Management of Thrombotic and Cardiovascular Disorders in the New Millenium

Abstract

Anticoagulants and antithrombotic drugs have played a key role in the prophylaxis, treatment and surgical/interventional management of thrombotic and cardiovascular disorders. There are several newer drugs which are currently developed for the anticoagulant management of cardiovascular diseases in both the medical and surgical indications. These include the low molecular weight heparins (LMWHs), antithrombin agents such as the Hirudin, Hirulog and Argatroban and indirect and direct anti-Xa drugs, represented by Pentasaccharide (Arixtra®) and DX 9065a, respectively. Several other agents such as the natural and recombinant anti-Xa drugs and anti-tissue factor agents are also developed. The antiplatelet agents include Clopidogrel, Cilostazol, Anplag and GP IIb/IIIa inhibitors. For the subcutaneous indications, unfractionated heparin is gradually replaced by the low molecular weight heparins (LMWHs). LMWHs such as the Enoxaparin and Dalteparin are commonly used for the management of acute coronary syndrome. These drugs have been approved for the treatment of unstable angina and are currently undergoing rigorous trials for interventional indications. Arixtras® is also developed for various subcutaneous indications. However, it exhibits lower anticoagulant effects and may not be optimal for intravenous and interventional purposes. At a higher dosage when administered intravenously the LMWHs produce varying degrees of anticoagulation at relatively lower activated clotting times (150-200). Several studies in vascular and cardiovascular interventions have shown that even at a relatively lower anticoagulant level the LMWHs are as effective as unfractionated heparin at the recommended dosages which produce a relatively higher level of anticoagulation (ACT > 200 secs.). Thus, these agents are currently developed for interventional and surgical indications. It should be emphasized that different LMWHs produce different degrees of anticoagulation and should therefore be individually optimized for a given interventional or surgical purposes. At a relatively high dosage the levels of LMWHs can be measured by using the ACT and APTT. When administered with such GP IIb/IIIa inhibitors as the Abciximab, Aggrastat or Eptifibratide, these drugs may require dosage adjustment. However, since the introduction of the front loading of Clopidogrel, the unqualified use of GP IIb/IIIa is debated. LMWHs will find expanded indications in both the medical and surgical management of patients with cardiovascular disorders including atrial fibrillation and congestive heart failure. The only approved anti-Xa drug is represented by a synthetic heparinomimetic, namely, Arixtra®. This drug is given for the prophylaxis of post orthopedic indications. This agent is undergoing additional clinical trials in the management of coronary artery diseases. Because of the dependence on antithrombin III (AT) and the sole anti-Xa effects, it has a narrow therapeutic index and its efficacy in this indication may be limited. Additional clinical trials are needed at this time to validate the clinical potential of this drug. The antithrombin agents (Hirudin, Hirulog and Argatroban) were initially developed for arterial indications. However, these agents are approved as a substitute anticoagulant in patients with heparin induced thrombocytopenia (HIT) and PCI. Currently all of these agents are being developed for surgical and interventional use. However, since there is no available antidote at this time, the development is somewhat limited. The antithrombin agents may be useful in patients with HIT which require further clinical validation. Many other anti-Xa agents are also developed. Most of these can be given parenterally. However, the clinical data is somewhat limited. Similarly, several of the new antiplatelet drugs can be administered parenterally and may be useful in CAD. Since most of these newer anticoagulant and antithrombotic drugs are mono-therapeutic their therapeutic index is rather limited. Only in combination these agents can mimic heparins. At this time it is safe to state that heparin and its LMW derivatives will remain the anticoagulant of choice for cardiovascular indications until these newer agents have been validated in extended dinical trials in polytherapeutc settings.