Warfarin

Warfarin

Question 1. Name Three Antiplatelet Agents.
Answer:

The following are three antiplatelet agents:

• Aspirin
• Dipyridamole
• Clopidogrel.

Question 2. Classify And Enumerate Anticoagulants.
Answer:

Classifiation and Enumeration of Anticoagulants

1. Used in Vivo

• Parenteral anticoagulant:
  • Indirect thrombin inhibitors: Heparin (unfractionated), low molecular weight heparins (enoxaparin, reviparin, nadroparin, dalteparin, parnaparin, ardeparin), fondaparinux, danaparoid
  • Direct thrombin inhibitors: L lepirudin, bivalirudin, and argatroban.
• Oral anticoagulants:
  • Coumarin derivatives: Bishydroxycoumarin, Warfarin sodium, Acenocoumarol, Ethyl biscoumacetate
  • Direct factor Xa inhibitor: Rivaroxaban
  • Oral direct thrombin inhibitor: Dabigatran etexilate

2. Used in vitro

• Heparin
• Calcium complexing agents: Sodium citrate, sodium oxalate, sodium edentate.

Question 3. Write The Basis Of Heparin Is Given Initially Before Warfarin.
Answer:

Warfarin works by being an antagonist to vitamin K. Vitamin K is the cofactor in the production of vitamin K-dependent clotting factors (factors II, VII, IX, and X).

However, the anticoagulant enzymes Protein C and S are also dependent on vitamin K and have shorter half-lives than the clotting factors II, IX, and X leading to paradoxical hypercoagulability at the initiation of therapy.

Thus, when warfarin is started first, there is a paradoxical initial prothrombotic effect. Heparin act by activating antithrombin III in plasma.

Normally antithrombin III inactivates several clotting factors, most importantly factor Xa and IIa (thrombin) but the reaction is very slow.
Heparin accelerates this inactivation process by binding to antithrombin III.

Only conformational change is required for the inactivation of factor Xa whereas the inactivation of thrombin is also dependent on the formation of scaffolding by HEPA- rin (that binds both antithrombin III and thrombin).

Heparin provides this scaffolding and thus inhibits both factors IIa and Xa. As heparin is inhibiting already activated factors, there is no time lag between the administration and action of this drug.

Therefore it can be used for the initiation of anticoagulant therapy before warfarin.