JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D III Year PHARMACOLOGY - II Previous Question Paper (December - 2022 - R08)

Anticoagulants are classified into the following categories:

1. In vivo anticoagulants: Heparin and its derivatives (Low Molecular Weight Heparins like Enoxaparin).
2. Oral anticoagulants (Vitamin K antagonists): Coumarin derivatives (Warfarin, Acenocoumarol) and Indanedione derivatives (Phenindione).
3. Direct Oral Anticoagulants (DOACs): Direct thrombin inhibitors (Dabigatran) and Factor Xa inhibitors (Rivaroxaban, Apixaban).

Pharmacology of Heparin:

Heparin is a parenteral anticoagulant that acts by binding to antithrombin III, inducing a conformational change that accelerates the inactivation of thrombin (Factor IIa) and Factor Xa. It is administered intravenously or subcutaneously and is monitored via the Activated Partial Thromboplastin Time (aPTT). The primary adverse effect is bleeding, which can be reversed using Protamine sulfate. Heparin-induced thrombocytopenia (HIT) is a serious immune-mediated complication.

Pharmacology of Warfarin:

Warfarin is an oral anticoagulant that acts as a Vitamin K antagonist. It inhibits the enzyme Vitamin K epoxide reductase (VKORC1), preventing the recycling of Vitamin K. This leads to the production of biologically inactive clotting factors II, VII, IX, and X, and proteins C and S. Its onset of action is delayed (48-72 hours) as it only affects the synthesis of new factors. It is monitored using the International Normalized Ratio (INR). Warfarin is contraindicated in pregnancy due to teratogenicity and is reversed by Vitamin K (phytomenadione) or fresh frozen plasma in cases of severe hemorrhage.

Immunosuppressants are a class of drugs that inhibit or reduce the strength of the body's immune system. They are primarily used to prevent organ transplant rejection, treat autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus, and manage severe allergic conditions by suppressing the proliferation and activity of T-lymphocytes and other immune cells.

Calcineurin inhibitors, including Cyclosporine and Tacrolimus, are potent immunosuppressants that act by blocking the intracellular signaling pathway required for T-cell activation.

Mechanism of Action:

1. Upon antigen stimulation, intracellular calcium levels rise, activating the phosphatase enzyme calcineurin.
2. Calcineurin dephosphorylates the transcription factor NFAT (Nuclear Factor of Activated T-cells), allowing it to translocate into the nucleus.
3. In the nucleus, NFAT promotes the transcription of genes for cytokines, most notably Interleukin-2 (IL-2), which is essential for T-cell proliferation.
4. Cyclosporine binds to the intracellular protein cyclophilin, while Tacrolimus binds to FK-binding protein (FKBP-12).
5. These drug-protein complexes bind to and inhibit calcineurin, thereby preventing NFAT dephosphorylation and subsequent IL-2 production.

Pharmacokinetics: Both drugs have variable oral absorption and undergo extensive metabolism via the CYP3A4 enzyme system in the liver and gut wall. They are primarily excreted in the bile.

Clinical Uses: They are the cornerstones of immunosuppressive therapy for kidney, liver, and heart transplants, and are used in refractory autoimmune disorders.

Adverse Effects: The most significant dose-limiting toxicity is nephrotoxicity, caused by afferent arteriolar vasoconstriction. Other common side effects include hypertension, neurotoxicity (tremors, headache), hyperglycemia, and an increased risk of opportunistic infections and secondary malignancies.