USMLE Guide: Hematologic Medications

Introduction

This guide aims to provide an overview of hematologic medications commonly encountered in clinical practice. It covers the classification, mechanism of action, indications, and side effects of these medications. Familiarity with these medications is crucial for usmle step 1, Step 2 CK, and Step 3 exams, as well as for clinical practice.

Table of Contents

1. Anticoagulants
2. Antiplatelet Agents
3. Thrombolytics
4. Hematopoietic Growth Factors
5. Iron Preparations
6. References

Anticoagulants

Anticoagulants are medications used to prevent the formation of blood clots or to treat existing clots. They work by interfering with various steps in the coagulation cascade. The main classes of anticoagulants include:

• Heparin: Binds to antithrombin III, which inactivates thrombin and factor Xa. It is administered parenterally and has a rapid onset of action. Monitor the activated partial thromboplastin time (aPTT) during therapy.

• Low Molecular Weight Heparin (LMWH): Similar to heparin, but with more selective factor Xa inhibition. LMWH has a longer half-life, allowing for once or twice-daily dosing. Monitoring is not required.

• Warfarin: Inhibits the synthesis of vitamin K-dependent clotting factors (II, VII, IX, X) by interfering with the epoxide reductase enzyme. It has a delayed onset of action and requires monitoring of the international normalized ratio (INR).

• Direct oral anticoagulants (DOACs): Includes direct thrombin inhibitors (e.g., dabigatran) and factor Xa inhibitors (e.g., rivaroxaban, apixaban). These newer agents have a rapid onset of action, predictable pharmacokinetics, and do not require routine monitoring.

antiplatelet agents

Antiplatelet agents inhibit platelet aggregation and are used to prevent arterial thrombosis. The commonly tested medications include:

• Aspirin: Irreversibly inhibits cyclooxygenase-1 (COX-1), blocking the synthesis of thromboxane A2. It is commonly used for primary and secondary prevention of cardiovascular events.

• ADP Receptor Inhibitors: Examples include clopidogrel, prasugrel, and ticagrelor. These agents block the ADP receptor on platelets, impairing their activation and aggregation.

• Glycoprotein IIb/IIIa Inhibitors: Medications like abciximab, eptifibatide, and tirofiban block the final common pathway of platelet aggregation by inhibiting glycoprotein IIb/IIIa receptors.

Thrombolytics

Thrombolytics are used to dissolve existing blood clots, especially in cases of acute myocardial infarction and acute ischemic stroke. The commonly tested thrombolytic agent is:

• Alteplase: A recombinant tissue plasminogen activator (tPA) that converts plasminogen to plasmin, leading to fibrinolysis. Alteplase has a narrow therapeutic window and must be administered within a specific time frame.

Hematopoietic Growth Factors

Hematopoietic growth factors stimulate the production of various blood cell lines. The key medications in this category are:

• Erythropoiesis-Stimulating Agents (ESAs): Examples include epoetin alfa and darbepoetin alfa. They stimulate red blood cell production and are used in the treatment of anemia associated with chronic kidney disease, chemotherapy-induced anemia, and other conditions.

• Granulocyte-Colony Stimulating Factors (G-CSFs): Medications like filgrastim and pegfilgrastim stimulate the production and function of neutrophils. They are commonly used to reduce the risk of infection in patients undergoing chemotherapy.

Iron Preparations

Iron preparations are used in the treatment of iron-deficiency anemia. Commonly tested medications include:

• Oral Iron: Ferrous sulfate,