This is used as a medication for status epilepticus and is considered a 2nd line agent, used when benzodiazepines fail.
Phenytoin is indicated for treating generalized tonic-clonic (grand mal) seizures, and is considered a 1st line agent.
Phenytoin acts to block Na+ channel activation on the neuronal cell membrane. More specifially, it increases sodium channel inactivation, decreasing the flux of sodium ions across the neuronal membrane. This limits the spread of seizure activity and reducing seizure propagation. It tends to stabilize the threshold against hyperexcitability caused by excessive stimulation or environmental changes.
As a consequence of blocking Na+ channel activation, phenytoin inhibits glutamate release from excitatory presynaptic neurons and enhances GABA release.
Phenytoin, though an anticonvulsant, is also a class IB antiarrhythmic medication.
Phenytoin is known to be a teratogen and causes fetal hydantoin syndrome, which is characterized by intrauterine growth restriction, microcephaly, craniofacial deformities and developmental delay.
Phenytoin decreases folate levels, leading to a macrocytic megaloblastic anemia.
Phenytoin is an inducer of the P450 enzyme responsible for the hepatic degradation of various drugs.
A side effect tied to phenytoin use is drug-induced lupus. This is an autoimmune disease which can be caused by chronic use of certain drugs, including phenytoin. Patients characteristically display anti-histone antibodies.
Chronic use can lead to peripheral neuropathy, while ataxia and diplopia can be seen with acute use of phenytoin.
Hirsutism, which is excessive hair growth in women, is seen with long term use of phenytoin.
Gingival hyperplasia, or gingival overgrowth, is a side effect plaguing up to 50% of patients taking phenytoin for epilepsy.
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