Anti-Convulsant Medications

Anticonvulsant : phenytoin, Dilantin

Generic Name: phenytoin
Brand Name(s): Dilantin
Common Use: Anti- convulsant

Phenytoin is an anticonvulsant drug which can be useful in the treatment of epilepsy. The primary site of action appears to be the motor cortex where spread of seizure activity is inhibited. Possibly by promoting sodium efflux from neurons, phenytoin tends to stabilize the threshold against hyperexcitability caused by excessive stimulation or environmental changes capable of reducing membrane sodium gradient. This includes the reduction of posttetanic potentiation at synapses. Loss of posttetanic potentiation prevents cortical seizure foci from detonating adjacent cortical areas. Phenytoin reduces the maximal activity of brain stem centers responsible for the tonic phase of tonic-clonic (grand mal) seizures.

For the control of generalized tonic-clonic and psychomotor (grand mal and temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery.
For the control of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures.
Phenytoin serum level determinations may be necessary for optimal dosage adjustments.
Dilantin with Phenobarbital:
For the control of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures, only in those patients who require both drugs for seizure control and who previously have had their daily anticonvulsant requirements determined by the administration of the two drugs separately. Combinations should not be used to initiate anticonvulsant therapy and are provided as a convenience for epileptic patients.

Contraindications

In those patients who are hypersensitive to phenytoin or other hydantoins.
Phenobarbital is contraindicated in the following conditions: Latent or manifest porphyria or familial history of intermittent porphyria, history of confusion or restlessness from hypnotics, history of abnormal reaction or known hypersensitivity to barbital and its derivatives, including phenobarbital, or a known previous addiction to sedative-hypnotics. Other contraindications include renal and hepatic impairment and severe pulmonary insufficiency.

Adverse Side Effects

CNS:
The most common manifestations encountered with phenytoin therapy are referable to this system and are usually dose-related. These include nystagmus, ataxia, slurred speech, decreased coordination and mental confusion. Dizziness, insomnia, transient nervousness, motor twitchings, and headaches have also been observed. There have also been rare reports of phenytoin induced dyskinesias, including chorea, dystonia, tremor and asterixis, similar to those induced by phenothiazine and other neuroleptic drugs.
A predominantly sensory peripheral polyneuropathy has been observed in patients receiving long-term phenytoin therapy.

Gastrointestinal:
Nausea, vomiting, and constipation.

Integumentary:
Dermatological manifestations sometimes accompanied by fever have included scarlatiniform or morbilliform rashes. A morbilliform rash (measles-like) is the most common; other types of dermatitis are seen more rarely. Other more serious forms which may be fatal have included bullous, exfoliative or purpuric dermatitis, lupus erythematosus, Stevens-Johnson syndrome and toxic epidermal necrolysis.

Hemopoietic:
Hemopoietic complications, some fatal, have occasionally been reported in association with administration of phenytoin. These have included thrombocytopenia, leukopenia, granulocytopenia, agranulocytosis, and pancytopenia with or without bone marrow suppression. While macrocytosis and megaloblastic anemia have occurred, these conditions usually respond to folic acid therapy. Lymphadenopathy including benign lymph node hyperplasia, pseudolymphoma, lymphoma, and Hodgkins's Disease have been reported.

Connective Tissue:
Coarsening of the facial features, enlargement of the lips, gingival hyperplasia, hypertrichosis and Peyronie's Disease.

Other:
Systemic lupus erythematosus, periarteritis nodosa, toxic hepatitis, liver damage, and immunoglobulin abnormalities may occur.

Overdose

Following acute overdosage of this combination, the patient at steady state may experience evidence of phenytoin toxicity ahead of phenobarbital toxicity because phenytoin plasma levels rise more rapidly than phenobarbital levels. The initial symptoms are nystagmus, ataxia, and dysarthria. Other signs are tremor, hyperflexia, lethargy, slurred speech, nausea, vomiting. The patient may become comatose and hypotensive. Death is due to respiratory and circulatory depression.

In acute overdosage the possibility of other CNS depressants, including alcohol, should be borne in mind.

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