Anticoagulant therapy

Question 1

main use of anticoagulants

Answer 1

prevent thrombus formation or extension of an existing thrombus in the slower-moving venous side of the circulation, where the thrombus consists of a fibrin web enmeshed with platelets and red cell

Anticoagulants are of less use in preventing thrombus formation in arteries, for in faster-flowing vessels thrombi are composed mainly of platelets with little fibrin

Question 2

Direct-acting oral anticoagulants (DOACs)

Answer 2

Apixaban, edoxaban, and rivaroxaban are reversible inhibitors of activated factor X (factor Xa) which prevents thrombin generation and thrombus development

Question 3

Dabigatran etexilate

Answer 3

reversible inhibitor of free thrombin, fibrin-bound thrombin, and thrombin-induced platelet aggregation.

Question 4

DOAC main use

Answer 4

• prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation
• tx and secondary prevention of dvt/pe

Question 5

DOAC monitoring

Answer 5

Routine anticoagulant monitoring is not required

Question 6

INR

Answer 6

INR is a measure of how long it takes blood to clot. In healthy people an INR of 1 is normal.

Question 7

Warfarin

Answer 7

vitamin K antagonists
inhibiting vitamin K dependent clotting factors (II, VII, IX, X) in addition to the anticoagulant proteins C and S

Question 8

main side effect of warfarin

Answer 8

involves bleeding more easily than normal (e.g. epistaxis, bleeding gums, heavier periods, bruising)

commonly occur in the first few weeks of treatment or when the patient is unwell.

Question 9

Common side effects (other than bleeding) of warfarin include:

Answer 9

a mild rash
hair loss

Question 10

Serious side effects of warfarin can include:

Answer 10

jaundice
skin necrosis

Question 11

Warfarin counselling points

Answer 11

“It is normal to bleed more easily when taking warfarin as the medication works by thinning the blood. Common types of bleeding include:

• periods
• if cut self will bleed longer
• occasional nosebleed
• bleeding gums
• brusises

safety net against serious bleeding

Question 12

Intrinsic pathway

Answer 12

The intrinsic pathway is activated by contact with a damaged surface and =:

Factor XII → Factor XI → Factor IX (+ Factor VIII + vWF) → Common pathway

Question 13

Extrinsic pathway

Answer 13

The extrinsic pathway is activated by the release of tissue factors and goes as follows:

Factor VII → Common pathway

Question 14

prothrombin time (PT)

Answer 14

measure of the time taken for blood to clot via the extrinsic pathway
INR is a standardised version of this test
these tests are a measure of overall clotting factor synthesis or consumption.

Question 15

activated partial thromboplastin time (APTT)

Answer 15

measure of the time taken for blood to clot via the intrinsic pathway

Question 16

Heparin MOA

Answer 16

Heparins bind to antithrombin (AT) and induce a conformational change that makes AT an efficient inactivator of coagulation factors in mainly the intrinsic pathway

Question 17

Thrombin time

Answer 17

how fast fibrinogen is converted to fibrin by thrombin.

Question 18

Major bleeding on warfarin Mx

Answer 18

1.stop warfarin
2. give phytomenadione (vitamin K1) IV
3. give dried prothrombin complex or FFP if not available

Question 19

INR >8.0, minor bleeding Mx

Answer 19

1. stop warfarin
2. give phytomenadione (vitamin K1) IV, repeat dose of phytomenadione if INR still too high after 24 hours
3. restart warfarin sodium when INR <5.0

Question 20

INR >8.0, no bleeding Mx

Answer 20

1. stop warfarin
2. give phytomenadione (vitamin K1) po, repeat dose of phytomenadione if INR still too high after 24 hours
3. restart warfarin when INR <5.0

Question 21

INR 5.0–8.0, minor bleeding Mx

Answer 21

1. stop warfarin
2. give phytomenadione (vitamin K1) IV
3. restart warfarin sodium when INR <5.0