Monoamine oxidase inhibitors (MAOIs) irreversibly inhibits MAO, an enzyme found in nerves and other tissues (including the liver), to break down the biogenic amines NE, dopamine, and 5HT and relieve depression. At one time, MAOIs were used more often, but now they are used rarely because they require a specific dietary regimen to prevent toxicity. There are some patients, however, who only seem to respond to these particular drugs, so they remain available. Agents still in use include isocarboxazid (Marplan), phenelzine (Nardil), and tranylcypromine (Parnate). The choice of an MAOI depends on the prescriber’s experience and individual response. A patient who does not respond to one MAOI may respond to another.
Blocking the breakdown of the biogenic amines NE, dopamine, and 5HT allows these amines to accumulate in the synaptic cleft and in neuronal storage vesicles, causing increased stimulation of the postsynaptic receptors. It is thought that this increased stimulation of the receptors causes relief of depression. The MAOIs are generally indicated for treatment of the signs and symptoms of depression in patients who cannot tolerate or do not respond to other, safer antidepressants.
The MAOIs are well absorbed from the GI tract, reaching peak levels in 2 to 3 hours. They are metabolized in the liver primarily by acetylation and are excreted in the urine. Patients with liver or renal impairment and those known as “slow acetylators” may require lowered doses to avoid exaggerated effects of the drugs. The MAOIs cross the placenta and enter breast milk.
Drug interactions of MAOIs with other antidepressants include hypertensive crisis, coma, and severe convulsions with TCAs and a potentially life-threatening serotonin syndrome with SSRIs. A period of 6 weeks should elapse after stopping an SSRI before beginning therapy with an MAOI.
If MAOIs are given with other sympathomimetic drugs (e.g., methyldopa, guanethidine), sympathomimetic effects increase. Combinations with insulin or oral antidiabetic agents result in additive hypoglycemic effects. Patients who receive these combinations must be monitored closely, and appropriate dose adjustments should be made.
1. The client diagnosed with panic disorder is taking a phenelzine (Nardil), an MAO inhibitor. Which statement by the client warrants immediate intervention?
A. “I am very careful about what I eat.”
B. “I have been taking Robitussin for my cough.”
C. “I took two Tylenol for my headache.”
D. “I only drink one cup of coffee a day.” 2. The client with major depressive disorder is prescribed the selective serotonin reuptake inhibitor (SSRI) fluoxetine (Prozac). Which intervention should the nurse teach the client concerning this medication?
A. Instruct the client not to eat any type of tyramine-containing foods such as wines or cheeses.
B. Notify the health-care provider if the client becomes anxious or has an elevated temperature.
C. Encourage the client to take the medication with grapefruit juice.
D. Explain that tremors and sweating are initial expected side effects.
1. B. “I have been taking Robitussin for my cough.”
Rationale: Dextromethorphan (Robitussin) interacts with MAOIs to produce hypertension, fever, and coma. This statement warrants intervention. 2. B. Notify the health-care provider if the client becomes anxious or has an elevated temperature.
Rationale: Serotonin syndrome (SES) is a serious complication of SSRIs that produces mental changes (confusion, anxiety, and restlessness), hypertension, tremors, sweating, hyperpyrexia (elevated temperature), and ataxia. Conservative treatment includes stopping the SSRI and using supportive treatment. If untreated, it can lead to death.
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