Anitplatelet drugs include the well known NSAID aspirin, as well as newer lesser known drugs such as clopidogrel, dipryidamole, pentoxifylline, and eptifibatide. For the purposes of my discussion, and to hopefully not put to sleep the majority of people who are going to read this, I'll stick to aspirin and clopiddogrel(Plavix).
How Do Antiplatelets Work?
Antiplatlet drugs by work by manipulating the cyclooxygenase(COX) pathway. Their action on this pathway prevents the aggregation, or clumping together, of platelets that is normally meant to be a protective measure by the body. Aspirin works by irreversibly inhibiting the production of prostaglandins and thromboxanes(TXA2). TXA2 is a substance that causes platelets to bind together and blood vessels to narrow. So conversely, it makes sense that taking aspirin would dilate blood vessels and work against the beginning of clot formation by platelets. Clopidogrel, on the other hand, works on the platelet membrane. It belongs to a class of antiplatelets referred to as ADP inhibitors. Its mode of action prevents the platelet from accepting a chemical message, called fibrinogen, that tells it to clot. Clopidogrel blocks this message by altering the GP IIb/IIIa receptor site on the platelet membrane. This is, of course, a simplified version of the mechanism of action for both drugs shown below.
Antiplatelet Administration
Again, it depends on who you ask. There is no accepted across the board dosage for antiplatelet drugs that is prescribed specifically for the prevention of VTEs. In fact, in regards to aspirin there is a prevailing school of thought that aspirin alone may a have little to no affect in preventing VTEs. Although, as recently as 2008 the U.S. Surgeon General has said that taking up to 150 mg of aspirin a day can be a good preventive measure for VTEs(Galson 2008). The same U.S. Surgeon General along with U.S. Department of Health & Human Services and several other leaders in the field have also called for the need of more research on the specific issue of aspirin's effectiveness in preventing VTEs. In the research I've done, the dosages for aspirin have ranged from as little as 30mg to over 325mg a day, but are usually accompanied by another form of anticoagulant when prescribed for VTE prophylaxis. Clopidogrel is usually started with a single 300-mg loading dose and then given at 75 mg once a day no matter what it is prescribed for. There seems to be more uniformity in the prescribed doses of clopidogrel vs. that of aspirin, as well as a belief that clopidogrel has a better success of preventing VTEs. However, these two drugs are often prescribed together in varying dosages. Once put on antiplatelets for the prevention of a VTE patients, especially those at high risk, may never stop taking them.
Are Antiplatelets Safe?
It is interesting that prostoglandin inhibition is what gives aspirin its beneficial as well as its undesirable effects. Of these undesirable-effects the most common are "gastrointestinal intolerance (including nausea, vomiting, indigestion, gastric ulceration and upper gastrointestinal bleeding), bleeding and renal dysfunction" (Mueller 2004). Another well know issue with aspirin therapy is the belief that children are more susceptible to Reye's syndrome when given aspirin while recovering from a virus. But they still call an 81mg dose "baby aspirin"? This is usually not an issue in regards to VTE prophylaxis, in that children are normally not at risk, and those who are do not receive aspirin. What needs to be the highest concern for those prescribing, administering, and taking aspirin and clopidogrel, as with any anticoagulant, is the increased risk of a bleeding episode (Liley, Harrington, Snyder 2007).
Chee,Y.L., & Watson,H.G. (2008). Aspirin and other antiplatelet drugs in the prevention of venous thromboembolism. Blood Reviews, 22(2), 107-116. doi:10.1016/j.blre.2007.11.001
Galson,S. (2008). Surgeon General’s Perspectives:Prevention of deep vein thrombosis and pulmonary embolism. Public Health Reports, 123, 420-421. Retrieved http://www.publichealthreports.org/
Lilliey, L. L., Harrington, S., & Snyder, J. S. (2007). Coagulation Modifier Drugs. In Pharmacology and the Nursing Process (pp. 417-439). Canada: Mosby, Inc.
Mueller, R. L. (2004). First-generation agents: aspirin, heparin. Best Practice & Research Clinical Haematology, 17(1), 23-53. doi:10.1016/j.beha.2004.03.003
this is very useful information & there are many helpful points in this info that I will pass on to my father. Is there a certain age in which one should start the preventative measure of taking an aspirin a day?
ReplyDelete-Kristina
what is meant by the risk of a bleeding episode can be associated w/ the frequent ingestion of an anticoagulant?
ReplyDelete-Paige
this is very informative, but I do have one question:
ReplyDeleteif surgery of some type is needed, what are the associated risks one may face when they have been taking an anticoagulant?
This was very informative information
ReplyDeleteThis is all very good to know. Definitely something people should take with them when thinking about both current and long term personal health care.
ReplyDelete-Christine
A common side effect of anticoagulants is bleeding. A bleeding episode could include anything from unusual bruising, bleeding gums while brushing your teeth, nosebleeds, heavy menstrual bleeding, blood in the urine to more severe internal bleeding or hemorrhage.
ReplyDeleteTadalafil 60 mg contains an active ingredient, this is a prescription based drug. Helps to treat the issue of erectile dysfunction from the roots of men. Tadalista 60 mg relaxes the muscles in the penis and increases blood flow to it, also used to treat the signs and symptoms of benign prostatic hyperplasia in adult males. The store is used to sell the best medicines at affordable prices.
ReplyDelete