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Pharmacology Cardiovascular Pharmacology Intermediate
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Drugs Causing QT Prolongation

A
B
C
D
E
F
G
High-yield medication classes that block hERG potassium channels (IKr), prolonging ventricular repolarization and risking Torsades de Pointes.

Drug-induced QT prolongation results predominantly from inhibition of the rapid delayed rectifier potassium current (IKr). Excessive prolongation (QTc > 500 ms) markedly increases risk of degeneration into fatal Torsades de Pointes (TdP).

Systematic Breakdown

A

Antiarrhythmics (Class IA & III)

Class IA (Quinidine, Procainamide, Disopyramide) and Class III (Amiodarone, Sotalol, Ibutilide, Dofetilide).

B

antiBiotics (Macrolides & Fluoroquinolones)

Azithromycin, Clarithromycin, Erythromycin, and Ciprofloxacin, Levofloxacin, Moxifloxacin.

C

anti-C (Citalopram & Chloroquine)

Citalopram/Escitalopram (dose-dependent QT prolongation) and Chloroquine/Hydroxychloroquine.

D

antiDepressants (Tricyclics - TCAs)

Amitriptyline, Nortriptyline, Imipramine block both sodium channels and cardiac potassium currents.

E

antiEmetics (5-HT3 Antagonists)

Ondansetron, Granisetron, Metoclopramide (especially with rapid IV bolus).

F

antiFungals (Azoles)

Fluconazole, Ketoconazole, Voriconazole (block hERG and inhibit CYP3A4 metabolism of other QT drugs).

G

anti-psychotics (Haloperidol & Ziprasidone)

Typical and atypical neuroleptics (Haloperidol, Chlorpromazine, Ziprasidone, Quetiapine).

High-Yield Clinical Pearls & Exam Tips
  • Risk factors for Torsades de Pointes: Hypokalemia, Hypomagnesemia, Hypocalcemia, Female sex, Bradycardia, and baseline QTc > 500 ms.
  • Acute management of Torsades de Pointes: IV Magnesium Sulfate (even if serum magnesium level is normal), followed by overdrive pacing if refractory.
Related Pharmaceuticals
Amiodarone Azithromycin Citalopram Ondansetron Haloperidol Magnesium Sulfate
Related Clinical Conditions
Long QT Syndrome Torsades de Pointes Ventricular Fibrillation
Authoritative Sources: First Aid USMLE Step 1 · CredibleMeds QT Drug Database · Goodman & Gilman's The Pharmacological Basis of Therapeutics

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