Prediction of efficacy and tolerance of oral mexiletine by intravenous lidocaine application.

In a controlled crossover trial, 15 patients with frequent ventricular arrhythmias were treated with lidocaine to predict efficacy and safety of oral mexiletine. After an initial control period, patients received intravenous lidocaine (bolus infusion of 200 mg/20 min followed by 3.6 gm/24 hr and for 7 days oral mexiletine (200 mg four times a day). Efficacy was controlled by 24-hour Holter monitoring (responders = suppression of single premature ventricular beats [PVB] greater than 84% and of complex PVB greater than 90%). After lidocaine, 10 of 15 patients (67%) were responders (mean PVB reduction: 97%). After mexiletine, five of 15 patients (33%) were responders (mean PVB reduction: 81%); efficacy was closely related to the plasma concentration. When efficacy of both agents was compared, lidocaine infusion had a positive predictive value of only 50%; however, the negative predictive value was 100%. Thus in nonresponders to lidocaine, mexiletine is very likely to fail in the suppression of ventricular ectopy.