Anticoagulant drugs

Question 1

What are the two main indications for anticoagulant drugs?

Answer 1

VTE

Atrial fibrillation

Question 2

What are the three different types of anticoagulant drugs?

Answer 2

• Heparin
• Coumarin anticoag. e.g. warfarin
• New anticoagulants - directly inhibit thrombin or factor Xa

Question 3

Heparin:

• how does it work?
• how is it delivered?
• what are the two different types?

Answer 3

• Potentiates antithrombin III
• given parenterally (IV or SC)

2 forms:

• unfractionated, usually antithrombinIII:thrombin potentiated (old type, small therapeutic window)
• LMWH, usually antithrombinIII:factor Xa potentiated (needs less monitoring)

Question 4

When is heparin used?

Answer 4

• in an acute thrombotic event

- short term use after surgery

Question 5

How is unfractionated heparin monitored?

Answer 5

APTT

• affects intrinsic pathway more than extrinsic
• both pathways affected at high dose

Question 6

How is LMW heparin monitored?

Answer 6

Can do a antiXa assay for LMWH but usually none required

Question 7

What are 3 main complications of heparin?

Answer 7

Bleeding

Heparin induced thrombocytopenia with thrombosis (HITT)

• Ab is made to platelets and binds to platelets = platelets stick together and can lead to life threatening thrombosis
• if pt. on heparin and platelet count drops = stop heparin

Osteoporosis:
-with long term use (only use short term)

Question 8

How can heparin be reversed?

Answer 8

Stop heparin: short T1/2 (longer with LMWH)

Protamine sulphate for severe bleeding is occasionally used (complete reversal for unfractionated/partial for LMWH)

Question 9

How do coumarin drugs work (warfarin)? when is this used?

Answer 9

inhibit vitamin K

used as long term anticoag. for those with a previous event or AF

Question 10

describe the four stages of therapy for warfarin?

Answer 10

Initiation:

• rapid, give high loading dose of heparin if pt had acute thrombosis
• slow, give low loading does if in community

Stabilisation:
-ideally pt should be stabilised prior to referral to community services

Maintenance:
-dose should be taken at the same time every day (6pm recommended)

Monitoring:
-narrow therapeutic window, aim for INR = 2.5 but if having further events INR = 3.5-5

Question 11

What is INR?

Answer 11

international normalised ratio

= (patient PT in seconds / mean normal PT)^ISI

Question 12

What 4 risk factors exist for major haemorrhage on warfarin?

Answer 12

• intensity of coagulation
• concomitant disease
• concomitant use of other drugs
• quality of management

Question 13

What degree of bleeding is normal on warfarin?

Answer 13

-skin bruising
-epistaxis
-haematuria
(mild)

Question 14

What degree of bleeding is worrying on warfarin?

Answer 14

• GI bleed
• intracerebral
• significant drop in Hb

Question 15

What are the 4 different options to manage bleeding on warfarin? what determines which option is used?

Answer 15

1 - no action

2 - omit warfarin dose: takes several days

3 - administer oral vit K: takes 6 hours for effect (oral or IV)

4 - administer clotting factors: FFP or factor concentrates = immediate affects (emergency or lifethreatening situation)

Assess: clinical or lab assessment of response

Management of bleeding is dependant on bleeding severity/INR/Speed action

Question 16

what are the pros and cons of new oral anticoag.?

Answer 16

Pros:

• oral
• no monitoring required
• less drug interactions

Cons:

• expensive
• no antedote for reversal
• unlicensed in pregnancy

Question 17

What is the name of the direct thrombin inhibitor? what is the main complication of this drug?

Answer 17

Dibigatran

-excreted in kidney and can cause accumalation and kidney failure

Question 18

What are the names of the 2 direct factor Xa inhibitors?

Answer 18

Rivaroxiban

Apixaban

Question 19

When are NOAC drugs used?

Answer 19

• instead of LMWH as prophylaxis in elective knee and hip surgery
• used for selective patients in stroke prevention for AF
• used for treatment of DVT/PE