Plasma levels of lidocaine after intramuscular injection and subsequent infusion in patients with acute myocardial infarction.

It has been proposed that prophylactic administration of lidocaine i.m. can prevent ventricular arrhythmias during myocardial infarction. Thus we studied the pharmacokinetics of lidocaine after i.m. injection of 300 mg in the deltoid muscle and subsequent infusion to maintain antiarrhythmically effective plasma levels. The mean duration for exceeding a threshold concentration of 1.5 mg/l after 300 mg lidocaine i.m. was about 2 h; maximum concentrations were reached after 10 min and amounted to 3.2 mg/l (n = 10). By varying the infusion onset after i.m. injection (1 or 2 h later) and the infusion rates from 0.029-0.039 mg/kg X min, steady-state plasma levels of lidocaine were found to be in the therapeutic range (1.5-6 mg/l) for 5 h of observation. Long-lasting infusions (greater than 10 h) may result in increased plasma concentrations of lidocaine due to reduced body clearance.