Lidocaine toxicity

Q: Which of the following can be an earliest sign of  intravenous (IV) lidocaine infusion toxicity? 

 A) Tremor 
 B) Sinus slowing 
C) Hypotension 
D) Increase in the threshold of an implantable cardioverter-defibrillator (AICD) 
E) Nausea and vomiting


Answer:  A

Objective of the above question is to emphasize that lidocaine's earliest signs of toxicity is central nervous system (CNS) based instead of cardio-vascular (CVS) based. They are mostly age and dose-dependent, and at the level of liver insufficiency. Interestingly, and often ignored earliest sign of lidocaine toxicity is tremor. Also sleep disturbance, lightheadedness, slurred speech, delirium and in worse cases seizure may occur.

 CVS side-effects may occur but less likely than CNS side-effects. Lidocaine has shown to increase the defibrillation threshold of AICDs, but this effect may not be significant at clinical level.

 Gastrointestinal (GI) toxicities are not different from any other medications.

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#pharmacology
#cardiology
#toxicology


References:

Rademaker AW, Kellen J, Tam YK, Wyse DG. Character of adverse effects of prophylactic lidocaine in the coronary care unit. Clin Pharmacol Ther 1986; 40:71. 

Lown B, Vassaux C. Lidocaine in acute myocardial infarction. Am Heart J 1968; 76:586. 

Pfeifer HJ, Greenblatt DJ, Koch-Weser J. Clinical use and toxicity of intravenous lidocaine. A report from the Boston Collaborative Drug Surveillance Program. Am Heart J 1976; 92:168. 

Schumacher RR, Lieberson AD, Childress RH, Williams JF Jr. Hemodynamic effects of lidocaine in patients with heart disease. Circulation 1968; 37:965. 

Dorian P, Fain ES, Davy JM, Winkle RA. Lidocaine causes a reversible, concentration-dependent increase in defibrillation energy requirements. J Am Coll Cardiol 1986; 8:327.