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Mesantoin (Mephenytoin) - Side Effects and Adverse Reactions



A number of side effects and toxic reactions have been reported with Mesantoin® (mephenytoin) as well as with other hydantoin compounds. Many of these appear to be dose related while others seem to be a manifestation of a hypersensitivity reaction to these drugs.

Blood Dyscrasias

Leukopenia, neutropenia, agranulocytosis, thrombocytopenia and pancytopenia have occurred. Eosinophilia, monocytosis, and leukocytosis have been described. Simple anemia, hemolytic anemia, megaloblastic anemia and aplastic anemia have occurred but are uncommon. There has been an isolated report of lymphoma in the literature in a patient treated with mephenytoin for 17 years; a drug relationship has not been defined.

Skin and Mucous Membrane Manifestations

Maculopapular, morbilliform, scarlatiniform, urticarial, purpuric (associated with thrombocytopenia) and non-specific skin rashes have been reported. Exfoliative dermatitis, erythema multiforme (Stevens-Johnson Syndrome), toxic epidermal necrolysis and fatal dermatitides have been described on rare occasions. Skin pigmentation and rashes associated with a lupus erythematosus syndrome have also been reported.

Central Effects

Drowsiness is dose-related and may be reduced by a reduction in dose. Ataxia, diplopia, nystagmus, dysarthria, fatigue, irritability, choreiform movements, depression, and tremor have been encountered.

Nervousness, nausea, vomiting, sleeplessness and dizziness may occur during the initial stages of therapy. Generally, these symptoms are transient, often disappearing with continued treatment.

Mental confusion and psychotic disturbances and increased seizures have been reported, but a definite causal relationship with the drug is uncertain.


Hepatitis, jaundice and nephrosis have been reported but a definite cause and effect relationship between the drug and these effects has not been established.

Alopecia, weight gain, edema, photophobia, conjunctivitis, and gum hyperplasia have been encountered.

Polyarthropathy, pulmonary fibrosis, lupus erythematosus syndrome, lymphoma and lymphadenopathy which simulates Hodgkin’s Disease have also been observed.

Drug label data at the top of this Page last updated: 2006-04-07

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