Aspirin thrombosis prophylaxis

Acetylsaliqrlic acid (aspirin) for prophylaxis of thrombosis 5-80% (highly variable increases with increased urinary pH) 80-90 0.1-0.2 2 (salicylate)/ unchanged 75-325 mg q24h 75-325 mg q24 h not recommended ... 

The ACCP Conference on Antithrombotic Therapy recommended against the use of aspirin as the primary method of VTE prophylaxis.2 Antiplatelet drugs clearly reduce the risk of coronary artery and cerebrovascular events in patients with arterial disease, but aspirin produces a very modest reduction in VTE following orthopedic surgeries of the lower extremities. The relative contribution of venous stasis in the pathogenesis of venous thrombosis compared with that of platelets in arterial thrombosis likely explains the reason for this difference. 

Dipyridamole (Persantine) is a vasodilator that, in combination with warfarin, inhibits embolization from prosthetic heart valves and, in combination with aspirin, reduces thrombosis in patients with thrombotic diseases. Dipyridamole by itself has little or no benefit in fact, in trials where a regimen of dipyridamole plus aspirin was compared with aspirin alone, dipyridamole provided no additional beneficial effect. Dipyridamole interferes with platelet function by increasing the cellular concentration of adenosine 3, 5 -monophosphate (cyclic AMP). This effect is mediated by inhibition of cyclic nucleotide phosphodiesterase and by blockade of uptake of adenosine, which acts at A2 receptors for adenosine to stimulate platelet adenylyl cyclase. The only current recommended use of dipyridamole is for primary prophylaxis of thromboemboli in patients with prosthetic heart valves the drug is given in combination with warfarin. 

Many fruits contain salicylates, which inhihit the synthesis of thromboxane A2, and have an anticoagulant action, in amounts that provide the same intake as the low dose of aspirin used as prophylaxis against thrombosis. 

LMW heparins have become the preferred drugs for perioperative prophylaxis because of their convenience. They are as effective and safe as unfractionated heparin at preventing venous thrombosis (see above). Once-daily s.c. administration suffices, as their duration of action is longer than that of conventional heparin and no laboratory monitoring is required. LMW heparins are at least as effective as standard heparin for unstable angina, in combination with aspirin. 

One case-control study showed no increased risk of intracerebral hemorrhage in patients using aspirin or other NSAIDs in low dosages as prophylaxis against thrombosis (21). However, intracerebral hemorrhage has been reported with aspirin, even in low doses, and in the SALT study (22) and the Physicians Health Study of 1989 (23) hemorrhagic stroke and associated deaths occurred with aspirin. 

As mentioned earlier, the presence of antiphospholipid antibodies may result in several clinical manifestations, including thrombosis. There is no agreement on prophylaxis of patients with antiphospholipid antibodies without a history of thromboembolism. In such patients, low-dose aspirin (100-325 mg/day) may be used prophylactically, although efficacy has not been established. Patients with an acute thrombotic event should receive standard treatment with anticoagulants (e.g., heparin). Follow-up treatment with warfarin to prevent recurrence may require an international normahzed ratio (INR) of 3 or greater in patients with antiphosphohpid syndrome. However, currently, there is no consensus on the intensity of anticoagulation or duration of secondary prophylaxis, but since recurrence is common, patients usually are treated with oral anticoagulants indefinitely. ... 

Dalteparin is a low-molecular-weight heparin that inhibits reactions that lead to clotting. Dalteparin sodium is indicated in the prophylaxis of deep vein thrombosis (DVT), which may lead to pulmonary embohsm in patients undergoing hip replacement surgery or in patients undergoing abdominal surgery who are at risk for thromboembolic complications and prophylaxis of ischemic comphcations in unstable angina and non-Q-wave myocardial infarction (MI) in patients on aspirin therapy. 

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