Warfarin (Vitamin K Antagonists): Pharmacology

● Drugs affecting Hemostasis:
• Heparin, LMWH & Fondaparinux: https://youtu.be/TacjRFCNDeI
• Warfarin (Vitamin K Antagonists): (Current video)
• Fibrinolytics & Antifibrinolytics: https://youtu.be/IIQyw-Rkdf4
• Antiplatelet Drugs: https://youtu.be/TJp7DTMWCx0

● Hemostasis Physiology:
• Vitamin K: Biochemistry/Pharmacology: https://youtu.be/r90ptZSF6q0
• Platelet Plug Formation: https://youtu.be/zfut06No5xE
• Blood Coagulation Cascade: https://youtu.be/3LY_-c7YSjU
• Clot Retraction & Fibrinolysis: https://youtu.be/zOvq1x9rbt4
• Anticoagulant Factors: https://youtu.be/ja_XiXsYfbw

This video is on pharmacology of warfarin. Warfarin is an oral anticoagulant. Mechanism of action of warfarin is inhibition of synthesis of vitamin K dependant clotting factors. These factors are factor II, VII, IX and X. It is done by inhibiting vitamin K epoxide reductase. There is a delay of about 3-4 days in response after starting the treatment. So, during this patient is covered with heparin. In pharmacokinetics, its absorption through intestine is almost 100%. Its more than 99% protein bound. And elimination occurs mainly by CYP2C9. Its response is affected by so many factors, among factors that increase the response are vitamin K deficiency which might be due to decreased dietary intake, antibiotic use or malabsorption, displacement of warfarin from plasma protein by sulphonamide, phenytoin, valproate, probenecid etc, liver disease, third generation cephalosporines and salicylates, hyperthyroidism, enzyme inducers like cimetidine, amiodarone, disulfiram, erythromycin, metronidazole etc and defect in CYP2C9. Among factors that decreases the warfarin response are: increased vitamin K intake in diet, cholestyramine and habitual use of liquid paraffin, mutation if vitamin K epoxide reductase, pregnancy and oestrogen containing oral contraceptives, hypothyroidism, enzyme inducers like barbiturates, rifampin, griseofulvin, carbamazepine etc and finally nephrotic syndrome. Warfarin should be used cautiously in these situations. Warfarin is used in pulmonary embolism, deep vein thrombosis, post MI patients, unstable angina, atrial fibrillation, after cardiac valve replacement and cerebrovascular diseases. Monitoring of warfarin therapy is done with INR. It should be maintained from 2 to 3. Adverse events with warfarin are bleeding, skin necrosis due to transient imbalance between pro and anti-coagulant factors, purple toe syndrome and foetal warfarin syndrome. Bleeding due to warfarin or its overdose can be treated by its specific antidote, vitamin K. Response of vitamin K takes 6-24 hours to appear. Whole blood, plasma or concentrates of clotting factors show immediate response. Contraindications of warfarin are pregnancy, bleeding disorder, hypertension, subacute bacterial endocarditis, peptic ulcer, bleeding piles, tuberculosis, threatened abortion, recent eye or brain surgery or lumber puncture and hypersensitivity to warfarin.

DISCLAIMER: This video is for education purpose only. Although every effort is made to ensure accuracy of material, viewer should refer to the appropriate regulatory body/authorised websites, guidelines and other suitable sources of information as deemed relevant and applicable. In view of possibility of human error or changes in medical science, any person or organization involved in preparation of this work accepts no responsibility for any errors or omissions or results obtained from use of information in this video.

Видео Warfarin (Vitamin K Antagonists): Pharmacology канала Nonstop Neuron