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Farmacología de hemostasia y coagulación
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Farmacología de hemostasia y coagulación

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This section introduces the topic of the coagulation system and its pharmacological aspects, emphasizing the importance of understanding medications used to manage thrombotic or hemorrhagic conditions.

The Coagulation System and Hemostasis

  • The coagulation system is essential for hemostasis, preventing blood loss from damaged blood vessels within the cardiovascular system.
  • The hemostatic process involves four phases: vascular constriction, platelet activation and aggregation, fibrin network formation, and fibrinolysis for clot dissolution.
  • Platelets play a crucial role in hemostasis by adhering to endothelial cells and forming a platelet plug to stop bleeding.

Understanding Coagulation Pathways

This section delves into the intrinsic and extrinsic pathways of coagulation, highlighting the activation of various factors leading to clot formation.

Intrinsic and Extrinsic Pathways

  • Coagulation involves intrinsic (factor 12-initiated) and extrinsic (tissue factor-initiated) pathways that converge at factor 10 activation for clot formation.
  • Evaluation of these pathways is done through partial thromboplastin time (PTT) for intrinsic pathway assessment and prothrombin time (PT) for extrinsic pathway evaluation using INR as a critical parameter.

Vitamin K Dependent Factors in Coagulation

Discusses vitamin K-dependent factors crucial in coagulation regulation, emphasizing their synthesis in the liver and their roles in both pro-coagulant and anti-coagulant processes.

Vitamin K Dependence

  • Factors like 7, 9, 10, and 2 are dependent on vitamin K for activation within the liver.

Understanding Coagulation Disorders

In this section, the speaker discusses coagulation disorders, focusing on thrombosis and the formation of blood clots within blood vessels.

Thrombosis and Blood Clot Formation

  • The absence of anticoagulants can lead to the formation of a large clot that completely blocks a blood vessel, causing thrombosis. Thrombosis is the pathological formation of a hemostatic plug within a blood vessel in the absence of bleeding.
  • Patients with coagulation imbalance may experience spontaneous activation of the coagulation system due to deficiencies in proteins like protein C, protein S, or antithrombin 3. This imbalance can result in vascular occlusion by venous clots.
  • Blood clots can develop into emboli that may lodge in various locations such as the lungs (pulmonary embolism), lower limbs, or brain. These clots can be arterial or venous and exhibit distinct morphological characteristics.

Characteristics of Arterial and Venous Clots

  • Arterial clots are typically white with platelets and leukocytes, associated with atherosclerosis, leading to ischemia due to their presence in arteries responsible for tissue perfusion. On the other hand, venous clots have a dark red color and consist of three parts: head, body, and tail.

Medications for Coagulation Regulation

  • Coagulation disorders primarily manifest as hemorrhagic or thrombotic diseases. Medications used for thrombotic conditions aim to prevent coagulation system activation or dissolve formed clots through anticoagulants and thrombolytics.
  • In cases like hemophilia where there is a deficiency in clotting factors like factor VIII or von Willebrand factor, medications are employed to prevent bleeding episodes by replacing deficient factors synthetically.

Understanding the Mechanism of Heparin

In this section, the mechanism of action of heparin is discussed, focusing on its interaction with antithrombin 3 and thrombin.

Mechanism of Action

  • Heparin blocks the action of antithrombin 3 by inhibiting thrombin activity.
  • Heparin binds to antithrombin 3, facilitating its action against thrombin and preventing their complete assembly.
  • Heparin disrupts the assembly between antithrombin 3 and thrombin, inhibiting thrombin activation.

Administration and Elimination of Heparin

This part delves into the administration, elimination, and characteristics of heparin.

Administration and Elimination

  • Heparin is administered subcutaneously or intravenously; it binds to plasma proteins, endothelial cells, and macrophages.
  • Elimination occurs through despolimerization in endothelial cells and reticuloendothelial system; renal excretion is slow.

Monitoring Anticoagulant Effects of Heparin

The monitoring process for assessing the anticoagulant effects of heparin is explained.

Monitoring Process

  • Anticoagulant response is monitored using activated partial thromboplastin time (aPTT).
  • Dosing adjustments are made to achieve a 1.5 to 2.5 times increase in baseline aPTT levels for effective anticoagulation.

Clinical Applications and Adverse Effects

This segment covers the clinical uses and potential adverse effects associated with heparin therapy.

Clinical Applications and Adverse Effects

  • Heparin is used for venous thrombosis, pulmonary embolism, acute coronary syndromes, arterial thrombosis, hemodialysis procedures.

Understanding Heparin and its Mechanism of Action

In this section, the discussion revolves around the mechanism of action of heparin, particularly focusing on how different sizes of heparin molecules affect their ability to inhibit thrombin.

Heparin Size and Mechanism

  • Large heparin molecules are required to inactivate thrombin effectively by binding to antithrombin.
  • Small heparin molecules lack the capacity to completely envelop thrombin, affecting their inhibitory action.

Advantages of Low Molecular Weight Heparin

This part highlights the advantages of low molecular weight heparin over unfractionated heparin, emphasizing factors like monitoring requirements and pharmacological properties.

Advantages of Low Molecular Weight Heparin

  • Does not necessitate continuous laboratory monitoring due to its stable pharmacological action.
  • Exhibits high bioavailability and a longer half-life (12 hours), allowing for less frequent dosing compared to unfractionated heparin.
  • Shows reduced platelet function inhibition and lower incidences of thrombocytopenia and thrombosis.

Types and Administration of Low Molecular Weight Heparins

This segment delves into specific types of low molecular weight heparins, their administration methods, pharmacokinetics, and cost considerations.

Low Molecular Weight Heparins

  • Delta parina, enoxaparin, and tinzaparin are common variants; enoxaparin is widely used in various subcutaneous doses for ease of administration.
  • These synthetic analogues have high bioavailability (80-90%), renal elimination, shorter half-lives (4 hours), and require administration every 12 hours.

Direct Thrombin Inhibitors: Types and Considerations

The focus shifts towards direct thrombin inhibitors like bivalirudin ximelagatran melagatran davatran, discussing their availability in the market along with associated costs.

Direct Thrombin Inhibitors

  • Davatran is commonly used due to its oral administration route but faces limitations due to cost implications.
  • Recombinant hirudins are rarely utilized globally due to limited availability; ximelagatran was previously used but is now obsolete.

Comparative Analysis: Warfarin vs. Dabigatran

A comparison between warfarin and dabigatran is presented regarding dosing requirements, monitoring needs, efficacy in conditions like atrial fibrillation, and current usage trends.

Warfarin vs. Dabigatran

  • Dabigatran offers advantages over warfarin with no need for monitoring or dosage adjustments in certain conditions like atrial fibrillation.

Anticoagulants Overview

In this section, the speaker discusses various types of anticoagulants and their mechanisms of action, focusing on drugs like apixaban, rivaroxaban, warfarin, and acenocoumarol.

Anticoagulant Classification

  • Atrial fibrillation is not a substrate for protein P in the kidney or gastrointestinal tract.
  • Apixaban belongs to the group of direct factor Xa inhibitors with oral administration and hepatic elimination.
  • Rivaroxaban, another factor Xa inhibitor, has a shorter half-life than apixaban and is administered once daily.
  • Rivaroxaban is widely used due to its convenience with a 24-hour dosing regimen.
  • Warfarin and acenocoumarol are cost-effective vitamin K antagonists commonly used in different regions.

Mechanism of Action

  • Warfarin inhibits post-translational carboxylation of liver-synthesized clotting factors by opposing vitamin K action.
  • Vitamin K acts as a cofactor for epoxide reductase in activating clotting factors; warfarin disrupts this process.
  • Factors affected by vitamin K antagonists include factors 2, 7, 9, and 10 involved in coagulation cascade regulation.

Warfarin Administration and Monitoring

This part delves into the administration protocols for warfarin therapy including dosage adjustment based on INR monitoring.

Warfarin Therapy Management

  • Warfarin's low cost makes it popular despite individualized dosing requirements for each patient.
  • Initial warfarin treatment effects appear after several days necessitating concurrent enoxaparin use initially.
  • INR monitoring guides dosing adjustments aiming for values between 2 to 3.5 depending on the condition.
  • Patients receive personalized treatment cards outlining dosing schedules during initial dose determination phase.

Pharmacokinetics and Drug Interactions

  • Warfarin undergoes slow metabolism via cytochrome P450 with onset around 36 hours post-administration.

Detailed Discussion on Anticoagulants and Their Effects

In this section, the speaker discusses the impact of various medications on anticoagulants like warfarin, focusing on factors such as vitamin K synthesis, drug interactions, and adverse effects.

Impact of Medications on Anticoagulants

  • Certain oral antifungals and antibiotics can affect the availability of vitamin K due to alterations in intestinal flora, potentially increasing bleeding risk when taking warfarin.
  • Drugs that induce metabolic enzymes like cytochrome P450 can interfere with warfarin's effectiveness. Examples include barbiturates and griseofulvin.
  • The primary adverse effect of warfarin is bleeding, especially in patients with uncontrolled INR levels. Other side effects include skin rashes and potential teratogenic effects during pregnancy.

Monitoring Warfarin Action and Reversal

  • Monitoring warfarin's action involves assessing the INR levels, aiming for a range between 2 to 3 to balance thrombosis and bleeding risks.
  • Warfarin has a long half-life; if urgent surgery is needed while on warfarin, plasma transfusions or vitamin K administration may be necessary to reverse its effects.

Alternative Anticoagulant: Acenocoumarol

  • Acenocoumarol is an alternative anticoagulant similar to warfarin but with a shorter half-life. It requires individual dosing adjustments like warfarin.

Reversing Anticoagulation Effects

This section delves into methods for reversing the effects of anticoagulants like warfarin using treatments such as complex prothrombin concentrates and vitamin K administration.

Reversal Strategies for Anticoagulants

  • Complex prothrombin concentrate can help reverse anticoagulant effects by providing essential clotting factors not synthesized due to medication interference.
  • Adjusting anticoagulant doses based on INR levels can aid in restoring normal coagulation function. Vitamin K administration may be necessary in cases of bleeding episodes.

Managing High INR Levels

  • High INR levels require dose adjustments or additional vitamin K doses. Close monitoring post-administration is crucial to ensure proper coagulation balance.

Pharmacology Overview

In this section, the speaker discusses the administration of various medications related to coagulation and platelet function.

Administering Coagulation Medications

  • Administration of a vial of prothrombin complex reverses the effect.
  • Vitamin K vial should be administered. Medications often come with scored lines for flexible dosing.

Anticoagulants vs. Antiplatelet Agents

  • Anticoagulants are used for venous thrombosis, while antiplatelets are for arterial thrombosis.
  • Platelets activate upon injury, releasing proteins like 2b3a and 1b9 for adhesion and aggregation.

Mechanism of Antiplatelet Drugs

  • Internal platelet granules release proteins crucial for platelet function.
  • Antiplatelet drugs prevent receptor release, inhibiting platelet adhesion and aggregation.

Antiplatelet Medications

This part delves into specific classes of antiplatelet medications and their mechanisms of action.

Types of Antiplatelet Drugs

  • Inhibitors of cyclooxygenase like Aspirin are commonly used.
  • Various drug classes include ADP receptor antagonists, thienopyridines, phosphodiesterase inhibitors, and GP2b3a receptor antagonists.

Aspirin as an Antiplatelet Agent

  • Aspirin's irreversible acetylation of cyclooxygenase blocks platelet activation cascade.
  • Aspirin prevents platelet activation by inhibiting second messenger release.

Clinical Use and Dosage

  • Aspirin is vital in preventing arterial thrombosis in conditions like myocardial infarction.

Prostaglandin and Platelet Aggregation Inhibitors

The discussion covers the role of prostaglandins, aspirin, and phosphodiesterase inhibitors in platelet aggregation inhibition.

Prostaglandin and Aspirin Interaction

  • Prostaglandins act on the upper part while Aspirin acts on the top.
  • Phosphodiesterase inhibitors work at the lower part of the cascade by directly blocking phosphodiesterase, preventing platelet adhesion and aggregation.

Antiplatelet Agents for Myocardial Infarction

This segment focuses on antiplatelet agents used in myocardial infarction treatment.

Antiplatelet Agents Usage

  • Anti-ischemic cerebrovascular accidents commonly use dipiridamol.
  • Dipiridamol's common adverse effect is headaches.

Antagonists of Glycoprotein 2B3 Receptors

Discusses antagonists targeting glycoprotein 2B3 receptors to prevent platelet aggregation.

Antagonists Functionality

  • Eptifibatide and Elim are drugs that inhibit glycoprotein 2B3 to prevent platelet aggregation.
  • These drugs bind to the receptor, preventing fibrinogen binding, thus inhibiting platelet aggregation but increasing bleeding risk.

Coagulation Factors Deficiency Treatment

Explores pharmacological preparations for coagulation factor deficiencies.

Coagulation Factor Treatments

  • Vitamin K tablets (5 mg) counteract vitamin K-blocking drugs like warfarin.
  • Plasma fractions like cryoprecipitate with high coagulation factor content treat hemophilia.

Hemostatic Agents for Bleeding Risk

Details hemostatic agents used to manage bleeding risks effectively.

Hemostatic Agent Functionality

  • Tranexamic acid stabilizes blood vessel elasticity, commonly used in von Willebrand disease.