Getting to know Antiarrhythmic Medication Group III


Medications that prevent or treat cardiac arrhythmias are called antiarrhythmics. Antiarrhythmic drugs are classified according to their use in 5 groups.

Group III includes potassium channel blockers with effects that extend potential action. This causes an extension of the QT interval, which increases the risk of Torsades de Pointes (TDP), which can cause lethal ventricular arrhythmias. Class III agents commonly used for the maintenance of normal sinus rhythms include:


  • Amiodarone
  • Dronedarone
  • Sotalol
  • Dofetilide

How do group III antiarrhythmics work?

Potassium channel blockers work by inhibiting the K + channel which increases the refractory period. This increases the duration without affecting phase 0 and resting the membrane potential. Potassium channel blockers include class III antiarrhythmic compounds that bind and block potassium channels responsible for phase 3 repolarization. Inhibiting the channel slows repolarization and results in an increased duration of potential action and effective refractory periods.

What are the side effects of group III antiarrhythmics?

All of these compounds, such as group III compounds, prioritize proarrhythmic and antiarrhythmic. For example, an increase in the duration of potential action can produce Torsades de Pointes (a type of ventricular tachycardia) especially in patients with the long-QT syndrome. Amiodarone, due to its class IV effects, can cause bradycardia and atrioventricular barriers and has contraindications in patients with cardiac arrest or sinoatrial node dysfunction. Side effects that you can experience include:


  • Extension of the QT interval
  • Because it is similar to thyroxine, drugs can interfere with thyroid function, causing hypo or hyperthyroidism
  • As a result of a larger VD, bound, and deposited on the cornea, it causes vision problems and photophobia
  • Having a tendency to deposit on the skin, can make it sensitive to sunlight. Discoloration occurs in areas exposed to prolonged administration (due to iodine content)
  • In prolonged administration, lung fibrosis can occur
  • Liver damage can occur due to metabolism in the liver

Things to note


Always consult with a doctor before using group III antiarrhythmics. Inform your doctor if you are or are planning to become pregnant or are breastfeeding. Also tell the doctor what treatment you are using, including natural and herbal supplements. Tell your doctor if you have allergies to group III antiarrhythmic treatment.

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