Monoamine Oxidase Inhibitor (MAOI) Toxicity Clinical Presentation

Updated: Oct 25, 2023
  • Author: Eddie Garcia, MD; Chief Editor: Michael A Miller, MD  more...
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The patient history is of vital importance to the diagnosis of monoamine oxidase inhibitor (MAOI) toxicity. Because many of the signs and symptoms are nonspecific, a careful history of all prescription medications, over-the-counter drugs, supplements, and dietary items must be obtained. Additionally, because the effects of many MAOIs (including all of the ones available in the United States) are irreversible and restoration of MAO activity takes 2-3 weeks, [6] , a history of past medications should be obtained as well.

The most common MAOIs are phenelzine, tranylcypromine, isocarboxazid, and selegiline. Reversible inhibitors of MAO are available in Europe (eg, brofaromine, cimoxatone, clorgyline, lazabemide, moclobemide). Other common agents that have MAOI-like activity and have been reported to cause serotonin syndrome include St. John's wort, methylene blue, and linezolid. [15, 16, 17, 18, 25]

In many cases, a significant latent period occurs between exposure and the maximal of clinical effects. Early mild symptoms include irritability, anxiety, flushing, sweating, and headache. As the episode continues, a patient may complain of fever, agitation, diplopia, and restlessness. If the toxicity progresses further, severe symptoms include seizures, confusion, hallucinations, altered mental status, and coma.

As with any ingestion, the possibility of self-harm exists and a detailed psychiatric history should be taken as well.


Physical Examination

Patients with MAOI overdoses or interactions present with excessive catecholamine stimulation toxidromes. Late in the course, the patient may become hypotensive and comatose. Clinical manifestations can be classified into mild, moderate, and severe.

A peculiar nystagmus has been reported in cases of overdose. Rapid jerking movement of the eyes as if watching a tennis or ping pong match—termed "ping pong gaze" [26, 27] or opsoclonus—has been reported in severe MAOI intoxication.

Mild signs include agitation, diaphoresis, tachycardia, and mild temperature elevation. Signs of moderate toxicity include altered mental status, tachypnea, vomiting, dysrhythmias, hyperthermia, and hypertension, which can be critically severe and precipitate rhabdomyolysis, myocardial infarction, intracranial hemorrhage, renal failure, and other hypertensive emergency complications.

Severe signs include the following:

  • Severe hyperthermia (> 106° F)
  • Seizures
  • CNS depression
  • Coma
  • Cardiorespiratory depression
  • Muscle rigidity
  • Myoclonus