Monoamine Oxidase Inhibitor Overdose

Key Features

• Potential food or drug interactions can occur during therapeutic use

• Ingestion of tyramine-containing foods (eg, aged cheese and red wines) or any sympathomimetic drug may cause a severe hypertensive reaction

• Severe or fatal hyperthermia (serotonin syndrome)

  • May occur when monoamine oxidase inhibitors (MAOIs) are given with serotonin-enhancing drugs (eg, meperidine, fluoxetine, paroxetine, fluvoxamine, venlafaxine, tryptophan, dextromethorphan, tramadol)

  • Can also occur with moclobemide (an MAOI not available in the United States) and linezolid, which has MAOI properties

  • Can also occur with selective serotonin reuptake inhibitors (SSRIs) in large doses or in combination with other SSRIs, even in the absence of an MAOI or meperidine

Clinical Findings

• Acute overdose

  • Ataxia, excitement, hypertension, and tachycardia

  • Several hours later: hypotension, convulsions, and hyperthermia

• Food or drug hypertensive reaction

  • Hypertension

  • Tachycardia

  • Headache

  • Possible intracranial hemorrhage

• Serotonin syndrome

  • Fever

  • Agitation

  • Delirium

  • Diaphoresis

  • Hyperreflexia

  • Clonus (spontaneous, inducible, ocular)

  • Hyperthermia (can be life-threatening)

Diagnosis

• Serum drug levels are not available nor useful

• Generally not detected on urine toxicology screens

Treatment

• Acute overdose

  • Administer activated charcoal, 60–100 g orally or via gastric tube, mixed in aqueous slurry if ingestion is within 1

  • Treat hypotension with fluids and positioning, but avoid use of pressor agents if possible

  • Treat severe hypertension with nitroprusside, phentolamine, or other rapid-acting vasodilators

• Serotonin syndrome

  • Cyproheptadine, 4 mg orally (or by gastric tube) every hour for three or four doses, or chlorpromazine 25 mg intravenously, can be effective

• Observe patients for at least 24 h because hyperthermia may be delayed (see Hyperthermia)