Clinical presentation

Monoamine oxidase inhibitor poisoning

The onset of symptoms of MAOI poisoning usually occurs 6 to 12 hours after ingestion, but can be delayed up to 24 hours. Symptom onset can occur earlier following acute poisoning in a patient taking long-term MAOI therapy. Symptoms typically last for 1 to 4 days.

The clinical effects of MAOI poisoning are characteristic of serotonergic and sympathomimetic toxidromes, and can be life threatening. The risk of serotonergic toxidrome is high if the patient is taking another serotonergic drug—see Drugs most commonly associated with serotonergic toxidrome for drugs most commonly associated with serotonergic toxidrome.

Early effects of MAOI poisoning include headache, agitation, tremor, sinus tachycardia, mydriasis, hyperreflexia and hyperventilation. As toxicity worsens, hypertension, muscle rigidity, hyperthermia, rhabdomyolysis, clonus and confusion develop. Severe toxicity causes coma, seizures, hypotension, worsening hyperthermia, disseminated intravascular coagulation, life-threatening arrhythmias and cardiac arrest. Death can occur as a result of multiorgan failure.

Tyramine reaction

Tyramine is a dietary amine found in foods such as cheese, wine, preserved meat and yeast products. It is an indirect sympathomimetic that is normally metabolised by intestinal and hepatic monoamine oxidase enzymes. In the presence of a MAOI, excess tyramine can enter the circulation and cause a sympathomimetic toxidrome. Tyramine reactions usually occur within 90 minutes of eating dietary amines, causing severe headache and hypertension. Other sympathomimetic symptoms vary.