Phenelzine sulfate is a potent inhibitor of monoamine oxidase. Because this enzyme is widely distributed throughout the body, diverse pharmacologic effects can be expected to occur. When they occur, such effects tend to be mild or moderate in severity (see below), often subside as treatment continues, and can be minimized by adjusting dosage; rarely is it necessary to institute counteracting measures or to discontinue phenelzine sulfate.
Common side effects include:
Nervous System—Dizziness, headache, drowsiness, sleep disturbances (including insomnia and hypersomnia), fatigue, weakness, tremors, twitching, myoclonic movements, hyperreflexia.
Gastrointestinal—Constipation, dry mouth, gastrointestinal disturbances, elevated serum transaminases (without accompanying signs and symptoms).
Cardiovascular—Postural hypotension, edema.
Genitourinary—Sexual disturbances, eg, anorgasmia and ejaculatory disturbances and impotence.
Less common mild to moderate side effects (some of which have been reported in a single patient or by a single physician) include:
Nervous System—Jitteriness, palilalia, euphoria, nystagmus, paresthesias.
Dermatologic—Pruritus, skin rash, sweating.
Special Senses—Blurred vision, glaucoma.
Although reported less frequently, and sometimes only once, additional severe side effects include:
Nervous System—Ataxia, shock-like coma, toxic delirium, manic reaction, convulsions, acute anxiety reaction, precipitation of schizophrenia, transient respiratory and cardiovascular depression following ECT.
Gastrointestinal—To date, fatal progressive necrotizing hepatocellular damage has been reported in very few patients. Reversible jaundice.
Metabolic—Hypermetabolic syndrome (which may include, but is not limited to, hyperpyrexia, tachycardia, tachypnea, muscular rigidity, elevated CK levels, metabolic acidosis, hypoxia, coma and may resemble an overdose).
Respiratory—Edema of the glottis.
General—Fever associated with increased muscle tone.
Withdrawal may be associated with nausea, vomiting, and malaise.
An uncommon withdrawal syndrome following abrupt withdrawal of phenelzine sulfate has been infrequently reported. Signs and symptoms of this syndrome generally commence 24 to 72 hours after drug discontinuation and may range from vivid nightmares with agitation to frank psychosis and convulsions. This syndrome generally responds to reinstitution of low-dose phenelzine sulfate therapy followed by cautious downward titration and discontinuation.