Antiarrhythmic efficacy and safety of oral mexiletine in dogs with ventricular arrhythmias: a multicentre, retrospective analysis.

Abstract

Objective: To describe mexiletine's efficacy in suppressing ventricular arrhythmias (VAs) and its safety in dogs.

Methods: In a multicenter retrospective study, dogs received oral mexiletine, prescribed as a second-line antiarrhythmic in addition to a first-line agent, for the treatment of VA ineffectively controlled by initial monotherapy. Signalment, clinical, diagnostic, therapeutic, and outcome data were retrieved. Only dogs that underwent Holter monitoring both before and after starting mexiletine treatment were included in the ECG analysis of efficacy. This was represented by a reduction in the Lown-Wolf grade < 5 or a reduction in the number of ventricular premature complexes ≥ 85%. Treatment-related side effects (TRSE) were noted in all dogs. Statistical analysis was performed to compare selected data before and after mexiletine prescription.

Results: 38 dogs were included. Twenty dogs met the criteria for the efficacy analysis; mexiletine effectively suppressed VA in 16 of 20 cases (80%). In 11 of 38 dogs (28.9%), TRSE occurred (ie, gastrointestinal and neurological signs in 10 of 11 [90.9%] and 1 of 11 cases [9.1%], respectively). Supportive therapies were prescribed to 10 of 11 dogs (90.9%) and the daily dose of mexiletine was reduced in 6 of 11 dogs (54.5%), resulting in resolution of TRSE in 5 of 11 dogs (45.5%). In the remaining 6 of 11 dogs (54.5%), the persistence of TRSE led to the discontinuation of mexiletine. The median duration of TRSE was 7 days (IQR, 4 to 10 days).

Conclusions: Mexiletine was highly effective in suppressing VA, but reversible gastrointestinal TRSE occurred relatively frequently.

Clinical relevance: Useful information on the effects of mexiletine in dogs with VAs is provided.