Apixaban is an orally active inhibitor of coagulation factor Xa with anticoagulant activity. Apixaban directly inhibits factor Xa, thereby interfering with the conversion of prothrombin to thrombin and preventing formation of cross-linked fibrin clots. Apixaban has been available in Europe since May 2012. An FDA decision on apixaban which was expected on June 28, 2012 was initially delayed before final approval on December 28, 2012. On August 21, 2014, Pfizer announced that apixaban was now FDA approved for treatment and secondary prophylaxis of deep vein thrombosis (DVT) and pulmonary embolism (PE). It is being developed in a joint venture by Pfizer and Bristol-Myers Squibb. It has also been used to lower the risk of developing venous thrombosis post-orthopedic surgical procedures.

Ticagrelor (known trade names Brilinta, Brilique and Possia) is a P2Y12 platelet inhibitor. Brilinta has been approved by the US Food and Drug administration (FDA) in 2011 and is indicated to reduce the rate of cardiovascular death, myocardial infarction, and stroke in patients with acute coronary syndrome (ACS) or a history of myocardial infarction. Brilinta also reduces the rate of stent thrombosis in patients who have been stented for treatment of ACS. Ticagrelor and its major metabolite reversibly interact with the platelet P2Y12 ADP-receptor to prevent signal transduction and platelet activation. Ticagrelor and its active metabolite are approximately equipotent. In vitro metabolism studies demonstrate that ticagrelor and its major active metabolite are weak inhibitors of CYP3A4, potential activators of CYP3A5 and inhibitors of the P-gp transporter. Most common adverse reactions are bleeding 12% and dyspnea 14%.

Rivaroxaban (trade name Xarelto) is an oral anticoagulant. It is the first available orally active direct factor Xa inhibitor. Upon oral administration, rivaroxaban selectively binds to both free factor Xa and factor Xa bound in the prothrombinase complex. This interferes with the conversion of prothrombin (factor II) to thrombin and eventually prevents the formation of cross-linked fibrin clots. Rivaroxaban does not affect existing thrombin levels. Activation of factor X to factor Xa (FXa) via the intrinsic and extrinsic pathways plays a central role in the cascade of blood coagulation. Xarelto is indicated to reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation, treatment and prophylaxis of deep vein thrombosis (DVT) which may lead to PE in patients undergoing knee or hip replacement surgery, pulmonary embolism (PE) and for the reduction in the risk of recurrence of deep vein thrombosis and of pulmonary embolism following initial 6 months treatment for DVT and/or PE.

Dabigatran (Pradaxa, Prazaxa) is an anticoagulant medication that can be taken by mouth. FDA approved on October 19, 2010. Dabigatran directly inhibits thrombin in a concentration-dependent, reversible, specific, and competitive manner which results in a prolongation of aPTT (partial thromboplastin time), ECT (Ecarin clotting time), and TT (thrombin time). It may increase INR but this laboratory parameter is relatively insensitive to the activity of dabigatran. Dabigatran is indicated for the prevention of venous thromboembolic events in patients who have undergone elective hip or knee replacement surgery (based on RE-NOVATE, RE-MODEL, and RE-MOBILIZE trials). In 2010, it was approved in the US and Canada for prevention of stroke and systemic embolism in patients with atrial fibrillation (approval based on the RE-LY trial). Contraindications: severe renal impairment (CrCL < 30 ml/min); haemorrhagic manifestations, bleeding diathesis or spontaneous or pharmacologic impairment of haemostasis; lesions at risk of clinically significant bleeding (e.g. extensive cerebral infarction (haemorrhagic or ischemic) in the last 6 months, active peptic ulcer disease); concomitant treatment with P-glycoprotein inhibitors (e.g. oral ketoconazole, verapamil); and those with known hypersensitivity to dabigatran, dabigatran etexilate or any ingredient used in the formulation or component of the container. As of December 2012, dabigatran is contraindicated in patients with mechanical prosthetic heart valves.

Fondaparinux is a synthetic and specific inhibitor of activated Factor X (Xa). By selectively binding to antithrombin III (ATIII), fondaparinux sodium potentiates (about 300 times) the innate neutralization of Factor Xa by ATIII. Neutralization of Factor Xa interrupts the blood coagulation cascade and thus inhibits thrombin formation and thrombus development. Fondaparinux is indicated for the prophylaxis of deep vein thrombosis (DVT), which may lead to pulmonary embolism (PE): in patients undergoing hip fracture surgery, including extended prophylaxis; in patients undergoing hip replacement surgery; in patients undergoing knee replacement surgery; in patients undergoing abdominal surgery who are at risk for thromboembolic complications. The most serious adverse reactions reported with Fondaparinux are bleeding complications and thrombocytopenia. Agents that may enhance the risk of hemorrhage should be discontinued prior to initiation of therapy with Fondaparinux unless these agents are essential.

Tirofiban is a non-peptide antagonist of the platelet glycoprotein (GP) IIb/IIIa receptor. Tirofiban is a reversible, competitive inhibitor of GP IIb/IIIa receptors, exerting its effects via the prevention of the binding of fibrinogen and other ligands, resulting in the inhibition of the last common step of thrombi formation. Tirofiban was discovered by Merck, USA, and was approved by the FDA in 1998 under the trade name AGGRASTAT. AGGRASTAT, in combination with heparin, is indicated for the treatment of acute coronary syndrome, including patients who are to be managed medically and those undergoing percutaneous transluminal coronary angioplasty or atherectomy. AGGRASTAT reduces the risk of ischaemic complications in patients with unstable angina/non-Q-wave myocardial infarction and high-risk patients undergoing revascularisation when used against a background of heparin and aspirin. Furthermore, the drug has an acceptable tolerability profile. Therefore, intravenous tirofiban is likely to be used as an adjunct to heparin and aspirin in patients with acute coronary syndromes including high-risk patients undergoing revascularisation.

Clopidogrel, an antiplatelet agent structurally and pharmacologically similar to ticlopidine, is used to inhibit blood clots in a variety of conditions such as peripheral vascular disease, coronary artery disease, and cerebrovascular disease. Clopidogrel is sold under the name Plavix by Sanofi and Bristol-Myers Squibb. Plavix (clopidogrel bisulfate) is an inhibitor of ADP-induced platelet aggregation acting by direct inhibition of adenosine diphosphate (ADP) binding to its receptor and of the subsequent ADPmediated activation of the glycoprotein GPIIb/IIIa complex. Clopidogrel must be metabolized by CYP450 enzymes to produce the active metabolite that inhibits platelet aggregation. The active metabolite of clopidogrel selectively inhibits the binding of adenosine diphosphate (ADP) to its platelet P2Y12 receptor and the subsequent ADPmediated activation of the glycoprotein GPIIb/IIIa complex, thereby inhibiting platelet aggregation. This action is irreversible. Consequently, platelets exposed to clopidogrel’s active metabolite are affected for the remainder of their lifespan (about 7 to 10 days). Platelet aggregation induced by agonists other than ADP is also inhibited by blocking the amplification of platelet activation by released ADP. Plavix (clopidogrel bisulfate) is indicated for the reduction of atherothrombotic events.

Ticlopidine (trade name Ticlid) is an antiplatelet drug in the thienopyridine family which is an adenosine diphosphate (ADP) receptor inhibitor. Ticlopidine is a prodrug that is metabolized to an as yet undetermined metabolite that acts as a platelet aggregation inhibitor. Inhibition of platelet aggregation causes a prolongation of bleeding time. In its prodrug form, ticlopidine has no significance in vitro activity at the concentrations attained in vivo. The active metabolite of ticlopidine prevents binding of adenosine diphosphate (ADP) to its platelet receptor, impairing the ADP-mediated activation of the glycoprotein GPIIb/IIIa complex. It is proposed that the inhibition involves a defect in the mobilization from the storage sites of the platelet granules to the outer membrane. No direct interference occurs with the GPIIb/IIIa receptor. As the glycoprotein GPIIb/IIIa complex is the major receptor for fibrinogen, its impaired activation prevents fibrinogen binding to platelets and inhibits platelet aggregation. Ticlopidine is FDA approved for the prevention of strokes and, when combined with aspirin, for patients with a new coronary stent to prevent closure. There are also several off-label uses, including acute treatment of myocardial infarction and unstable angina, peripheral vascular disease, prevention of myocardial infarctions, diabetic retinopathy, and sickle cell disease. The most serious side effects associated with ticlopidine are those that affect the blood cells, although these life-threatening complications are relatively rare.

Warfarin is an anticoagulant drug normally used to prevent blood clot formation as well as migration. Warfarin is marketed under the brand name Coumadin among others. Coumadin (crystalline warfarin sodium) is an anticoagulant which acts by inhibiting vitamin K-dependent coagulation factors. Chemically, it is 3-(α-acetonylbenzyl)-4-hydroxycoumarin and is a racemic mixture of the R- and S-enantiomers. Coumadin is indicated for the prophylaxis and/or treatment of venous thrombosis and its extension, and pulmonary embolism. It is also indicated for the prophylaxis and/or treatment of the thromboembolic complications associated with atrial fibrillation and/or cardiac valve replacement. Warfarin is thought to interfere with clotting factor synthesis by inhibition of the C1 subunit of the vitamin K epoxide reductase (VKORC1) enzyme complex, thereby reducing the regeneration of vitamin K1 epoxide. The degree of depression is dependent upon the dosage administered and, in part, by the patient’s VKORC1 genotype. Therapeutic doses of warfarin decrease the total amount of the active form of each vitamin K dependent clotting factor made by the liver by approximately 30% to 50%.