Oral Anticoagulants

Question 1. Write In Brief About Oral Anticoagulants.
Answer:

Oral anticoagulants are the drugs that prevent coagulation, i.e. it stops blood from clotting.
The following are the oral anticoagulants:
- Coumarin derivatives: Warfarin, Dicoumarol
- Indandione derivatives: Phenindione
- Oral direct thrombin inhibitor: Dabigatran etexilate
Oral anticoagulants are used only in vivo.
These drugs act indirectly by interfering with the synthesis of vitamin K-dependent clotting factors in the liver.
They act as a competitive antagonist of vitamin K and decrease plasma levels of active clotting factors in their dose-dependent manner.
Oral anticoagulants should not be given with barbiturates or carbamazepine or rifampicin or griseofulvin as these drugs decrease the anti-coagulant effect of oral anticoagulants.
In oral anticoagulants, coumarin derivatives are most commonly used.
Dabigatran etexilate remains a prodrug and gets converted to dabigatran. This drug leads to the reversible inhibition of thrombin. It is indicated in the prevention and treatment of venous thromboembolism.

Question 2. Describe the Mechanism Of Action And Adverse Effects Of Heparin.
Answer:

Mechanism Of Action Of Heparin

It acts indirectly by activating plasma antithrombin III and maybe other similar cofactors. The heparin antithrombin III complex then binds to clotting
factors of the intrinsic and common pathways (Xa, lla, lXa, Xla, Xlla, and Xllla) and inactivates them but not factor VIIa operative in the extrinsic pathway. At low concentrations of heparin, factor Xa-mediated conversion of prothrombin to thrombin is selectively affected. The anticoagulant action is exerted mainly by inhibition of factor Xa as well as the thrombin-mediated conversion of fibrinogen to firing.
Low concentrations of heparin prolong aPTT without significantly prolonging PT. High concentrations prolong both. Thus, low concentrations interfere selectively with the intrinsic pathway, affecting amplification and continuation of clotting, while high concentrations affect the common pathway as well.

Adverse Effects Of Heparin

Bleeding due to overdose is the most serious complication of heparin therapy. Hematuria is generally the first sign.
Thrombocytopenia is another common problem. Generally, it is mild and transient; occurs due to the aggregation of platelets.
Transient and reversible alopecia is infrequent. Serum transaminase levels may rise.
Osteoporosis may develop on long-term use of relatively high doses.
Hypersensitivity reactions are rare—urticaria, rigor, fever, and anaphylaxis. Patients with allergic diathesis are more liable.

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