Lidocaine is a substance administered intravenous in the treatment of ventricular arrhythmias, is generally very well tolerated. The major side effects primarily involve the central nervous system, the cardiovascular system, and the gastrointestinal tract.


The most common adverse effect of lidocaine is central nervous system (CNS) toxicity. The symptoms are usually mild, dose-dependent, and always resolve with a decrease in the infusion rate or discontinuation of the drug. These side effects may be particularly frequent in the elderly or in those with heart failure, settings in which CNS levels are increased due to a reduced volume of distribution, and in patients with significant liver impairment in whom the metabolism of lidocaine is reduced. Tremor is a useful bedside sign of toxicity. Other neurologic side effects include insomnia or drowsiness, lightheadedness, dysarthria and slurred speech, ataxia, depression, agitation, change in sensorium, a change in personality, nystagmus, hallucinations, memory impairment, and emotional lability. High plasma concentrations of lidocaine can also provoke seizures that are usually generalized. This can also occur at lower drug concentrations if lidocaine is given to patients receiving oral tocainide or mexiletine, which are congeners of lidocaine.


Cardiac side effects are an infrequent complication of lidocaine therapy which is generally well tolerated even by patients with significant underlying heart disease. The primary cardiovascular side effects include sinus slowing, asystole, hypotension, and shock. These problems are most commonly related with high dosing or with the overly rapid administration of lidocaine and those who are with preexisting cardio diseases are at high risk.