TCA poisoning

Q: Sodium bicarbonate is indicated in patients with Tricyclic Antidepressants (TCA) poisoning who develop? 

A) >100 msec 
B) Ventricular arrhythmia
C) Unspecified arrhythmia
D) Unexplained hypotension
E) All of the above


Answer: E

Sodium bicarbonate is the standard of care and recommended initial therapy in TCA toxicity to avoid any cardiac complication. It is cheap, effective and easy to institute. Interestingly, even if widened QRS interval does not show narrowing on EKG, sodium bicarbonate infusion is recommended to be continued, as lower serum pH potentiates the poisoning of TCA. Recommended target pH is 7.50 to 7.55. High serum pH favors the non-ionized form of the drug, making it less available to bind to sodium channels. Also, increase extracellular sodium concentration increases the electrochemical gradient across myocardium cell membrane, attenuating the TCA-induced blockade of rapid sodium channels.

#toxicology
#cardiology


References:

1. Hoffman JR, Votey SR, Bayer M, Silver L. Effect of hypertonic sodium bicarbonate in the treatment of moderate-to-severe cyclic antidepressant overdose. Am J Emerg Med 1993; 11:336. 

2. Bruccoleri RE, Burns MM. A Literature Review of the Use of Sodium Bicarbonate for the Treatment of QRS Widening. J Med Toxicol 2016; 12:121.