Warfarin & anti-coagulants

Question 1

When is the ideal time to check INR and give warfarin?

Answer 1

INR checked at 9am and dose administered at 6pm

Question 2

What does the INR measure?

Answer 2

Value is derived from prothrombin time which measures the extrinsic pathway of coagulation

Question 3

What is a normal INR in the absence of anti-coagulation?

Answer 3

0.8-1.2

Question 4

What INR value gives a risk of bleeding?

Answer 4

INR>5

Question 5

What INR value gives a risk of clotting?

Answer 5

INR<0.5

Question 6

What is the target INR for warfarinised patients?

Answer 6

2.5

Question 7

What is the half life of warfarin?

Answer 7

35-40 hours, thus is taken once daily

Question 8

What agent is used to reverse the effects of warfarin?

Answer 8

Vitamin K

Question 9

Can warfarin be used in pregnancy? Are there alternatives?

Answer 9

Contraindicated in pregnancy

Heparin is safe to use in pregnancy and while breastfeeding

Question 10

What are some medications that should be avoided whilst taking warfarin?

Answer 10

Aspirin, tramadol and NSAIDs can increase the risk of bleeding

Question 11

What checks should be done prior to commencing warfarin?

Answer 11

Drug history, allergies, LFTs, renal function and thyroid function

Question 12

How long does warfarin take to reach maximum effect?

Answer 12

5-10 days

Question 13

When is rapid loading of warfarin done?

Answer 13

To treat PE, DVT or mechanical prosthetic cardiac valve insertion

Question 14

What is given with warfarin during rapid loading?

Answer 14

LMWH is started to provide anticoagulant cover during rapid loading, continuing until the INR is within therapeutic range for 2 consecutive days

Question 15

What dose of warfarin is given when rapid loading?

Answer 15

10mg initially then tapered according to INR

Question 16

When is slow loading of warfarin done?

Answer 16

In non-acute settings e.g. AF where immediate anticoagulation is not required and the INR can be stabilised within 3-4 weeks

Question 17

What dose is warfarin started in patients in non-acute settings?

Answer 17

1-3mg daily then the INR checked weekly until stable

The daily dose is increased once per week by 1mg per day until INR reached 2.5

Question 18

Name some direct Xa inhibitors

Answer 18

Apixaban, rivaroxaban, edoxaban

Question 19

Name some direct thrombin inhibitors

Answer 19

Dabigatran, etexilate

Question 20

What is the preferred injectable/parenteral anticoagulant and why?

Answer 20

LMWH is preferred to unfractionated heparin due to the lower risk of HIT

Question 21

What tests should be done prior to starting LMWH?

Answer 21

INR, APTT, platelets and LFTs

Question 22

How is stroke managed if they present within 4.5 hours?

Answer 22

Thrombolysis with IV alteplase

CT scan must be done prior to this to rule out haemorrhage

Question 23

How is stroke managed after initial therapy?

Answer 23

300mg aspirin should be started daily for 2 weeks within 24 hours of thrombolysis or within 48 hours of symptom onset
After these 2 weeks, switch to clopidogrel 75mg daily