Clinical uses and adverse effects of antiarrhythmic drugs

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Clinical uses and adverse effects of antiarrhythmic drugs will be discussed here:

Clinical uses of antiarrhythmic drugs

  1. Class I drugs: Qunidine and procainamide are seldom used in arrhythmias now because of their side effects. Disopyramide is used in atrial fibrillation. Lignocaine is used intravenously to treat ventricular tachycardia and prevent ventricular fibrillation. (Preparations containing adrenaline along with lignocaine should not be used).
  2. Class II drugs: These drugs are used in patients recovering from myocardial infarction. They are also used prophylactically against recurrent tachycardia.
  3. Class III drugs: These drugs are useful in supraventricular and ventricular arrhythmias.
  4. Class IV drugs: Verapamil is used to prevent recurrence of supraventricular tachycardia, to reduce ventricular rate in patients with atrial fibrillation. These drugs are dangerous and ineffective in ventricular arrhythmias.

Adverse effects of antiarrhythmic drugs

One of the most common and serious adverse cardiac effects is proarrhythmia (arrhythmia ironically precipitated by antiarrhythmic therapy) which can occur in 5-20% of patients treated with Class I and Class III drugs.

  1. Class I drugs (Sodium-channel blockers):
    • Proarrhythmic effect
    • Dose-dependent negative inotropic effect
    • Subclass IA (especially quinidine) – Torsades de pointes (“twisting of the points”):
      • Usually occurs within the first week of therapy
      • Pre-existing prolonged QT intervals may be indicator of susceptibility
      • Potentiated by bradycardia
      • Often associated with concurrent electrolyte disturbances (hypokalemia, hypomagnesemia)
    • Subclass IC – Ventricular tachycardia
  2. Class II drugs (Beta-blockers):
    • Sinus bradycardia
    • Atrioventricular block
    • Depression of left ventricular function
  3. Class III drugs (Potassium-channel blockers):
    • Sinus bradycardia
    • Torsades de pointes
  4. Class IV drugs (Calcium-channel blockers):
    • Atrioventricular block
    • Negative inotropic action

Extra-cardiac Adverse effects

Severe extra-cardiac effects are also common with the antiarrhythmics; these tend to be drug-specific.

  1. Class I drugs
    1. Class IA drugs
      • Quinidine
        • Associated with cinchonism, a syndrome characterized by nausea, vomiting, diarrhea and a variety of CNS effects (tinnitus, headache, auditory and visual disturbances, and vertigo), Hypotension, Can cause elevated serum digoxin concentrations, hypersensitivity reactions (rashes, fever, angioneurotic edema, hepatitis) and reversible thrombocytopenia
      • Procainamide
        • Hypotension, Lupus like syndrome, gastrointestinal symptoms, Adverse CNS effects, Hypersensitivity reactions: fever, agranulocytosis (can lead to fatal infections)
    2. Class IB drugs
      • Lidocaine
        • CNS effects: CNS depression or CNS stimulation
      • Phenytoin
        • Neurological effects: drowsiness, ataxia, vertigo, nausea, nystagmus
    3. Class IC drugs
      • Encainide, flecainide
        • Neurological effects (10-15% with flecainide): Dizziness, tremor, agitation, headache, visual disurbances
        • G.I. upset
  2. Class II drugs
    • Bronchospasm, sudden withdrawal can precipitate angina, a cardiac arrhythmia, or myocardial infarction
    • Acebutolol associated with arthritis, myalgia, arthalgia, lupus-like syndrome, pulmonary complications
  3. Class III drugs
    • Amiodarone
      • Pulmonary toxicity and fibrosis, hepatic dysfunction
      • Asymptomatic corneal deposits occur in all patients
      • Many CNS symptoms
      • Hypothyroidism or hyperthyroidism
      • Cutaneous photosensitivity and blue-grey discoloration of skin
      • Peripheral neuropathy
      • Enhances the effect of warfarin and increases the serum concentrations of digoxin, quinidine, procainamide, and other drugs
    • Bretylium
      • Hypotension,Increased sensitivity to catecholamine
  4. Class IV drugs
    • Verapamil
      • Hypotension, Dizziness, headache, fatigue, Peripheral edema, G. I. effects, can increase serum concentrations of digoxin and may interact with many other drugs
    • Diltiazem
      • Hypotension, but fewer g.i. effects than verapamil
  5. Other agents
    • Digoxin
      • Many adverse side effects: Anorexia, nausea, vomiting, diarrhea, abdominal pain, headache, confusion, abnormal vision
    • Adenosine
      • hypotension, flushing, Transient dyspnea, chest discomfort (non-myocardial)  and Metallic taste.

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