Antiplatelet Agents – Mild Blood Thinners
Platelets are blood cells that are help the blood clot (stick together) and prevent bleeding. When the body has a cut, scratch, bruise, or bleed, platelets go into action and begin to work. They can be thought of as materials (like bricks or blocks) that aggregate (link together/ stack up) to form this clot. These platelet cells need thromoxane A2, adenosine, vitamin K specific clotting factors (chemicals produced by the body) to make them aggregate (stick) together. These chemicals can be thought of as the glue that holds the blocks together to make the clot. However, in patients who have had a TIA or stroke, the blocks don’t need to stick together as much because this causes the blood to be too thick (like adding flour to milk when making a cake batter it makes it thicker and harder to stir or pour) and possibly form a clot that can’t fit through the vessels.
So, doctors often place stroke/TIA patients on blood thinners to decrease the possibility of the body forming another clot in the blood, which may lead to another TIA or stroke.
- Aspirin is used for prophylaxis of TIA and/or stroke except in patients with an allergy to aspirin or salicylates.
- The mechanism of action for aspirin’s stroke prevention is the inhibition of prostaglandin synthesis action to prevent the formation of platelet-aggregating substance thromboxane A2.
- The usual dose for this indication in adults is 50 – 325mg/day. Aspirin should be taken with food, milk, or large glass of water to decrease GI problems. Monitor for signs of bleeding.
Aspirin and Dipyridamole – Aggrenox®
- Aggrenox® is used to reduce the risk of stroke in patients who have had a TIA or completed ischemic stroke due to thrombosis, except in patients with hypersensitivity to dipyridamole or aspirin.
- The mechanism for its antithrombotic action is the additive antiplatelet effect of the two drugs. The aspirin portion works the inhibition of prostaglandin synthesis action to prevent the formation of platelet-aggregating substance thromboxane A2, while the dipyridamole inhibits adenosine uptake into erythrocytes, endothelial cells, and platelets.
- One capsule (aspirin 25mg and dipyridamole 200mg) twice a day is the usual dose in adults. The capsule should be swallowed whole (not chewed or crushed), and can be taken with or without food. Most patients experience a severe headache when initiating therapy due to the vasodilatation of dipyridamole. The headache should ease and resolve after the body adjusts to the treatment. In the mean time, acetaminophen (Tylenol) is the treatment of choice for the headache.
Clopidogrel – Plavix®
- Clopidogrel is used to reduce future atherosclerotic events (stroke) in patients with a recent stroke.
- The drug’s mechanism is it blocks the adenosine phosphate (ADP) receptors, which prevents fibrinogen binding to the receptor. This decreases the ability of platelet adhesion and aggregation.
- The usual dose for stroke prevention is 75mg once a day, and can be taken without food. It may be used as an alternative to aspirin containing products in patients allergic to aspirin or salicylates.
Clopidogrel and Aspirin
- The combination of clopidogrel and aspirin is used to reduce future atherosclerotic events (stroke) in patients with a recent stroke or patients who had a stroke while on clopidogrel.
- The mechanism of action for each drug is different. Clopidogrel blocks the adenosine phosphate (ADP) receptors, which prevents fibrinogen binding to the receptor, while aspirin inhibits prostaglandin synthesis action to prevent the formation of platelet-aggregating substance thromboxane A2.
- The usual dose is clopidogrel 75mg tablet and an additional aspirin 325mg tablet a day. Patients may need to take the medications with food, milk, or a full glass of water to decrease GI problems. Do not dispense in aspirin/salicylate allergic patients.
Ticlopidine – Ticlid®
- Ticlopidine is used in patients to decrease the risk of stroke or the occurrence of another stroke. However, due to its life-threatening rheumatologic disorders, it should be reserved for patients refractory to aspirin or allergic to aspirin.
- The mechanism of action is unique among the antiplatelet drugs because it specifically increases bleeding time.
- The usual dose is 250mg twice a day. It should be taken with food to decrease stomach upset.
- Starting the second week of therapy and through the third month of therapy, patients will need a complete blood count with differential every two weeks. The peak occurrence of thrombocytopenia (TTP) is 3-4 weeks after starting the medicine, with peak occurrences of neutropenia at 4-6 weeks, and aplastic anemia incidences after 4-8 weeks.
Oral Anticoagulant – Stronger Blood Thinners
Warfarin – Coumadin®
- Warfarin is used for the treatment and prophylaxis of pulmonary embolism, venous thrombosis, and thromboembolic disorders, and to prevent recurrences of TIA’s. In stroke patients, warfarin is most often used to prevent a cardiogenic embolism due to atrial fibrillation.
- The usual therapy for the prevention of a cardioembolic TIA or stroke in patient with atrial fibrillation is long term oral anticoagulation with a target international normalized ratio (INR) of 2.5 (range of 2.0-3.0)
- Warfarin’s mechanism of action is interference with hepatic synthesis of vitamin K-dependent coagulation factors (II, VII, IX, and X). Foods high in vitamin K inhibit the effects of warfarin. Once patient is stabilized on warfarin, the patient should not change dietary habits. The patient needs to maintain a consistent amount of vitamin K (70-140mcg/day) in their diet. Foods that are high in vitamin K include: leafy green vegetables, pork and beef liver, and green teas. Patients should be instructed to avoid large amounts of alfalfa, broccoli, asparagus, Brussels sprouts, cauliflower, cabbage, kale, spinach, watercress, lettuce, and turnip greens, and to consult their pharmacist or doctor who monitors their warfarin therapy.
- Patients beginning warfarin will need to have weekly laboratory test done to evaluate and stabilize their therapy.