Core64: Drug-induced adverse reaction: QT prolongation

🫀 High-yield / 要点：QT prolongation is a rare but potentially life-threatening proarrhythmic adverse effect because it predisposes to torsades de pointes.

Definition / 定義

• QT prolongation = prolonged ventricular repolarization.
• High-risk warning signs listed in the lecture:
  • QT prolongation > 50 ms
  • QTc > 500 ms

Why it matters / なぜ重要か

• Prolongation of repolarization predisposes to:
  • Polymorphic ventricular tachycardia
  • Torsades de pointes
• This can lead to:
  • Syncope.
  • Sudden cardiac death.

Congenital vs acquired / 先天性と後天性

• Congenital long QT syndrome:
  • Due to abnormal ion channel function.
  • Causes prolonged phase III repolarization.
  • Important cause of syncope and sudden cardiac death in children/adolescents.
  • Often triggered by physical activity or emotional stress.
• Acquired long QT:
  • Most common form in pharmacology.
  • Usually drug-induced.

Drugs causing QT prolongation / QT延長を起こす薬

Group	Examples
Antibiotics	Macrolides, quinolones, trimethoprim-sulfamethoxazole, ampicillin
Antimycotics	Fluconazole, ketoconazole
NSAID	Diclofenac
β2 agonists	Fenoterol, salbutamol, salmeterol
Antiemetics	Domperidone, ondansetron, granisetron
Antidepressants	TCAs, tetracyclic antidepressants, serotonin reuptake inhibitors
Antiepileptics	Phenytoin, felbamate
Diet / supplements	Grapefruit, flavonoids

Remember / 覚え方

• QT prolongation → torsades risk
• Macrolides, quinolones, azoles, antiemetics are classic causes
• QTc >500 ms is a major danger sign