Anticoagulants MCQs

Explanation: Urokinase is an enzyme that promotes the breakdown of blood clots by converting plasminogen into plasmin, which then degrades fibrin, the main component of clots. This fibrinolytic action helps dissolve clots in blood vessels. It is used in Pulmonary embolism, Deep vein thrombosis (DVT) etc to dissolve clots.

Explanation: Methotrexate is a structural analogue of folic acid and acts as a competitive inhibitor of dihydrofolate reductase, preventing the conversion of dihydrofolate to tetrahydrofolate, which is essential for DNA synthesis and cell division. This particularly affects rapidly dividing cells, making it useful in cancer and autoimmune diseases.

Option A: Antagonists of vitamin K are used to reduce blood coagulation in patients at risk of thromboembolism; the most widely used is warfarin. Option B: Menadione and menadiol diacetate, synthetic compounds that can be metabolized to phylloquinone. It has vitamin K activity. Option C: Menaquinones, synthesized by intestinal bacteria, with differing lengths of side chain. It has also vitamin K like activity. Option D: Tocopherol have vitamin E activity. Reference: Harper's illustrated biochemistry 32 nd edition, CH 44 PN 532

Amiodarone is an important anti-arrhythmic drug and has a well-documented ability to inhibit the hepatic metabolism of many drugs. Reference: Basic & Clinical Pharmacology by Bertram G. Katzung Fourteenth Edition Pg no.60

Rifampin strongly induces most cytochrome P450 isoforms (CYP1A2, 2C9, 2C19, 2D6, and 3A4), which increases the elimination of numerous other drugs including methadone, anticoagulants, cyclosporine, some anticonvulsants, protease inhibitors, some nonnucleoside reverse transcriptase inhibitors or integrase strand transfer inhibitors, contraceptives, and a host of others. Coadministration of rifampin results in significantly lower serum levels of these drugs. Reference: Basic & Clinical Pharmacology, 14th Edition By Bertram G. Katzung Page no. 845-846

Anticoagulants are of little value in thrombotic stroke. Neurological sequelae are similar whether they are given or not. Moreover, in the initial stages it is difficult to rule out haemorrhagic stroke. However, they may be given in cerebral embolism because showers of emboli are often recurrent in case of mitral stenosis/atrial fibrillation, and can be prevented by anticoagulants. Antiplatelet drugs are superior to anticoagulants in transient ischaemic attacks (TIAs).

Due to the shorter half-life of the oral factor X and thrombin inhibitors, the anticoagulant status of the patient changes rapidly. Sudden cessation of short-acting oral anticoagulants can lead to stroke . Excess bleeding is associated with taking any of the anticoagulants not with stopping them. An increase in INR reflects increased anticoagulation by warfarin. Thrombo- cytopenia is a risk associated with heparin. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 834-33

Chemical antagonist. A chemical antagonist prevents the actions of an agonist by modifying or sequestering the agonist so that it is incapable of binding to and activating its receptor. Protamine sulfate is a chemical antagonist for heparin. Reference: Basic & Clinical Pharmacology by Bertram G. Katzung Fourteenth Edition Pg no. 22