Question

Rosalie is now 20-years old and has been compliant with her treatment regimens. She approaches her doctor because of a swollen and painful leg, and the doctor fears that a venous thrombosis has formed due to her oral contraceptive. After confirmation thereof, he prescribes warfarin as treatment and ensures the dose is tapered correctly. Three weeks after starting her warfarin treatment, she decides to also start using a new multivitamin containing vitamin B12, vitamin C and vitamin K, something her doctor told her not to do. Two weeks after starting her multivitamin her swelling and pain returns. Explain i) how warfarin will treat her venous thrombosis, ii) what type of drug antagonism is occurring, and iii) how the antagonism is taking place.

Answer 1

i) Warfarin in venous thrombosis

​​​​​​warfarin acts as anticoagulant only in vivo, not in vitro.This is so because they act indirectly by interfering with the synthesis of vit K depending clotting factors in Liver.They apparently behave as competitive antagonists of vit K and lower the plasma levels of functional clotting factors in a dose-dependent manner.

In fact, they inhibit the enzyme vit K epoxide reductase (VKOR) and interfere with regeneration of the active hydroquinone form of vit K which act as a cofactor for the enzyme glutamyl carboxylase that carries out the final step of carboxylating glutamate residues of prothrombin and factors VII, IX and X. This carboxylation is essential for the ability of the clotting factor to bind Ca⁺ and to get bound to phospholipid surfaces, necessary for coagulation sequence to proceed.

By this mechanism warferin prevent venous thrombosis.

ii) Type of drug antagonism:

This is competitive drug antagonism.

Competitive mean it compete with its agonist to bind with the same binding site.

iii) How competitive inhibition occur:

I explained it in the second para of first question's answer.I gave a pic add with this for better answer.