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29-11-2011 | Article

Amiodarone effective for dogs with ventricular arrhythmias

Abstract

Free abstract

MedWire News: Amiodarone appears to be effective and well-tolerated for the treatment of ventricular arrhythmias in dogs, UK veterinarians report.

The study supports the use of amiodarone in dogs that have failed to respond adequately to standard antiarrhythmic medications, say Jordi López-Alvarez (University of Liverpool) and co-authors.

Dogs with ventricular arrhythmias are traditionally treated with class I, II, or III antiarrhythmic drugs, such as mexiletine, atenolol, or sotalol.

Amiodarone is a class III drug with only minor negative inotropic effects, but also has class I, II, and IV effects. It is widely used in humans to treat ventricular tachycardia and ventricular fibrillation, but is rarely used in veterinary medicine.

In this study, López-Alvarez and team retrospectively searched their unit's database to identify dogs given amiodarone as an antiarrhythmic therapy between 2003 and 2010. A total of 28 cases were found.

The indications for amiodarone included supraventricular arrhythmias in 16 cases and ventricular arrhythmias in 12 cases. The majority of dogs also had chronic heart failure and structural heart disease.

In all cases, standard antiarrhythmic drugs had been tried or were contraindicated. The median loading dose of amiodarone was 22.22 mg/kg/day for 7-14 days followed by a maintenance dose of 6.36 mg/kg/day.

On maintenance therapy, median amiodarone blood levels were 0.8 mg/L, which is within the accepted reference range (0.5-2.0 mg/L). However, median levels of the metabolite, desethylamiodarone, were 0.1 mg/L, which is below-normal based on the human reference range (0.5-2.0 mg/L).

The dogs were re-examined after a median of 27 days (range 7-70 days). Just two of the 28 dogs (7.1%) showed no improvement after starting amiodarone, while three dogs (10.7%) that initially converted to sinus rhythm subsequently developed arrhythmias.

In 17 dogs with heart rate recordings, the mean rate fell from 207 beats per minute (bpm) before amiodarone to 130 bpm after amiodarone. There was no evidence of worsening heart failure or worsening systolic function.

In terms of tolerability, amiodarone was stopped in two dogs due to side effects - specifically, lethargy and gastrointestinal signs in one dog, and lack of efficacy and mildly increased liver enzymes in one dog.

Importantly, however, blood levels of alkaline phosphatase, alanine aminotransferase, thyroxine, and thyroid-stimulating hormone did not change significantly after starting amiodarone therapy.

López-Alvarez et al conclude: "The results of this study suggest that amiodarone is an effective drug for the treatment of supraventricular and ventricular arrhythmias in dogs and in some cases it can be used to convert arrhythmias back to sinus rhythm.

"Therefore, amiodarone might be a safe and effective alternative drug for the treatment of arrhythmias not controlled with commonly used antiarrhythmic drugs and in cases of myocardial dysfunction."

By Joanna Lyford