A nurse is preparing to administer alteplase, a thrombolytic drug, to a client who has an acute myocardial infarction. The nurse knows that this drug works by which mechanism?

Alteplase works by activating plasminogen, which converts to plasmin, an enzyme that degrades fibrin.Fibrin is a protein that forms the meshwork of a blood clot, so by breaking it down, alteplase helps dissolve the clot and restore blood flow.

Choice A is wrong because alteplase does not inhibit platelet aggregation and adhesion.

Platelets are blood cells that stick together and form the initial plug in a blood clot.Alteplase does not affect platelets directly, but rather targets fibrin.

Choice B is wrong because alteplase does not interfere with the coagulation cascade.

The coagulation cascade is a series of reactions that lead to the formation of fibrin from fibrinogen.Alteplase does not inhibit any of the steps in this process, but rather activates plasminogen, which is already present in the blood.

Choice D is wrong because alteplase does not block the action of platelet activators or receptors.

Platelet activators are substances that stimulate platelets to aggregate and adhere, such as thrombin, ADP, and collagen.

Platelet receptors are molecules on the surface of platelets that bind to these activators or to other platelets, such as GPIIb/IIIa and GPVI.Alteplase does not affect these molecules, but rather targets fibrin.

The INR is a standardized measure of the prothrombin time (PT), which reflects the activity of the extrinsic and common pathways of coagulation.

Warfarin is an anticoagulant that inhibits the synthesis of vitamin K-dependent clotting factors (II, VII, IX, and X), which are involved in these pathways.

Therefore, the INR is used to monitor the effectiveness of warfarin therapy and adjust the dose accordingly.The target INR range depends on the indication for warfarin, but it is usually between 2 and 3.

Choice A is wrong because activated partial thromboplastin time (aPTT) reflects the activity of the intrinsic and common pathways of coagulation.

Heparin is an anticoagulant that enhances the activity of antithrombin, which inhibits factors II, IX, X, XI, and XII, which are involved in these pathways.Therefore, the aPTT is used to monitor the effectiveness of heparin therapy.

Choice C is wrong because platelet count measures the number of platelets in the blood, which are involved in primary hemostasis.Platelet count is not affected by warfarin therapy, but it can be decreased by heparin-induced thrombocytopenia (HIT), a rare but serious complication of heparin therapy.

Choice D is wrong because fibrinogen level measures the amount of fibrinogen in the blood, which is a precursor of fibrin, the main component of blood clots.Fibrinogen level is not affected by warfarin therapy, but it can be decreased by disseminated intravascular coagulation (DIC), a condition where widespread clotting and bleeding occur simultaneously.

The normal ranges for these tests are as follows:

• INR: 0.8 to 1.2

• aPTT: 25 to 35 seconds

• Platelet count: 150 to 450 x 10^9/L

• Fibrinogen level: 2 to 4 g/L