U2.3 Anticoagulants

Question 1

Describe Stage 1 of hemostasis.

Answer 1

Formation of a platelet plug.

• Platelet aggregation initiated by exposure to collagen.
• Formation of fibrinogn bridges betwen glycoprotein IIb/IIa receptors
• GP receptors must first be activated - stimulated by multiple factors (thromboxane, thrombin, collagen, platlet activating factor, ADP)
• Plug is unstable and must be reinforced by fibrin. (some drugs degrade fibrin)

Question 2

Describe Stage 2 of hemostasis.

Answer 2

Coagulation.

• Production of fibrin which stabilizes the clot.
• Production by two pathways - intrinsic & extrinsic
• Both pathways meet at Factor Xa

Question 3

Describe the intrinsic pathway of coagulation.

Answer 3

contact activation

• Turned on when blood makes contact with collagen as a result of trauma to a blood vessel.
• heparin affects this pathway

Question 4

Describe the extrinsic pathway of coagulation.

Answer 4

tissue factor

• Turned on when there is trauma to the vascular wall.
• Triggers release of tissue thromboplastin.
• Causes conversion of prothrombin to thrombin.
• Also causes a number of factors to be activated, as well as conversion of fibrinogen to fibrin.
• warfarin affects this pathway

Question 5

anticoagulants

Answer 5

Prevention of clot formation by inhibiting specific clotting factors.
e.g.: heparin, warfarin, lepirudin

Question 6

antiplatelets

Answer 6

Prevention of clot formation by inhibiting platelet actions.

e.g.: clopidogrel, abciximab

Question 7

thrombolytics

Answer 7

Removal of an existing clot, the drug dissolves the clot.

e.g.: alteplase

Question 8

hemostatics

Answer 8

Promotion of clot formation by inhibition of fibrin destruction.
e.g.: aminocaproic acid

Question 9

clotting factor concentrates

Answer 9

Promotion of clot formation by the administration of missing clotting factors.

Question 10

PT

Answer 10

prothrombin time = Time it takes for plasma to clot AFTER the addition of tissue factor.

• Measure of extrinsic pathway
• Measured in INR which a ratio based on patient’s time vs. a control
• Normal INR is 0.8 to 1.2 (apprx. 1:1)

Question 11

aPTT

Answer 11

partial thromboplastin time = Time it takes for plasma to clot, called partial due to absence of tissue factor.

• Measure of intrinsic pathway
• Normal is 30 to 50 seconds