Review Question - QID 206924

This patient's clinical presentation is most consistent with an overdose of a tricyclic antidepressant (TCA), like amitriptyline.

TCA toxicity is characterized by "The 3 C's": convulsions, coma, and cardiotoxicity. Cardiotoxicity usually manifests as a prolonged QT interval on EKG, and this finding is the best indication of TCA overdose. In addition, symptoms of anticholinergic toxicity (urinary retention, dry mouth etc.) are also present. Patients presenting with TCA overdose should be treated with sodium bicarbonate, which lessens the cardiotoxicity and also improves renal excretion of TCAs. Of note, patients with a high risk of suicide should not be prescribed TCAs, because lethal toxicity can result from significantly lower doses than other antidepressants.

Adams et al. discuss the pharmacologic treatment of depression. In addition to coma, convulsions, and cardiotoxicty, they note that respiratory depression and hypothermia can also result from TCA overdose. Given the severe toxicity profile of TCA overdose, they suggest that selective serotonin uptake inhibitors may be a better option for treatment of depression in patients who have a high risk of suicide.

Agarwala et al. discuss the administration of lipid emulsions for treatment of TCA overdose. Lipid emulsions have gained momentum as treatment for overdose of other lipophilic medications, and several reports have shown efficacy for TCA overdose. Agarwala et al. present a case in which a lipid infusion was given instead of oral, high-dose lipids, and the patient was also treated successfully.

Illustration A is a chart showing the features of serotonin syndrome (which can be caused by TCAs), neuroleptic malignant syndrome (most commonly caused by typical antipsychotics), anticholinergic toxicity, and malignant hyperthermia.

Incorrect Answers:
Answer 2: Sertraline overdose is characterized by rigidity, hyperreflexia, autonomic hyperactivity, and hallucinations, which are symptoms of serotonin syndrome.
Answer 3: Bupropion overdose is rarely lethal. Symptoms typically include aggressive behavior, hallucinations, and seizures.
Answer 4: Venlafaxine overdose is rarely lethal. Symptoms typically include serotonin syndrome, seizures, and vomiting.
Answer 5: Fluoxetine overdose is is characterized by rigidity, hyperreflexia, autonomic hyperactivity, and hallucinations, which are symptoms of serotonin syndrome.