Anticoagulant Drugs Flashcards
State the 2 main indications for anticoagulant drugs
- Atrial fibrillation
- Venous thrombosis (treatment & prophylaxis)
- DVT/PE, surgery, APS, prosthetic valve etc
What are anticoagulant drugs
Drugs that target & prevent the formation of a fibrin clot.
I.e. are secondary haemostasis inhibitors
Name the three main anticoagulant drugs
Warfarin
Heparin
DOACs
Name two conditions where warfarin is recommended over DOACs
- APS
- Prosthetic heart valves
Heparin MOA. Does this have a delayed or immediate effect?
Potentiates antithrombin (immediate effect)
State the two forms of heparin and compare the effect they have
Unfractioned heparin - Tend to react more to thrombin
Low molecular weight heparin - Tend to react more to VIII/Xa
How do you monitor unfractioned heparin
APTT
(Prolongs both APTT & PT but APTT is more sensitive)
How do you monitor LMWH
Not usually a need for monitoring
Xa effect is more predictable than thrombin
How can heparin affect platelet count
- Heparin-induced thrombocytopenia (with thrombosis)
- Immune reaction to heparin leading to platelets ‘clumping’ together
- Must monitor FBC in patients on heparin
Heparin side effects
- Bleeding
- Heparin induced thrombocytopenia (with thrombosis)
- Osteoporosis (chronic use)
What is a benefit of heparin, particularly unfractioned heparin
- It has a really short half life
- Protamine sulphate can completely reverse unfractioned heparin & partially reverse LMWH
What are the two heparin formulation options
IV or SC
What type of drug is warfarin, name 3 other drugs in the same drug class
Coumarin anticoagulant
Other examples: Phenindione, acenocoumarin, phenoprocoumon
Warfarin MOA
- Inhibits vitamin K
- This prevents vitamin K from carboxylating factor II, VII, IX, X as well as protein C & S
- This prevents the coagulation factors binding to platelets (creating non-functional coagulation factors)
Why are people starting warfarin also started with LMWH? Why can’t warfarin be used in acute situation?
Warfarin initially reduces functional protein C & S before it reduces clotting factors II, VII, IX, X. This increases the patients risk of thrombosis
Therefore, LMWH must be given at the start of treatment until warfarin starts affecting the clotting factors &
Warfarin can’t be used in acute situations as it takes ~1 week to work (affect the clotting factors)
What test is most sensitive to warfarin and what is the results used to calculate
Prothrombin time (warfarin effect on VII)
Used to calculate INR
What is INR & what does it indicate
INR is ratio of the patients prothrombin time: normal reference range prothrombin time
If it is low (prolonged PT) - patient is at risk of a blood clot
If it is high (quick PT) - patient is a t risk if a bleed
What is the major side effect of warfarin and what can increase the risk of an individual being affected
Bleeding/haemorrhage
- Certain drug interactions/ diseases/ binge drinking
- Quality & intensity of management
How can you reverse warfarin in a patient who is bleeding
Multiple options, depends on bleeding severity
- omit warfarin dose (works in 3 days)
- oral vitamin K (works in 6 hours)
- oral clotting factors (works immediately) (transfusion risks)
Warfarin formulation
Oral, same time every day
DOAC MOA
Direct thrombin inhibitors (Dabigatran)
Direct activated factor X inhibitors (apixaban, rivaroxaban)
DOAC indications
- Instead of LMWH as prophylaxis in hip & knee replacement
- DVT/PE treatment
- Stroke prevention in A Fib patients
DOAC benefits
- Oral
- No monitoring (predictable response)
- Less drug interactions, can binge drink on them
Unfractioned vs LMWH
UFH
- Has a short duration of action
- Is administered intravenously (IV).
- Its effects can be quickly reversed by stopping the infusion.
- & so it is used in patients at risk of bleeding
- & is also used in patients with kidney disease
LMWH
- Has a longer duration of action
- Can be administered subcutaneously
- & so is used more routinely than UFH
Why is APTT used instead of PT in heparin monitoring
APTT is sensitive to all the coagulation factors that heparin targets, whereas PT is not
Why is PT used instead of APTT in warfarin monitoring
Factor VII has the shortest half life & is reduced first in response to warfarin (compared to II, IX, X) which will be reflected as a prolonged PT
