Amiodarone: Dosage, Uses, and Side Effects

Amiodarone for Dogs, Cats, and Horses: Dosage, Uses, and Side Effects Guide

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

• Dogs:
  • Treatment of ventricular arrhythmias and supraventricular arrhythmias.
  • Effective in ventricular pre-excitation syndromes by prolonging AV nodal and bypass tract refractory periods.
  • Used for rate control or conversion to sinus rhythm in dogs with atrial fibrillation, as an adjunct to electrical cardioversion.
  • Combined with itraconazole for Trypanosoma cruzi (Chagas disease).
• Horses:
  • Treatment of atrial fibrillation, supraventricular tachycardia, or ventricular tachycardia.
  • Reported use in cardioversion from atrial fibrillation.
• Cats:
  • Limited published information; not commonly used due to toxicity concerns. Use only in rare cases with extreme caution.
• Other species:
  • Limited data exists for other species; most applications are extrapolated from dogs, cats, and horses.

Dose of Amiodarone 

Dose of Amiodarone In Dogs:

• Oral:
  • Loading dose: 10–15 mg/kg p.o. q12h for 7 days.
  • Intermediate dose: 5–7.5 mg/kg p.o. q12h for 14 days.
  • Maintenance dose: 5–7.5 mg/kg p.o. q24h.
  • Monitor serum levels at 3 weeks after therapy initiation.
• Intravenous:
  • 0.03–0.05 mg/kg/min continuous rate infusion for cardioversion of atrial fibrillation or sustained supraventricular tachycardia.
  • For acute emergencies: 2 mg/kg bolus followed by 0.8 mg/kg/hour continuous rate infusion.

Dose of Amiodarone In Cats:

No Information

Dose of Amiodarone In Horses:

• Oral:
  • 5 mg/kg p.o. q24h, typically reserved for long-term management of arrhythmias.
• Intravenous:
  • Loading dose: 5 mg/kg/hour IV continuous rate infusion for 1 hour.
  • Maintenance dose: 0.83 mg/kg/hour IV continuous rate infusion for 23 hours, then 1.9 mg/kg/hour IV continuous rate infusion for 30 hours.
  • Treatment stops when conversion occurs or if adverse effects develop.

Side Effects of Amiodarone

• Dogs:
  • Bradycardia, AV block, and prolongation of the QT interval.
  • Gastrointestinal disturbances: anorexia, vomiting, and diarrhea.
  • Hepatotoxicity, keratopathy, positive Coombs’ test, and pulmonary fibrosis.
  • IV administration risks: injection site pain, hypotension, and hypersensitivity reactions.
• Cats:
  • Severe gastrointestinal toxicity and hypersensitivity reactions, including anaphylaxis.
• Horses:
  • Hind limb weakness, diarrhea, and elevated bilirubin levels during prolonged IV administration.

Contraindications of Amiodarone

void use in animals with:

• Sinus bradycardia.
• AV block.
• Severe thyroid dysfunction or iodine hypersensitivity.
• Hepatic dysfunction or pre-existing hepatopathy (monitor closely if use is unavoidable).

Some Notes:

• Monitoring:
  • Regular ECG monitoring is essential during amiodarone therapy.
  • Baseline and periodic evaluation of liver enzymes, thyroid function tests, CBC, and thoracic radiographs.
  • For T. cruzi: Monitor therapeutic response with PCR or serology.
• Drug Interactions:
  • Drugs increasing amiodarone levels: Cimetidine, azole antifungals.
  • Drugs affected by amiodarone: Beta-blockers, calcium-channel blockers, digoxin, lidocaine, methotrexate, and warfarin.
  • Increased arrhythmia risk: Antiarrhythmics (procainamide, sotalol), macrolides (azithromycin, erythromycin), fluoroquinolones (moxifloxacin), and opioids (methadone).
• Special considerations:
  • Administer IV amiodarone with an in-line filter and a dedicated central venous catheter.
  • Use Nexterone® to avoid hypersensitivity reactions associated with polysorbate 80-containing formulations.