Pharmacology can be a daunting topic for both EMS and nursing alike. This week's blog will center on the cardiovascular system while we help you make more sense of antiplatelets and anticoagulants -- their mechanisms around clot inhibition are NOT the same.
Anti-platelets- (ASA, Brilinta and Plavix)
These drugs work specifically on primary hemostasis whose action is centered on the formation of an unstable and temporary platelet plug. As the name suggests, anti-platelets slow down or inhibit platelet aggregation or "stickiness". When platelets are activated, they release chemicals, which trigger more platelets to arrive and aggregate at the scene of the crime. These drugs work on the arterial system and primarily focus on clot prophylaxis or prevention. You want to prevent new ischemic events, or new in-stent thrombosis. For stable angina - you may be prescribed these medications for up to 6 months. For unstable angina/stent placement for STEMI/NSTEMI you may be on these drugs for a year or longer based on current guidelines. This class of medications are commonly given for peripheral artery disease and strokes as well.
Anticoagulants- (Heparin, Coumadin, Pradaxa, Eliquis, and Xarelto)
These drugs work specifically on secondary hemostasis, whose action is centered on activation of several clotting proteins/factors with the end goal of stable fibrin clot formation. This stabilizes the earlier work done by the platelets in primary hemostasis. These medicines play a role in prevention of new clots as well, but they also prevent the growth of existing clots. The above drugs work by inhibiting various clotting factors. For example, Heparin makes antithrombin work better while slowing down factor Xa. Newer oral anticoagulants like Eliquis and Xarelto also inhibit Xa. Coumadin inhibits factor VII. Pradaxa inhibits factor II.
These drugs work on the venous system. This class of medications are commonly given for deep venous thrombosis (DVT's), pulmonary embolism and chronic atrial fibrillation.
Thrombolytics- (tPA, Alteplase, and Tenecteplase)
These drugs are the ONLY ones that truly dissolve existing clots and so they are termed clot busters. These come with bleeding risks, but sometimes the benefits can outweigh these risks. These are never given to patients who have active bleeding, a recent surgery or marked hypertension. In rural environments you may see these given to STEMI patients who cannot get to a cath lab in a timely fashion. More commonly, you will see bolus and then infusions given to ischemic stroke patients who have elevated NIH scores... new data even suggests given this drug if certain criteria are met even when the NIH scores are lower. Keep in mind in cases of large vessel occlusions these drugs alone may not be enough and further neurosurgery interventions will be likely.
Antifibrinolytics- (TXA)
When clot get formed, they must also be broken down and dissolved. Primary fibrinolysis is a normal body function that acts like a vacuum cleaner dissolving clots after they have completed their job. Blood flow is restored, and everything is cleaned up. We have to clean up once the party is over because even too much fibrin clot can be a bad thing. The clot grows, and by doing so it can occlude vessels amongst other things. However, in times of significant and acute blunt or penetrating trauma with associated bleeding and hemodynamic instability, it may be necessary to halt the normal fibrinolytic process. Keep in mind that TXA does NOT promote clotting, but instead prevents fibrin breakdown. This allows the clots to remain active and hopefully stop or reduce the bleeding process. 1000 mg (in 100ml NSS) is usually given in a dedicated IV line over the course of 10 mins or so. The drug has been around for decades, it faired really well in military/tactical environments and is now commonly used in both the pre-hospital and hospital settings.
A wise gentleman once said there are only 2 ways to coagulate, but MANY ways to bleed. Life threatening hemorrhage is not always tied to traumatic injuries, so keep medical causes of bleeding in mind as part of your differential diagnosis. Consider combating the high mortality/morbidity of this patient population with comprehensive whole blood programs. As you may be keenly aware, successful and sustainable programs are being setup all over the country. This is a good thing!! Good luck on your next Pharmacology review -- hopefully this short blog was beneficial and complimented your learning.
September 9, 2024
Author: Joshua Ishmael, MBA, MLS(ASCP)CM, NRP
Pass with PASS, LLC
Comments