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Toxicology – Cardiotoxic Drugs
Sodium Channel Blockers (Widened QRS)
Several drugs impair cardiac conduction by blocking sodium channels, leading to QRS widening on ECG. These include antihistamines, antimalarials, tricyclic antidepressants, cocaine, and local anesthetics.
QT Prolonging Agents
Certain medications delay cardiac repolarization, resulting in QT interval prolongation and risk of torsades de pointes. Common examples include antipsychotics, macrolide antibiotics, and methadone.
Beta-Blockers
These agents reduce heart rate and conduction through β-adrenergic blockade, potentially causing bradycardia and varying degrees of heart block in overdose.
Calcium Channel Blockers
By inhibiting calcium influx into cardiac cells, these drugs decrease contractility and conduction, leading to bradycardia and heart block.
Digoxin
Digoxin inhibits the Na⁺/K⁺-ATPase pump, increasing intracellular calcium. Toxicity can result in bradycardia, heart block, and potentially life-threatening ventricular arrhythmias.
Antiarrhythmic Drugs
Antiarrhythmics are categorized based on their electrophysiologic effects:
Chemotherapeutic Agents
Certain cancer treatments are associated with cardiotoxicity:
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Sodium Channel Blockers (Widened QRS)
Several drugs impair cardiac conduction by blocking sodium channels, leading to QRS widening on ECG. These include antihistamines, antimalarials, tricyclic antidepressants, cocaine, and local anesthetics.
QT Prolonging Agents
Certain medications delay cardiac repolarization, resulting in QT interval prolongation and risk of torsades de pointes. Common examples include antipsychotics, macrolide antibiotics, and methadone.
Beta-Blockers
These agents reduce heart rate and conduction through β-adrenergic blockade, potentially causing bradycardia and varying degrees of heart block in overdose.
Calcium Channel Blockers
By inhibiting calcium influx into cardiac cells, these drugs decrease contractility and conduction, leading to bradycardia and heart block.
Digoxin
Digoxin inhibits the Na⁺/K⁺-ATPase pump, increasing intracellular calcium. Toxicity can result in bradycardia, heart block, and potentially life-threatening ventricular arrhythmias.
Antiarrhythmic Drugs
Antiarrhythmics are categorized based on their electrophysiologic effects:
- Class I: Sodium channel blockers (Ia prolong action potential, Ib shorten it, Ic have minimal effect)
- Class II: Beta-blockers
- Class III: Potassium channel blockers (prolong repolarization)
- Class IV: Calcium channel blockers
Chemotherapeutic Agents
Certain cancer treatments are associated with cardiotoxicity:
- 5-Fluorouracil (5-FU): Can cause arrhythmias and congestive heart failure
- Anthracyclines (e.g., doxorubicin, epirubicin): Associated with cardiomyopathy and heart failure
- Cisplatin: May lead to acute myocardial infarction
- Cyclophosphamide: Can cause acute cardiac failure and heart failure
- Taxanes (e.g., paclitaxel, docetaxel): Linked to arrhythmias and heart failure
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