8.1: Antiplatelet And Anticoagulant Therapy

Question 1

How does warfarin work?

Answer 1

Inhibits the production of vitamin K dependent clotting factors 2, 7, 9, 10

Question 2

What would a patient with previous Hx of DVT/ PE/ AF who is on warfarin, aim for an INR range between?

Answer 2

2 to 3

DVT = on warfarin for 3 to 6 months
PE = on warfarin for 6 months
AF = on warfarin until risk > benefits

Question 3

What are some adverse effects of warfarin?

Answer 3

Teratogenic

Bleeding (epistaxis, intracranial haemorrhage, GI bleeding-> anaemia)

Question 4

What is Virchow’s triad?

Answer 4

Abnormal constituents of blood eg on OCP, smoker, malignancy
Abnormal flow
Abnormalities in vessel walls

Question 5

Why does heparin need to be given initially to a patient commencing warfarin therapy?

Answer 5

Due to its slow onset of action, due to turnover of clotting factors

Question 6

How long before surgery does warfarin need to be stopped?

Answer 6

3 days

Due to its slow onset of action, half life approx 48 hours

Question 7

How can warfarin be monitored in patients?

Answer 7

PT time
INR
Extrinsic pathway factors

Question 8

What are some drugs that can potentiate warfarin?

Will they increase or decrease the INR?

Answer 8

Alcohol, aspirin, NSAIDs, amiodarone, metronidazole, quinolone, cephalosporin abx

Increase INR

Question 9

What are some drugs that will inhibit warfarin?

Will they increase or decrease the INR?

Answer 9

Antiepileptics, except Na valproate
Rifampicin
St Jons Wort

They will decrease the INR

Question 10

How can warfarin therapy be reversed, eg in a px with major bleed?

Answer 10

Stop warfarin (don’t restart until INR <5)
IV vitamin K (slow)
Fresh frozen plasma (fast)

Question 11

Which factor do heparins activate?

Answer 11

Anti thrombin 3 (to inactivate Xa)

UF heparin can also inactivate thrombin (as it as a longer chain to can bind to both molecules, unlike LMWH)
LMWH affect Xa specifically

Question 12

How are the types of heparin given?

Answer 12

Heparin must be given parentally due to poor GI absorption

UF heparin given IV
LMWH given SC

Question 13

What are some adverse effects of heparin?

Answer 13

Bruising and bleeding
Thrombocytopenia
Osteoporosis

Question 14

Why is LMWH more favourably?

Answer 14

Does not require monitoring unless UFH

Question 15

How can heparin be reversed if a px is bleeding?

Answer 15

Stop heparin

Give protamine

Question 16

What type of drugs are apixaban and rivaroxaban?

Answer 16

DOACs

Question 17

What types of drugs are enpxaparin and dalteparin?

Answer 17

LMWH

Question 18

What scoring system can be used to decide whether to commence a patient on an anticoagulant by assessing their stroke risk?

Answer 18

CHA2DS2VASc

Treat anyone with a score of 2 or more with anticoagulants

Question 19

How does aspirin work?

Answer 19

Via COX1 inhibition

Question 20

Why can the fibrinolytic drug streptokinase only be used once?

Answer 20

As it’s a bacterial protein so it antigenic

So the body generated blocking antibodies to it which persist for many years