Safe and efficacious dosage of flecainide acetate for treating equine atrial fibrillation.
To determine a safe and efficacious dose of flecainide acetate for treating equine atrial fibrillation (Af), the safe dosage level was determined by injecting 1, 2, or 3 mg/kg i.v. of 1% flecainide acetate solution at a rate of 0.2 mg/kg/min to five clinically healthy horses. Clinical signs and the ECG were monitored (HR, PR, QRS, and QT intervals) and blood was taken to measure the plasma flecainide concentration pre- and post-administration. No abnormal signs were observed in the 1- or 2-mg/kg groups, while agitation was observed in three of five horses in the 3-mg/kg group. The QRS, and QT intervals for the 3-mg/kg group increased significantly. The peak plasma flecainide concentrations were 1.316 +/- 358 (SD) ng/ml, 1,904 +/- 314 ng/ml, and 2,251 +/- 387 ng/ml for the 1-, 2-, and 3-mg/kg groups, respectively. To evaluate the efficacy of flecainide, Af was induced by right atrial pacing in six clinically healthy horses, and 1% flecainide acetate solution was then administered until they converted to sinus rhythm. All horses with induced Af converted. For the conversion, a total dose of 1.40 +/- 0.63 mg/kg flecainide was required, the duration of administration was 7.00 +/- 3.15 min and plasma flecainide concentration at conversion was 1,303 +/- 566 ng/ml. In conclusion, flecainide acetate is a safe and effective antiarrhythmic agent for equine Af, and the clinically effective dosage is 1 to 2 mg/kg.
Ohmura
H
H
Racehorse Clinic, Japan Racing Association Miho Training Center, Inashiki-gun, Ibaraki.
Nukada
T
T
Mizuno
Y
Y
Yamaya
Y
Y
Nakayama
T
T
Amada
A
A
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000188:drug therapy / Q000662:veterinary*; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography / Q000187:drug effects / Q000662:veterinary*; D005260:Female; D005424:Flecainide / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D006339:Heart Rate / Q000187:drug effects*; D006734:Horse Diseases / Q000188:drug therapy*; D006736:Horses; D007275:Injections, Intravenous; D008297:Male; D012449:Safety; D012727:Sex Characteristics
D000889:Anti-Arrhythmia Agents; D005424:Flecainide