Updated: Jan 23, 2008
The increased use of antidepressants with safer toxicologic profiles has made monoamine oxidase inhibitor (MAOI) poisoning uncommon among children. MAOIs are still used in patients with Parkinson disease and refractory and atypical depression. Antibiotics, such as the anti– methicillin-resistant Staphylococcus aureus drug linezolid, are MAOIs. Although MAOI ingestion is rare, MAOI overdoses can potentially cause significant morbidity and mortality.1
Monoamine oxidase is a mitochondrial enzyme that functions to deaminate primary and secondary aromatic amines. The deamination of aromatic amines (eg, norepinephrine) leads to the compounds deactivation. MAOIs prevent the breakdown of aromatic amines in the neuronal cytosol, resulting in the storage of larger concentrations of active aromatic amines in neuronal vesicles and, therefore, an increased release of these neurotransmitters into the synaptic cleft with each action potential.
Two types of monoamine oxidases are recognized: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). MAO-A preferentially deaminates norepinephrine and serotonin, whereas MAO-B mainly deaminates phenylethylamine and dopamine. MAO-A inhibitors increase the levels of norepinephrine and serotonin and are used in the treatment of clinical depression. MAO-B inhibitors increase the dopaminergic concentrations in the brain and have been successfully used in the treatment of Parkinson disease.2
Many drugs and foods can potentiate the adrenergic and serotonergic effects of MAOIs. This characteristic is particularly important because many adverse affects involving MAOIs are due to drug-drug and drug-food interactions.3
Commonly used nonselective general MAOIs include phenelzine, isocarboxazid, and tranylcypromine. MAO-A specific inhibitors include moclobemide and clorgyline. MAO-B inhibitors include pargyline and selegiline. The selegiline transdermal system has been used to decrease the risk of a hypertensive crisis.MAOIs overdoses are relatively uncommon. According to the American Association of Poison Control Centers' Toxic Exposures Surveillance System (AAPCC-TESS), 285 MAOI exposures were reported in 2003. Of those exposures, 35 were in patients aged 19 years or younger, and 32 were in patients younger than 6 years.
Most unintentional ingestions occur in toddlers, and most pediatric intentional ingestions occur in adolescents.
Monoamine oxidase inhibitors (MAOIs) are not typically prescribed to children; they are prescribed to adults in a household. Therefore, as in all suspected pediatric ingestions, inquiring about all drugs in the home and evaluating each as a possible cause of the child’s presentation is essential.
MAOIs may not produce symptoms for as long as 24 hours after an acute overdose. Symptoms can be attributed to various physiologic derangements, as follows:
Signs of MAOI overdoses depend on the quantity ingested, the time elapsed since the ingestion, and the presence of co-ingestions.
Signs and symptoms depend on the time of presentation and whether a co-ingestion occurred. The mechanisms for MAOI-related toxicity can be divided into those related to MAOI overdose alone and those related to MAOI interactions with other substances.
| Adrenal Insufficiency | Status Epilepticus |
| Diabetic Ketoacidosis | Thyroid Storm |
| Meningitis, Bacterial | Toxicity, Deadly in a Single Dose |
| Neuroleptic Malignant Syndrome | Toxicity, Iron |
| Pheochromocytoma | |
| Sepsis |
Ethanol withdrawal
Malignant hyperthermia
Sedative/hypnotic withdrawal
Serotonin syndrome
Heat stroke/heat exhaustion
As with most toxic ingestions, the cornerstone of management is continuous monitoring, decontamination when clinically indicated, and meticulous supportive care.
Consider activated charcoal decontamination in any patient who presents within one hour of the ingestion. Activated charcoal is used for drug adsorption and may be sufficient in mild-to-moderate toxicity. It is not absorbed and is excreted entirely through the GI tract.
Emergency treatment in drug or chemical poisoning. Network of pores adsorbs 100-1000 mg of drug per gram of charcoal, decreasing GI absorption of the poison. Does not dissolve in water. In an acute overdose, most effective if given within 1 h of ingestion.
50-100 g PO (1 g/kg) or 10 times amount of ingested poison; administer as susp in 4-8 oz of water
1 g/kg PO administered with water as a slurry
May inactivate ipecac syrup if used concomitantly; decreases effectiveness of coadministered medications; do not mix with sherbet, milk, or ice cream (decreases adsorptive properties)
Documented hypersensitivity; poisoning or mineral acid or alkali overdose
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Not effective in ethanol, methanol, or iron salt poisoning; monitor airway reflexes, neurologic parameters, and bowel sounds
Sympathomimetics produce direct or indirect stimulation of adrenergic receptors and have various actions depending on the specific receptors involved. Stimulation of alpha1-receptors produces smooth muscle contraction. In the cardiovascular system, this effect leads to vasoconstriction and increased blood pressure; in the eye, this effect leads to mydriasis. Other affected organs include the urinary sphincter and uterus. Stimulation of beta1-receptors has an inotropic effect and also increases the heart rate. Stimulation of beta2-receptors leads to smooth muscle relaxation and produces vasodilatation.
Hypotension is initially treated with isotonic fluids. Vasoactive agents are used if hypotension remains refractory despite the administration of intravenous fluids. Norepinephrine is preferred to dopamine because dopamine is an indirect sympathomimetic and can cause an uncontrollable and erratic release of norepinephrine.
Used to treat protracted hypotension after adequate fluid-volume replacement. Stimulates beta1- and alpha-adrenergic receptors, which in turn increase cardiac muscle contractility, heart rate, and vasoconstriction. As a result, systemic blood pressure and coronary blood-flow increase.
0.5-30 mcg/min IV infusion; titrate to effect
0.05-1 mcg/kg/min IV infusion; titrate to effect
In MAOI poisoning, effects can be potentiated; start at low doses; effects increase with concurrent tricyclic antidepressants, MAOIs, antihistamines, guanethidine, methyldopa, or ergot alkaloids; atropine may block reflex tachycardia caused by norepinephrine and enhances pressor response
Documented hypersensitivity; peripheral or mesenteric vascular thrombosis because ischemia may be increased and area of infarct extended
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
If possible, correct blood-volume depletion before administration; administer into large vein because extravasation can cause severe tissue necrosis; caution in occlusive vascular disease
Do not use these drugs routinely. Often, the hypertension is transient and clinically insignificant. Avoid administering pure beta-blockers because they can produce an unopposed alpha effect.
Allows control of hypertensive emergency with rapid onset and short duration. Used as continuous infusion in closely monitored setting (ie, arterial access in pediatric ICU). Produces vasodilation and increases inotropic activity of the heart. At higher doses. May exacerbate myocardial ischemia by increasing heart rate.
0.1-8 mcg/kg/min IV infusion; titrate to effect
Administer as in adults
Effects additive when administered with other hypotensive agents
Documented hypersensitivity; idiopathic hypertrophic subaortic stenosis and atrial fibrillation or flutter
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Use only after euvolemia established; caution in increased intracranial pressure, hepatic failure, severe renal impairment, or hypothyroidism; caution in cerebrovascular disease or coronary artery disease; in renal or hepatic insufficiency, levels may increase and can cause cyanide toxicity; can lower blood pressure and thus should be used only if mean arterial pressure >70 mm Hg
Blocks beta1-, alpha-, and beta2-adrenergic receptor sites, decreasing blood pressure.
20-30 mg IV over 2 min, followed by 40-80 mg q10min; alternately, start continuous infusion at 2 mg/min until blood pressure controlled; not to exceed 300 mg/dose
0.2-0.5 mg/kg/dose IV; not to exceed 20 mg/dose or continuous infusion of 0.25-1.5 mg/kg/h
Decreases effect of diuretics and increases toxicity of methotrexate, lithium, and salicylates; cimetidine may increase blood levels; glutethimide may decrease effects by inducing microsomal enzymes
Documented hypersensitivity; cardiogenic shock, pulmonary edema, bradycardia, atrioventricular block, uncompensated congestive heart failure, reactive airway disease, and severe bradycardia
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in impaired hepatic function; discontinue if signs of liver dysfunction present
Alpha1- and alpha2-adrenergic blocker that blocks circulating epinephrine and norepinephrine action, reducing hypertension that results from catecholamine effects on the alpha-receptors.
1-5 mg IV bolus, repeat q10-15min prn
0.02-0.1 mg/kg IV bolus, may repeat q10-15min prn; not to exceed 5 mg/dose
Concurrent epinephrine or ephedrine may decrease effects; ethanol increases toxicity
Documented hypersensitivity; coronary or cerebral arteriosclerosis and renal impairment
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in tachycardia, peptic ulcer, and gastritis; cerebrovascular occlusions and myocardial infarctions can occur
These agents are used to prevent seizures and terminate clinical and electrical seizure activity.
Benzodiazepines can be used to treat agitation, seizures, or muscle rigidity.
2 mg IV, slowly over 2 min
0.1 mg/kg IV; not to exceed 2 mg/dose; may be repeated
Probenecid and valproic acid increase concentration (may need to reduce dose); theophylline can reverse sedative effects
Documented hypersensitivity
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
May need to adjust dose in hepatic and renal insufficiency
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monoamine oxidase inhibitor, antidepressant overdose, antidepressant poisoning, antidepressant overdoses, antidepressant poisonings, antidepressant-induced hepatotoxicity, childhood ingestions, MAO antidepressant, MAO antidepressant overdose, MAO antidepressant toxicity, MAO antidepressant poisoning, MAOI, MAOIs, MAOI overdose, MAOI toxicity, MAOI poisoning, monoamine oxidase A, MAO-A, monoamine oxidase B, MAO-B, phenelzine, tranylcypromine, isocarboxazid, Parkinson disease, methicillin-resistant Staphylococcus aureus, hypertension, tachycardia, hyperpexia, mydriasis, diaphoresis, rhabdomyolysis, renal failure, pulmonary edema, myocardial infarction, disseminated intravascular coagulopathy, serotonin syndrome
Soumya Ganapathy, MD, Consulting Staff, Department of Emergency Medicine, Union Memorial Hospital
Soumya Ganapathy, MD is a member of the following medical societies: American College of Emergency Physicians
Disclosure: Nothing to disclose.
Frank A Maffei, MD, FAAP, Associate Professor of Pediatrics, Temple University School of Medicine; Director of Medical Student Affairs, Geisinger Health System; Pediatric Critical Care Attending Physician, Janet Weis Children's Hospital at Geisinger Medical Center
Frank A Maffei, MD, FAAP is a member of the following medical societies: American Academy of Pediatrics
Disclosure: Nothing to disclose.
Michael E Mullins, MD, Assistant Professor, Department of Emergency Medicine, Washington University School of Medicine
Michael E Mullins, MD is a member of the following medical societies: American Academy of Clinical Toxicology and American College of Emergency Physicians
Disclosure: Nothing to disclose.
Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc
Disclosure: Pfizer Inc Stock Investment from broker recommendation; Avanir Pharma Stock Investment from broker recommendation
Jeffrey R Tucker, MD, Assistant Professor, Department of Pediatrics, Division of Emergency Medicine, University of Connecticut and Connecticut Children's Medical Center
Jeffrey R Tucker, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Pediatrics, and Massachusetts Medical Society
Disclosure: Nothing to disclose.
Paul D Petry, DO, FACOP, FAAP, Clinical Assistant Professor of Pediatrics, University of North Dakota, School of Medicine and Health Sciences; Consulting Staff, Altru Health System
Paul D Petry, DO, FACOP, FAAP is a member of the following medical societies: American Academy of Osteopathy, American Academy of Pediatrics, American College of Osteopathic Pediatricians, and American Osteopathic Association
Disclosure: Nothing to disclose.
Timothy E Corden, MD, Associate Professor of Pediatrics, Co-Director, Policy Core, Injury Research Center, Medical College of Wisconsin; Associate Director, PICU, Children's Hospital of Wisconsin
Timothy E Corden, MD is a member of the following medical societies: American Academy of Pediatrics, Phi Beta Kappa, Society of Critical Care Medicine, and Wisconsin Medical Society
Disclosure: Nothing to disclose.
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