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Toxicity, Antidepressant: Differential Diagnoses & Workup
Updated: Nov 13, 2008
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
Other Problems to Be Considered
Antimalarial toxicity (eg, chloroquine, primaquine)
Chloral hydrate toxicity
Intrinsic cardiac disease (other causes of conduction disturbances, dysrhythmias, hypotension)
Intrinsic neurologic disease (other causes of seizures, altered mental status)
Workup
Laboratory Studies
- Quantitative screening or tricyclic serum concentrations are of minimal utility in the acute setting because serum levels do not correlate with acute toxicity secondary to pharmacologic properties such as large volume of distribution, pH-dependent protein binding, wide intrapatient variability of terminal elimination half-lives, and prolonged distribution phases. A toxicology screen may be helpful if concurrent ingestion is possible or if symptoms are not fully explained by tricyclic antidepressants (TCAs). An abbreviated screen for acetaminophen and aspirin coingestants usually is sufficient.
- Electrolytes and glucose levels should be used to screen for anion gap acidosis that exists with other ingestions and to look for metabolic disturbances that can alter mental status, cause seizures, or change the ECG.
- Serum pH
- Blood gas analysis should be obtained to check pH with an attempt to maintain an alkaline environment (pH = 7.45-7.55).
- Acidemia allows a greater degree of fast sodium channel binding by the TCA and produces a wider QRS on the ECG.
Imaging Studies
- Obtain a chest radiograph after intubation or if evidence of hypoxia, aspiration, or ARDS is present.
Other Tests
An ECG has great utility in predicting the severity of toxicity.
- ECG is the single most important test to determine diagnosis and prognosis.
- Several studies have shown that a QRS duration greater than 100 milliseconds on an ECG is associated with an increased incidence of seizures, coma, need for intubation, hypotension, and dysrhythmias.
- Prospective studies of patients with TCA overdose show that the sensitivity of an R-wave greater than 3 mm in aVR is similar to the sensitivity of a QRS=100 msec. Prospective data suggest that the typical period of QRS prolongation after severe tricyclic antidepressant ingestion is 12-18 hours but may be as long as 3 days.
- Rightward deviation of QRS vector (a negative deflection in lead 1 and a positive final deflection in lead aVR) is associated with TCA toxicity.
- Sinus tachycardia is a typical but nonspecific early sign of TCA toxicity.
- Case reports have described ECGs in TCA toxicity mimicking acute myocardial infarction and the Brugada syndrome. One study found that 17% of patients that presented with TCA poisoning and ECG changes had Brugada pattern on ECG, which is a manifestation of intraventricular conduction disturbances.
- Dysrhythmias are also nonspecific to TCA toxicity but important to respond to.
- Ventricular tachycardia is the most common lethal dysrhythmia.
- Torsade de pointes is uncommon in overdose but may occur in patients taking therapeutic doses.
- Bradycardia and asystole are usually preterminal rhythms, although patients have been resuscitated from these with aggressive supportive care.
Procedures
- Endotracheal intubation
- Aggressively manage airway for patients who present agitated or with a decreased level of consciousness. For these patients, endotracheal intubation may be required before gastric lavage or activated charcoal to prevent aspiration.
- The patient should be hyperventilated after intubation. Check proper placement with a chest radiograph. The target PaCO2 is 30 mm Hg by ABG following intubation.
- Gastric lavage
- After the patient's airway, breathing, and circulation are secured, gastric lavage can be initiated in the symptomatic patient with an intentional overdose within 1.5-2 hours after ingestion.
- If the patient exhibits declining mental status, the intubation should be performed first. Activated charcoal should be administered if the benefit of charcoal administration outweighs the risk of aspiration.
- A central venous line may be helpful in administering medication and monitoring fluid status.
- Hemodialysis
- Hemodialysis and hemoperfusion are not effective and are not recommended for TCA poisoning.
- The poor efficacy of hemodialysis probably is because only a small amount of free TCA is present in the serum. TCA is highly bound to serum proteins and tissues, with a large volume of distribution.
- Only anecdotal evidence supports the efficacy of an intra-aortic balloon pump (IABP) for intractable hypotension.
More on Toxicity, Antidepressant |
| Overview: Toxicity, Antidepressant |
 Differential Diagnoses & Workup: Toxicity, Antidepressant |
| Treatment & Medication: Toxicity, Antidepressant |
| Follow-up: Toxicity, Antidepressant |
| Multimedia: Toxicity, Antidepressant |
| References |
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References
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Further Reading
Keywords
antidepressant toxicity, antidepressant overdose, tricyclic antidepressants, TCAs, cyclic antidepressants, antidepressant poisoning, TCA toxicity, TCA overdose, TCA exposure, treatment of depression
