Chapter 27- anticoagulants, antiplatelets, thrombolytics Flashcards
What are the two pathways that lead to coagulation?
intrinsic pathway- activated in response to injury
extrinsic pathway- activated when when blood leaks out of a vessel and enters tissue spaces
Steps that initiate the clotting process
- when blood vessel is injured, vessel spasms and constricts (limits blood flow to injured area)
- platelets become sticky, adhering to each other and to damaged vessel
- as the bound platelets break down, they release substances that attract more platelets to the area…the flow of blood is reduced, thus allowing the process of COAGULATION
coagulation cascade
- coagulation occurs when fibrin threads create a meshwork that traps blood constituents so that they develop a CLOT
- two separate pathways lead to coagulation…
- intrinsic pathway
- extrinsic pathway
- near end of cascade, a chemical called prothrombin activator—> prothrombin—-> thrombin—>fibrinogen—>fibrin
- these fibrin strands provide framework for the clot
REMOVAL of blood clots
- called FIBRINOLYSIS
- initiated within 24-48 hours of clot formation and continues until clot is dissolved
What are the several steps of fibrinolysis?
- when fibrin clot is formed, nearby blood vessels secret enzyme TISSUE PLASMINOGEN ACTIVATOR (TPA)—>plasminogen—> plasmin—>digests fibrin strands and removes clot
- the body regulates fibrinolysis so that UNWANTED fibrin clots are are removed; fibrin present in wounds is left to maintain hemostasis
thromboembolic disorders occur when…
- the body forms undesirable clots
- a stationary clot is called a THROMBUS (if in a vessel, it grows larger as more fibrin is added)
- traveling clot is called an embolus
bleeding disorders are characterized by…
- abnormal clot formation
- thrombocytopenia- most common bleeding disorder and is a deficiency of platelets
- hemophilias-bleeding disorder caused by genetic deficiencies in specific clotting factors
what is the most common inherited bleeding disease?
von Williebrand’s disease (vWD)
-results in decrease in quantity or quality of von Williebrand factor, which has a role in platelet aggregation
mechanisms of coagulation modification
- prevention of the formation of clots= ANTICOAGULANTS, ANTIPLATELETS
- dissolve clots, removal of existing clot= THROMBOLYTICS
- promote formation of clots= HEMOSTATICS
3 examples of anticoagulants
warfarin (Coumadin)
heparin
enoxaparin (Levonox)
heparin’s action
- prevents conversion of prothrombin to thrombin and the conversion of fibrinogen to fibrin
- binds to antithrombin III (which inactivates thrombin)
- inactivates several clotting factors
action of warfarin
- interferes with the vitamin K dependent factors by reducing synthesis of vitamin K
- inhibits hepatic synthesis of coagulation factors
Specific points of Coumadin (what does it treat, what route of administration, pregnancy?)
- treatment of atrial fib, CHF, valvular disease, pulmonary embolus, deep vein thrombosis (DVT)
- takes 3-5 days for therapeutic dose
- ORAL (long term treatment)
DO NOT TAKE while pregnant
Coumadin (antidote, how to monitor effectiveness)
-antidote= VITAMIN K
MONITOR PT
- how to monitor effectiveness?
1. 5 to 2 x baseline= therapeutic range
example: normal PT is 2.0-3.0
Heparin (route of administration, antidote, pregnancy?)
route of admin= IV and subcutaneous
- antidote= PROTAMINE SULFATE
- heparin CAN be used with pregnancy, warfarin CANNOT
Heparin (monitor effectiveness, other facts)
-quick onset
-indirect thrombin inhibitor
-how to monitor effectiveness?
1.5 to 2.5 x baseline= therapeutic range
MONITOR PTT
example: normal PTT is 25
so, 25x1.5=37.5 and 25x2.5=62.5
someone taking heparin should have PTT of 37.5-62.5
Enoxaparin (monitor effectivess, antidote, route of administration)
- monitor effectiveness: do not really test effectiveness; PTT levels would probably go up, so you could monitor that
- antidote= protamine sulfate? (b/c cousin to heparin)
- route of administration= subcutaneous in abdomen (about 2-3 inches away from umbilicus)
enoxaparin (facts)
- same as heparin except has a longer half life
- lower molecular weight, doesn’t bind with proteins
antiplatelet medications
-interferes with platelet aggregation
-affects ADP and TXA2
PLAVIX
common antiplatelet medications
- aspirin
- ticlopidine (Ticlid)
- clopidogrel (Plavix)
When are IV antiplatelets usually given? What is the half life of antiplatelet drugs?
- IV antiplatelets can be used before a diagnosis (such as MI) is confirmed; patient needs meds immediately so IV antiplatelets may be given (until diagnosis confirmed)
- half life of antiplatelet medications is the half life of the platelet! (so about 5 days; platelets live about 10 days)
what are therapeutic uses of antiplatelet drugs?
- preventing clot formation
- mainly for the disease processes of heart attack, strokes
- antiplatelets are used second to treat DVT when patient cannot take anticoagulants
contraindications of anticoagulants
- active bleeding
- head injury
- recent surgery
- bleeding disorder
- advanced liver and renal disease
- postpartum
- pregnancy with warfarin (not with heparin)
drug interactions with anticoagulants
- any antiplatelet or antithrombotic medication
- spinal-epidural anesthesia
- food with high vitamin K content
- some herbs
- many drug interactions with warfarin
- ALCOHOL (alcohol will prolong bleeding)
