Character of adverse effects of prophylactic lidocaine in the coronary care unit

Adverse effects of lidocaine therapy for proved or suspected myocardial infarction were evaluated for 48 hours in 285 patients arriving at the hospital within 6 hours of the onset of chest pain. More adverse effects occurred in patients receiving lidocaine (51%) than in those receiving placebo (16%; P < 0.0001). Patients receiving lidocaine had more adverse effects in the first 12 hours as compared with the second 12 hours (50% vs. 19%; P < 0.001). Patients without infarction who received lidocaine had more adverse effects than similarly dosed patients with infarction (64% vs. 39%; P = 0.002). The proportion of major adverse effects in those patients having any adverse effect was much greater in the last 24 hours as compared with the first 24 hours (86% vs. 32%; P = 0.006). All life-threatening problems (n = 5) occurred in the first 24 hours, most frequently in the first hour. Lidocaine levels were only weakly related to adverse effects potentially caused by lidocame toxicity. We conclude that the adverse effects of prophylactic lidocaine have been understated in the past and may negate its antiarrhythmic efficacy.