[Clinical study evaluated by Holter monitoring and by mexiletine serum levels in ventricular arrhythmias].

Three normal individuals and 17 cardiac patients with frequent VPBs were given mexiletine orally for 5 days (400-1000 mg daily in two to five doses). Each patient was evaluated by means of 24-hour Holter monitoring before treatment, on the fifth day and 4 days after the drug was discontinued. In 15 patients mexiletine serum levels were measured before and 2 hours after the first dose given in the morning. Urinary pH was also measured. VPBs were reduced by an average of 67.6%; in 11 patients the VPBs decreased by 92.3%. After treatment was discontinued, VPBs increased by 2.6%. Serum levels of the drug were generally within the therapeutic range (1.05 +/- 0.39 mcg/ml). We conclude that mexiletine is effective in reducing the number of VPBs; Holter monitoring and serum level measurements are both clinically helpful.