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Clinical pharmacy 2024/2025 Level 3 Pharm D Pharmacology 1 (PO 502)

2- Class II - Beta-blockers blockers

➢ Diminish phase 4 depolarization, thus depress automaticity

➢ Prolong AV conduction
➢ Decrease heart rate and contractility.

 Class II agents are useful in treating tachy-arrhythmias caused by increased

sympathetic activity.

 They are also used for atrial flutter and fibrillation.

 Metoprolol is the β-blocker most widely used in the treatment of cardiac arrhythmias.

3- Class III - Potassium-channel blockers

Therapeutic ➢ Amiodarone is effective in the treatment of severe supraventricular,

uses ventricular tachyarrhythmias and atrial fibrillation or flutter.

➢ Diminish the outward potassium current during repolarization of
cardiac cells.

MOA ➢ Prolong the duration of the action potential without altering phase
0 of Depolarization or the resting membrane potential.
➢ Prolong the effective refractory period.

➢ Neuropathy, hepatotoxicity, corneal deposits and hypo- or
hyperthyroidism.
Adverse ➢ Respiratory: irreversible pulmonary damage, including interstitial

effects pneumonitis
➢ Respiratory muscle impairment (due to amiodarone deposits into

lungs).
➢ Bretylium (+ adrenergic neuron blocker)
➢ Amiodarone (+ Class I, III and IV)
.
Examples
➢ Sotalol (+ β-adrenergic blocker)
.
➢ Dofetilide (pure potassium channel blocker)

- All class III drugs have the potential to induce arrhythmias.

Note:

 Amiodarone contains iodine and is related structurally to thyroxine and has complex
effects, showing class I, II, III, and IV actions.

 Dronedarone is a structurally modified version of amiodarone (lack of iodine), the
antiarrhythmic drug that has shown the greatest efficacy at maintaining sinus rhythm in

patients with paroxysmal atrial fibrillation.

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