Phenytoin Sodium
Introduction
Phenytoin is an anticonvulsant medication used primarily in the treatment of:
- Tonic-clonic seizures; focal seizures. A period of 5-10 days may be required to achieve anticonvulsant effects.
- Treatment of seizures during or following neurosurgery or severe head injury;
- Status epilepticus;
- Trigeminal neuralgia if carbamazepine inappropriate;
- Abnormal heart rhythm such as ventricular tachycardia and atrial tachycardia.
Pronunciation
Phenytoin sodium 100mg
Phenytoin sodium 30mg
| Generic Name 藥名 | HA Code 藥物代碼 | Classification藥物分類 |
|---|---|---|
| Phenytoin Sodium Cap 30mg | PHEN31 | P1S1S3 |
| Phenytoin Sodium Extended | ||
| Release Cap 100mg | PHEN86 | P1S1S3 |
Mechanism of Action
Anticonvulsant medication. It is a sodium channel blocker. It binds to sodium channels and suppresses repetitive neuronal firing.
Dosage
Doses may be expressed in terms of phenytoin or phenytoin sodium; phenytoin 92 mg is equivalent to about 100 mg phenytoin sodium.
As phenytoin has a narrow therapeutic index, need to monitor plasma-phenytoin concentration.
Anticonvulsant effect: 10-20 micrograms/mL (40 to 80 micromoles/litre)
Antiarrhythmic effect: 10-20 micrograms/mL (40 to 80 micromoles/litre)
By mouth, initially 3-4 mg/kg daily or 150 – 300 mg daily (as a single dose or in 2 divided doses) increased gradually as necessary to 600 mg daily. The suggested minimum interval between increments has ranged from about 7 to 10 days. A usual maintenance dose is 200 – 500 mg daily.
For doses in children.
To lessen gastric irritation, phenytoin should be taken with or after food.
As with other antiepileptics, withdrawal of phenytoin therapy or transition to or from another type of antiepileptic therapy should be made gradually to avoid precipitating an increase in seizure frequency.
Side Effects
Common side effects include:
- CNS-related effects such as headaches, dizziness, tremor, transient nervousness and insomnia;
- Gastrointestinal disturbances, such as nausea , vomiting, stomach pain, loss of appetite and constipation.
- Enlargement of the gums and tenderness (maintain good oral hygiene)
- Acne, increased hair growth and coarsening of facial appearance, may be particularly undesirable in adolescents and women.
Potentially serious side effects include:
- Self-harm
- Liver problems
- Bone marrow suppression
- Low blood pressure: severe low blood pressure and abnormal heartbeat rhythms can be seen with rapid infusion of IV phenytoin
- Toxic epidermal necrolysis
Phenytoin toxicity may be manifested as:
- Syndrome of cerebellar, vestibular, and ocular effects, notably nystagmus, double vision, slurred speech, and ataxia
- Mental confusion
- Dyskinesias
- hyperglycaemia
Neurological: Phenytoin may accumulate in the cerebral cortex over long periods of time which can cause atrophy of the cerebellum. The degree of atrophy is related to the duration of phenytoin treatment and is not related to dosage of the medication.
Blood: Phenytoin blocks the gut absorption of folate in food, thereby causing folate deficiency, and thus megaloblastic anaemia. Other side effects may include agranulocytosis, aplastic anaemia, decreased white blood cell count, and a low platelet count.
Skin: Hypertrichosis, purple glove syndrome, rash, exfoliative dermatitis, itching, excessive hairiness, and coarsening of facial features cab be seen in those taking phenytoin. Also, phenytoin has been linked to the life-threatening skin reactions Stevens-Johnson syndrome and toxic epidermal necrolysis. Test for HLA-B*1502 allele in individuals of Han Chinese or Thai origin (avoid unless no alternative – risk of Stevens-Johnson syndrome in presence of HLA-B*1502 allele).
Immune system: phenytoin has been known to cause drug-induced lupus.
Psychological: Phenytoin may increase risk of suicidal thoughts or behaviour.
Bone: phenytoin has been associated with decreased bone density (osteoporosis) and increased bone fractures.
