HWN Suggests

Massive TCA Overdose

Tricyclic anti-depressant (TCAs) medications are not used to the same extent for depression that they once were; there are other indications, and overdose, when seen, is a picture of depressed level of consciousness, seizures, dysrhythmias and hypotension, leading to death. There is no antidote; management is aggressive supportive care with some theoretical reasoning behind strategies chosen.

The important message is that the strategies used to treat the TCA overdose can be extrapolated in many other overdose situations… for the type 1A and 1C anti-dysrhythmics, cocaine, propranolol, anti-psychotics, anti-histamines in large amounts – to name a few.

read full article

Featured

  TCA Overdose: Narrow Windows

Currently, TCAs have been relegated to the treatment of migraines, chronic pain syndromes, insomnia, and other obscure neuropathic/musculoskeletal/somatic disorders. TCA poisoning, while uncommon, remains a life-threatening issue and continues to be a classic, frequently tested topic on exams.

 Cyclobenzaprine vs TCA Toxicity

Fortunately, the one double bond in the central ring of cyclobenzaprine (absent in amitriptyline) makes a world of difference. A single-substance overdose with cyclobenzaprine will share the anticholinergic characteristics with amitriptyline and other TCAs. If large quantities are ingested, providers should expect symptoms consistent with anticholinergic toxicity... While fears of cardiac and neurologic toxicities have been documented because of cyclobenzaprine’s TCA-like structure, these adverse events have not been shown.

 TCA Overdoses and Mimics: Don’t Delay, Don’t Be Led Astray

QRS prolongation and a terminal R’ should raise concern for tricyclic antidepressant (TCA) overdose, a diagnosis that often must be made on EKG alone due to a quick clinical progression and a high mortality rate. In cases of TCA overdose, a QRS greater than 100 ms is predictive of seizures, and as many as 50% of patients with a QRS over 160 ms will experience ventricular arrhythmias.1 TCAs exert their therapeutic effect by inhibiting the reuptake of norepinephrine and serotonin. At toxic doses TCAs also block sodium channels, impeding sodium entry into myocardial cells.

 Tox in The Land: Tricyclic Antidepressants

TCAs have a ton of MOA leading to a variety of uses and presentations when toxicity develops...

 Vicious Cycles: Management of the Tricyclic Antidepressant Overdose

The ECG is the best predictor of the clinical course in TCA Overdose, as opposed to drug levels. In one study, QRS width > 100 ms carried a 33% risk of seizures, and QRS > 160 ms carried a 50% risk of dysrhythmias. No seizures or dysrhythmias occured below these respective thresholds.​

Articles of Interest

How did physostigmine get a bad rap?

Today physostigmine is contraindicated in TCA poisoning. But if we think about it, physostigmine administration probably wasn’t a good idea in the first place. Correcting anticholinergic toxicity of TCA has limited benefit; mortality from TCA overdose is usually associated with cardiac toxicity (Na-channel blockade) and should be treated with NaHCO3 administration Physostigmine still has a role in treating isolated anticholinergic toxicity (e.g. diphenhydramine, benztropine, dimenhydrinate, scopolamine, jimson weed overdose).

#SimBlog: Tricyclic Antidepressant Overdose

Consider Sodium Bicarb, magnesium and intralipid for TCA overdose.

Back to Basics: TCA Toxicity - EKG Findings

PR prolongation/AV-block (p-waves often buried)...

CORE EM: Tricyclic Antidepressant Toxicity

Sodium Bicarbonate (NaHCO3): Bolus 1-2mEq/kg with additional boluses every 3-5 minutes until the QRS narrows to <100ms and hypotension improves.

Specific antidotes: the role of sodium bicarbonate in tricyclic overdose

The indication for the use of bicarbonate in tricyclic overdose is the widening of the QRS interval, rather than the metabolic acidosis (which may or may not accompany TCA poisoning). Exactly how this works is a topic of some debate.

TCA toxicity

This is your one stop page for TCA overdose. Find out how to manage the acute overdose and the potential complications. We have also covered the basic TCA pharmacology and a tutorial about sodium channel blockade and the ECG, find out why the QRS will widen.

ToxCard: TCA Poisoning

TCAs are sodium channel blockers and primary treatment of TCA poisoning is sodium bicarb. The EKG abnormalities like QRS≥100, R wave in avR ≥3mm, and R/S> 0.7 can predict significant toxicity. Sodium bicarb displaces the TCA from the Na binding site by raising the Na+ gradient and increasing the pH. Prolonged resuscitation might be necessary.

Tricyclic Antidepressant Overdose

TCAs are highly toxic in overdose, the most severe effects being cardiovascular and neurological instability. They have a narrow therapeutic window, with toxicity seen even with lower doses. The clinical presentation can vary depending on severity. The clinical manifestations of overdose become apparent within six hours of ingestion. The key clinical features of TCA overdose include signs of anticholinergic toxicity and the result of sodium channel blockade. Severe effects include arrhythmia, cardiovascular collapse, convulsions and coma.

Resources

EM in 5

Dominant r wave in AVR...

EM Sim Cases

Although largely replaced by newer and safer agents for the treatment of depression, tricyclic antidepressants are still routinely prescribed, especially for chronic pain. This case highlights three important aspects of the management of a tricyclic overdose:

Maimonides Emergency Medicine

QRS > 100 ms is predictive of seizures, QRS > 160 ms is predictive of ventricular arrhythmias (e.g. VT).

Kings County EM

ABC’s first… Intubation, Supplemental O2, Crystalloid, Get an EKG – If QRS > 100 msec —intravenous sodium bicarbonate (for sodium load), If pressors needed, use NE or neosynephrine, If patient develops Torsades, treat w/ MgSO4.

BC Emergency Medicine Network

Acute ingestion of > 5 mg/kg of most tricyclics may result in toxicity.

StatPearls

In adults, TCAs are also used for migraine headache prophylaxis, treatment of neuralgic pain, including the pain associated with Ciguatera poisoning, and obsessive-compulsive disorder. In children, TCAs have been used to treat nocturnal enuresis. Despite the current limited use of TCAs, TCA-overdose-associated hospitalizations and fatalities are on the rise.

WikEM

Activated charcoal 1gm/kg x1 if <1 hour and patient awake and cooperative without signs of toxicity.