Anticoagulant Drugs

Question 1

State the 2 main indications for anticoagulant drugs

Answer 1

• Atrial fibrillation
• Venous thrombosis (treatment & prophylaxis)
  - DVT/PE, surgery, APS, prosthetic valve etc

Question 2

What are anticoagulant drugs

Answer 2

Drugs that target & prevent the formation of a fibrin clot.
I.e. are secondary haemostasis inhibitors

Question 3

Name the three main anticoagulant drugs

Answer 3

Warfarin
Heparin
DOACs

Question 4

Name two conditions where warfarin is recommended over DOACs

Answer 4

• APS
• Prosthetic heart valves

Question 5

Heparin MOA. Does this have a delayed or immediate effect?

Answer 5

Potentiates antithrombin (immediate effect)

Question 6

State the two forms of heparin and compare the effect they have

Answer 6

Unfractioned heparin - Tend to react more to thrombin
Low molecular weight heparin - Tend to react more to VIII/Xa

Question 7

How do you monitor unfractioned heparin

Answer 7

APTT

(Prolongs both APTT & PT but APTT is more sensitive)

Question 8

How do you monitor LMWH

Answer 8

Not usually a need for monitoring
Xa effect is more predictable than thrombin

Question 9

How can heparin affect platelet count

Answer 9

• Heparin-induced thrombocytopenia (with thrombosis)
• Immune reaction to heparin leading to platelets ‘clumping’ together
• Must monitor FBC in patients on heparin

Question 10

Heparin side effects

Answer 10

• Bleeding
• Heparin induced thrombocytopenia (with thrombosis)
• Osteoporosis (chronic use)

Question 11

What is a benefit of heparin, particularly unfractioned heparin

Answer 11

• It has a really short half life
• Protamine sulphate can completely reverse unfractioned heparin & partially reverse LMWH

Question 12

What are the two heparin formulation options

Answer 12

IV or SC

Question 13

What type of drug is warfarin, name 3 other drugs in the same drug class

Answer 13

Coumarin anticoagulant
Other examples: Phenindione, acenocoumarin, phenoprocoumon

Question 14

Warfarin MOA

Answer 14

• 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)

Question 15

Why are people starting warfarin also started with LMWH? Why can’t warfarin be used in acute situation?

Answer 15

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)

Question 16

What test is most sensitive to warfarin and what is the results used to calculate

Answer 16

Prothrombin time (warfarin effect on VII)
Used to calculate INR

Question 17

What is INR & what does it indicate

Answer 17

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

Question 18

What is the major side effect of warfarin and what can increase the risk of an individual being affected

Answer 18

Bleeding/haemorrhage

• Certain drug interactions/ diseases/ binge drinking
• Quality & intensity of management

Question 19

How can you reverse warfarin in a patient who is bleeding

Answer 19

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)

Question 20

Warfarin formulation

Answer 20

Oral, same time every day

Question 21

DOAC MOA

Answer 21

Direct thrombin inhibitors (Dabigatran)
Direct activated factor X inhibitors (apixaban, rivaroxaban)

Question 22

DOAC indications

Answer 22

• Instead of LMWH as prophylaxis in hip & knee replacement
• DVT/PE treatment
• Stroke prevention in A Fib patients

Question 23

DOAC benefits

Answer 23

• Oral
• No monitoring (predictable response)
• Less drug interactions, can binge drink on them

Question 24

Unfractioned vs LMWH

Answer 24

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

LMWH
- Has a longer duration of action
- Can be administered subcutaneously
- & so is used more routinely than UFH

Question 25

Why is APTT used instead of PT in heparin monitoring

Answer 25

APTT is sensitive to all the coagulation factors that heparin targets, whereas PT is not

Question 26

Why is PT used instead of APTT in warfarin monitoring

Answer 26

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