Amiodarone

Amiodarone: Uses, Dosage and Side Effects

Overview

Potassium-channel blocker, an antiarrhythmic drug with secondary class 2 (beta-blocker), class 4 (calcium-channel blocker), and potent class 1 (sodium-channel blocker) activities.

How Amiodarone Works?

• Prolongs action potential duration and therefore effective refractory period in all cardiac
  tissues, including bypass tracts (class 3 action).
• Inhibits sodium channels (class 1 action).
• Blocks alpha- and beta-adrenergic receptors (class 2 action).
• Slows the sinus rate.
• Prolongs sinus node recovery time.
• Inhibits AV nodal conduction.

Uses of Amiodarone

• Treatment of ventricular arrhythmias and supraventricular arrhythmias in dogs.
• May be useful in ventricular pre-excitation syndromes because it can prolong AV nodal and bypass tract effective refractory periods.
• Used successfully for rate control or conversion to sinus rhythm in some dogs with atrial fibrillation and as an adjunct to electrical cardioversion.

Dose of Amiodarone in Dogs and Cats

Dogs:

Oral: 10–15 mg/kg p.o. q12h for 7 days, then 5–7.5 mg/kg p.o. q12h for 14 days; thereafter, 5–7.5 mg/kg p.o. q24h (loading dose leading to steady state doses). Serum amiodarone levels should be assessed at 3 weeks after starting therapy.
Intravenous: Doses of 0.03–0.05 mg/kg/min have been administered as a continuous rate infusion for cardioversion of atrial fibrillation and sustained supraventricular tachycardia non-responsive to other antiarrhythmics.

Cats: no available information

Side Effects of Amiodarone in Dogs and Cats

• Bradycardia, AV block and prolongation of the QT interval.
• It is a negative inotrope and can cause hypotension.
• Systemic side effects described in dogs include anorexia, GI disturbances, hepatotoxicity, keratopathy and positive Coombs’ test.
• Adverse effects associated with i.v. administration include pain at injection site, hypotension, hypersalivation and hypersensitivity reactions, which may be a reaction to the carrier solvent. Should i.v. preparations be considered, prior treatment with
  dexamethasone should be considered to reduce risk of anaphylactic reactions.

Contraindications of Amiodarone in Dogs and Cats

Avoid in dogs with:

• Sinus bradycardia
• AV block
• Thyroid dysfunction
• hypersensitive to it or iodine

Some Notes:

• Amiodarone is generally used when other commonly used drugs are ineffective because of its potential toxicity
• It is recommended to avoid or administer Amiodarone carefully with these drugs due to the occurrence of interactions between each other:
  • Increase serum levels and/or pharmacological effects of these drugs( Beta-blockers, Calcium-Channel Blockers, Ciclosporin, Digoxin, Lidocaine, Methotrexate and Theophylline).
  • Cimetidine may increase serum levels of amiodarone.
  • Opioids (fentanyl, morphine): may cause hypotension, bradycardia
  • General Anesthetics (Isoflurane, Propofol): increases possibility of occurrence of hypotension or arrhythmias
  • Antiarrhythmics (disopyramide, procainamide, quinidine, sotalol), Azole antifungals, Cisapride, Antibiotics (moxifloxacin,azithromycin, erythromycin): Cause more cardiac arrhythmias if given together.