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Haematology > Anticoagulant Drugs > Flashcards

Anticoagulant Drugs Flashcards

1
Q

What are some indications for prescribing anticoagulant drugs?

A

Atrial fibrillation and venous thrombosis

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2
Q

What part of the haemostatic mechanism do anticoagulant drugs target?

A

The fibrin clot (secondary haemostasis)

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3
Q

Why does atrial fibrillation predispose to thrombosis?

A

Causes stasis of blood in the left atrium as the heart doesn’t pump properly

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4
Q

What is the action of heparin?

A

Potentiates antithrombin = has immediate effect

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5
Q

How is heparin given?

A

Parenteral = IV or SC

2 forms = unfractionated, low molecular weight

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6
Q

What is the action of LMWH?

A

Keeps thrombin/factor Xa complex together = more predictable action so can use fixed dose

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7
Q

What is the action of unfractionated heparin?

A

Binds to thrombin/anti-thrombin complex to keep it together

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8
Q

How is unfractionated heparin monitored?

A

Using the activated partial thromboplastin time

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9
Q

How is LMWH monitored?

A

Anti-Xa assay can be used = only done in complicated patients (e.g renal failure)

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10
Q

What effect does heparin have on the prothrombin and activated partial thromboplastin times?

A

Prolongs both

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11
Q

What are the complications of heparin?

A

Bleeding, heparin induced thrombocytopenia (monitor FBC), osteoporosis if long term

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12
Q

How is heparin reversed?

A

Stop heparin = short half life if unfractionated

Protamine sulphate in severe bleeding = reverses anti-thrombin effect

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13
Q

How effective is protamine sulphate at reversing heparin?

A

Completely reverses unfractionated heparin

Partially reverses LMWH

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14
Q

What are some examples of coumarin antagonists?

A

Warfarin, phenindone, acenocoumarin

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15
Q

What is the action of coumarin anatagonists?

A

Inhibit vitamin K = causes production of inactive clotting factors

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16
Q

What elements of the haemostatic mechanism are dependent on vitamin K?

A

Factors II, VII, IX and X

Proteins C and S

17
Q

Why is warfarin prescribed alongside warfarin for the first 3-5 days?

A

Protein C and S levels fall before clotting factors do = causes transient increases in clot risk

18
Q

Why is warfarin monitored?

A

It has a narrow therapeutic index = aim of INR of 2-3

19
Q

How should warfarin be taken?

A

Can be started slowly or rapidly = takes 6hrs to work

Dose should be taken at same time every day

20
Q

How does warfarin affect the prothrombin and activated partial thromboplastin times?

A

Prothrombin time more sensitive to warfarin so is prolonged by more

21
Q

What is the INR?

A

Mathematical correction for differences in the sensitivity of thromboplastin reagents

22
Q

What does the INR allow for?

A

Comparison of results between labs and standardises reporting of prothrombin time

23
Q

What are the factors that influence bleeding risk with warfarin use?

A

Intensity of anticoagulation
Concomitant clinical disorders and use of other medications = beware of drug interactions
Quality of management

24
Q

What are some bleeding complications that occur with warfarin use?

A 
Mild = skin bruising, epistaxis, haematuria
Severe = GI or intra-cerebral, significant drop in Hb
25
Q

How is warfarin reversed?

A

No action = minor bleeding with INR in range
Omit dose = high INR but minor bleed
Oral vitamin K = INR >8
Factor concentrates = life threatening bleed

26
Q

What are the new oral anticoagulants?

A

Direct thrombin inhibitors = dabigatran

Oral Xa inhibitors (more common) = rivaroxaban, epixaban

27
Q

What are the benefits of newer oral anticoagulants?

A

Don’t require close monitoring

Less drug interactions

28
Q

Why may direct thrombin inhibitors not be useful in the elderly?

A

They are renally excreted

29
Q

What are the uses of newer oral anticoagulants?

A

In place of heparin as prophylaxis in elective hip/knee replacement surgery
DVT/PE treatment
Stroke prevention in atrial fibrillation

Haematology (24 decks)

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