Source / episode info
- **Episode:**433
- **Title:**Divine Intervention Episode 433: Adverse Drug Reactions for The USMLE exams Part 2 (Step 1-3)
- **Published:**2022-12-31
- Source:Episode page
One-liner
This episode reviews high-yield adverse drug reactions affecting the blood components, covering megaloblastic anemia from folate/B12 deficiency; hemolytic episodes due to oxidative stress or immune complexes; and various cytopenias (agranulocytosis, thrombocytopenia) linked to specific drugs.
High-yield summary
- Megaloblastic Anemia: Caused by impaired DNA synthesis (folate or B12 deficiency). Key culprits include antifolates (Methotrexate, TMP-SMX), anti-epileptics (Phenytoin, Carbamazepine), and drugs inhibiting ribonucleotide reductase (Hydroxyurea).
- G6PD Deficiency: Leads to acute hemolytic episodes triggered by oxidative stress agents (e.g., Primaquine, Isoniazid, Dapsone, Sulfonamides). The hemolysis is non-immune mediated, resulting in a negative Coombs test.
- Autoimmune Hemolytic Anemia (AIHA): Drug-induced AIHA often involves Type II hypersensitivity reactions. Key drugs include cell wall inhibitors (Penicillins/Cephalosporins) and certain antihypertensives (Methyldopa). This type yields a positive direct Coombs test.
- Antiplatelet Agents: Drugs target different phases of primary hemostasis: Aspirin (COX inhibition -> reduced Thromboxane A2); P2Y12 inhibitors (Clopidogrel, Ticagrelor) block the ADP receptor; GPIIb/IIIa inhibitors (Abciximab) block fibrinogen binding.
- Cytopenias: Drugs can cause specific cytopenias: Agranulocytosis (e.g., Clauzapine, Dapsone); Thrombocytopenia (Heparin -> HIT).
Learning objectives
- Identify the mechanism of megaloblastic anemia associated with various drugs and deficiencies (B12/Folate).
- Differentiate between drug-induced hemolytic anemias based on their underlying pathophysiology (oxidative stress vs. immune complex formation).
- Recall specific drugs associated with severe cytopenias, such as agranulocytosis or thrombocytopenia.
- Understand the phases of primary hemostasis and how different antiplatelet agents target them.
- Recognize drug-induced hypersensitivity syndromes like DRESS syndrome and AIHA.
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