Anticoagulants Flashcards
(20 cards)
What are anticoagulants and what type of thrombus are they more useful for?
Anticoagulants are drugs that prevent or reduce blood clots by inhibiting factors of the coagulation cascade. They are more useful for venous thrombus.
How does heparin work as an anticoagulant?
Heparin binds and activates antithrombin, enhancing its activity by 1000-fold, which then inhibits the enzymes factor IIa (thrombin) and factor Xa.
What is the composition of heparin and how is it administered?
Heparin is made of a mixture of glycosaminoglycans (polymers) and is administered intravenously or subcutaneously.
What is the main unwanted effect of heparin and how is it monitored?
The main unwanted effect is haemorrhage. It is monitored using activated partial thromboplastin time (aPTT).
What is heparin-induced thrombocytopenia (HIT)?
HIT is an immune-mediated reaction where antibodies activate platelets in the presence of heparin, leading to thrombosis.
What is unfractionated heparin (UFH) and what factors does it inhibit?
UFH is a mixture of glycosaminoglycans that binds to antithrombin and inhibits factors IIa and Xa.
How does low molecular weight heparin (LMWH) differ from UFH?
LMWH has a shorter polymer chain, lacks the long chain to bind thrombin effectively, and primarily inhibits factor Xa, with minimal anti-IIa activity.
What are the advantages of ultra-low molecular weight heparin (ULMWH)?
ULMWH allows for less frequent dosing (1–2 times daily), has more predictable effects, does not require monitoring, and has a lower risk of HIT.
What is the source of hirudins and how do they work?
Hirudins are derived from leech saliva and act as direct thrombin inhibitors. An example drug is bivalirudin.
What does activated partial thromboplastin time (aPTT) measure?
aPTT measures the time it takes for blood to clot when the intrinsic pathway is activated.
What is warfarin and how does it work?
Warfarin is a vitamin K antagonist that inhibits vitamin K epoxide reductase, preventing vitamin K recycling needed for activating clotting factors II, VII, IX, and X.
What are some advantages and disadvantages of warfarin?
Advantages: Long-established, once-daily oral, safe in renal impairment, and has reversal agents like vitamin K and prothrombin complex.
Disadvantages: Takes days to reach a therapeutic level, has many drug and food interactions, a narrow therapeutic window, and requires frequent monitoring (e.g., PT/INR).
What is the purpose of monitoring INR in warfarin therapy?
INR is used to adjust warfarin dosage to maintain a therapeutic level, ideally between 2 and 3.
How do DOACs differ in mechanism from warfarin?
DOACs directly and specifically inhibit a single clotting factor (e.g., IIa or Xa) rather than interfering with the metabolism of several factors as warfarin does.
Give examples of DOACs and the factors they inhibit.
Dabigatran inhibits thrombin (factor IIa), while rivaroxaban, apixaban, and edoxaban inhibit factor Xa.
What are the advantages of DOACs over warfarin?
DOACs offer specific inhibition, rapid onset, fixed dosing with no need for monitoring, fewer interactions, and a better safety profile.
What are some disadvantages of DOACs compared to warfarin?
Higher cost, bleeding risk still exists, and they may not be suitable for patients with renal impairment.
Why does low molecular weight heparin (LMWH) primarily inhibit factor Xa rather than thrombin?
LMWH is a shorter polymer and lacks the longer chain required to bind thrombin effectively, so it mainly inhibits factor Xa, with only minimal anti-IIa activity.
Why is monitoring not typically required for patients on DOACs?
DOACs have predictable pharmacological effects, allowing for fixed dosing, which eliminates the need for routine monitoring unlike warfarin.
How does the presence of food rich in vitamin K affect warfarin therapy?
Foods high in vitamin K can interfere with warfarin’s effect by promoting clotting factor activation, leading to reduced anticoagulant efficacy and potential treatment failure.
