atrial myxoma are the main cardiac causes of cerebral embolism. Patent foramen ovale, atrial septal aneurysm, mitral valve prolapse, mitral annular calcification, calcific aortic stenosis, and mitral valve strands are cardiac conditions with a potential causal link to cerebral embolism, but until now, either they have been found to be poor predictors of recurrent stroke or their risk of recurrent stroke is unknown. The management of patients with a stroke of cardiac source is twofold: 1) treatment of the acute phase of stroke and 2) prophylactic treatment of recurrent thromboembolism. When possible, primary prevention of cerebral embolism should be recommended, particularly in cardiac conditions with known high risk of stroke (eg, atrial fibrillation, mitral stenosis, or presence of mechanical prosthetic heart valves).

Early potent antithrombotic effect with combined aspirin and a loading dose of clopidogrel on experimental arterial thrombogenesis in humans

BACKGROUND

We conducted a double-blind, randomized, crossover study to assess the antithrombotic effects of the combination of aspirin (acetylsalicylic acid, ASA) and clopidogrel, with or without a loading dose, versus ASA alone in a model of arterial thrombosis in humans.

METHODS AND RESULTS

Eighteen male volunteers received the following 3 regimens for 10 days separated by a 1-month period: (1) 325 mg ASA daily, (2) 325 mg ASA+75 mg clopidogrel daily, (3) 325 mg ASA daily+300-mg clopidogrel loading dose on day 1 and +75 mg clopidogrel per day on days 2 to 10. The antithrombotic effect was measured 1.5, 6, and 24 hours after drug intake on day 1 and 6 hours after drug intake on day 10. Arterial thrombus formation was induced ex vivo by exposing a collagen-coated coverslip in a parallel-plate perfusion chamber to native blood for 3 minutes at an arterial wall shear rate. Without a loading dose, clopidogrel+ASA developed an antithrombotic effect within 6 hours after the first intake. It was superior to that produced by ASA, but it was moderate (P</=0.03). However, with the loading dose, the antithrombotic effect of clopidogrel+ASA appeared within 90 minutes, and after 6 hours it was comparable to that on day 10. On day 10, clopidogrel+ASA decreased platelet thrombus formation by approximately 70%, and the effect was significantly more potent than that produced by ASA alone (P<0.001).

CONCLUSIONS

This study confirms the synergistic antithrombotic effects of a combined ASA and clopidogrel therapy and shows the early benefit obtained with a loading dose of clopidogrel.