To assess the antiarrhythmic effect of
lorcainide and determine whether there is a pharmacokinetic interaction between
lorcainide and
digoxin, 12 patients with frequent premature ventricular depolarizations (PVDs) who were taking
digoxin were treated with
lorcainide. During a placebo period, serum
digoxin concentration was measured for three days; plasma
lorcainide concentration, a 12-lead electrocardiogram (ECG), and a 24-hour continuous ECG were measured on the day before the patients began
lorcainide and repeated on days 3, 7, and 14 of treatment.
Lorcainide was given 100 mg bid or 100 mg tid.
Lorcainide did not suppress group mean PVDs per hour, pairs, or
ventricular tachycardia. Only four patients (33%) responded with greater than or equal to 80% suppression of PVDs. Mean ejection fraction for responders was 46 +/- 6%, and for nonresponders it was 28 +/- 9% (P less than .01). There was no significant pharmacokinetic interaction between
lorcainide and
digoxin. Mean
digoxin concentration did not change after
lorcainide administration; two patients had greater than or equal to 50% increase in serum
digoxin concentration. Patients with
heart failure or reduced ejection fraction define a subset who have unpredictable effects from
lorcainide, including a reduced antiarrhythmic effect.