Pharmacology Lecture 8: Antiarrhythmic Drugs

Course Information

• Institution: Asian Medical Institute Memorial S. Tentishev
• Department: Interprofessional Discipline
• Subject: Basic and clinical Pharmacology
• Teacher: Temirbekova Gulnura
• Lecture: No. 8
• Theme: Antiarrhythmic drugs

Arrhythmia

• Arrhythmia is a disruption of cardiac conduction, frequency, and regularity of contractions, leading to abnormal heart function and unpleasant symptoms.
• Arrhythmias are changes in heart function that disrupt proper contraction, impacting both speed and synchronicity.

Mechanism of Action of Antiarrhythmic Drugs

• Antiarrhythmic drugs aim to normalize electrolyte conductivity through myocardial ion channels.
• Cardiomyocytes have numerous ion channels along which potassium, sodium, and chlorine ions move.
• This ion movement creates action potentials in each cell, facilitating nerve impulse conduction.

Correcting Ion Movement

• To fix disturbed ion movement, antiarrhythmic drugs reduce activity and stop the impulse cycle.
• These drugs achieve this by closing damaged ion channels and minimizing negative impacts on the heart and sympathetic receptors.

Class I Antiarrhythmic Drugs

• Class IA: Quinidine

  • Mechanism: Blocks open sodium channels, preventing sodium influx.
  • Therapeutic use: Treats various arrhythmias, including atrial fibrillation.
  • Pharmacokinetics: Rapid and complete oral absorption with extensive liver metabolism.
  • Side effects: High doses can lead to blurred vision, tinnitus, headaches, disorientation, and psychosis.

• Class IB: Lidocaine and Mexiletine

  • Mechanism: Quick binding and dissociation with sodium channels.
  • Pharmacokinetics: Lidocaine is given intravenously due to liver metabolism preventing oral administration.
    • Drugs inhibiting liver function (e.g., beta-blockers) may require lidocaine dose adjustment. Mexiletine is easily absorbed orally.
  • Side effects: Nausea, vomiting, and dyspepsia are typical side effects.

• Class IC: Flecainide and propafenone

  • Mechanism: Blocks potassium channels, increasing action potential duration.
  • Effects: Active even at normal heart rate.
  • Therapeutic use: For maintaining sinus rhythm and in specific types of arrhythmias.
  • Pharmacokinetics: Oral absorption, with potential dosage adjustments in renal failure.
  • Side effects: Often well-tolerated; dizziness and nausea are common.

Class II Antiarrhythmic Drugs

• β-blockers: Prevent life-threatening ventricular arrhythmias (e.g., after myocardial infarction).
• Metoprolol: Commonly used to treat cardiac arrhythmias, extensively metabolized by the liver.
• Esmolol: Very short-acting β-blocker, ideal for managing emergency arrhythmias, administered intravenously.

Class III Antiarrhythmic Drugs

• Potassium channel blockers (e.g., Amiodarone): Effective against refractory supraventricular and ventricular tachyarrhythmias.
• Amiodarone: Used to manage fibrillation or atrial flutter.
• Pharmacokinetics: Long duration of action, distributed in adipose tissue, and requires several months to achieve full effect.
• Side effects: Potential for various toxic effects, including pulmonary fibrosis, neuropathy, and hepatotoxicity; careful monitoring and controlled dosage are crucial.
• Sotalol: Acts as both a class III agent and a non-selective beta-blocker. Used for maintaining a normal sinus rhythm in atrial fibrillation, typically in those needing preventative treatment in cases of left ventricular hypertrophy or atherosclerotic heart disease.

Class IV Antiarrhythmic Drugs

• Calcium channel blockers (e.g., Verapamil): Primarily affect smooth muscle of blood vessels and the heart.
• Verapamil: Has greater impact on the heart and is more effective for atrial than ventricular arrhythmias.

Other Antiarrhythmic Drugs

• Magnesium sulfate: Used intravenously to manage arrhythmias because oral magnesium is ineffective for arrhythmia treatment. Necessary for sodium, calcium, and potassium transport through cell membranes.

This quiz covers Lecture No. 8 on Antiarrhythmic drugs from the Basic and Clinical Pharmacology course. You will explore the mechanisms of action for these drugs and their impact on cardiac conduction and rhythm. Prepare to test your understanding of how these medications restore normal heart function.