PHENYTOIN SODIUM TABLETS係咩藥and有咩副作用

Phenytoin sodium is a commonly used antiepileptic. It was approved by the Food and Drug Administration in 1953 for use in seizures. Phenytoin acts to damp the unwanted, runaway brain activity seen in seizure by reducing electrical conductance among brain cells by stabilizing the inactive state of voltage gated sodium channels. Aside from seizures, it is an option in the treatment of trigeminal neuralgia as well as certain cardiac arrhythmias.


Side-effects
At therapeutic doses, phenytoin produces horizontal gaze nystagmus, which is harmless but occasionally tested for by law enforcement as a marker for alcohol intoxication (which can also produce nystagmus). At toxic doses, patients experience sedation, cerebellar ataxia, and ophthalmoparesis, as well as paradoxical seizures. Idiosyncratic side effects of phenytoin, as with other anticonvulsants, include rash and severe allergic reactions.

It has been suggested that phenytoin causes a reduction in folic acid levels, predisposing patients to megaloblastic anemia. Folic acid is presented as polyglutamate in foods, it is then converted into monoglutamates by intestinal conjugase. Now phenytoin acts by inhibiting this enzyme therefore causing folate deficiency. [2]

There is some evidence that phenytoin is teratogenic, causing what Smith and Jones in their Recognizable Patterns of Human Malformation called the fetal hydantoin syndrome.[citation needed] There is some evidence against this.[citation needed] One blinded trial asked physicians to separate photographs of children into two piles based on whether they showed the so-called characteristic features of this syndrome; it found that physicians were no better at diagnosing the syndrome than would be expected by random chance, calling the very existence of the syndrome into question.[citation needed] Data now being collected by the Epilepsy and Antiepileptic Drug Pregnancy Registry may one day answer this question definitively. The CDC lists fetal hydantoin syndrome as a rule-out for differential diagnosis of Fetal alcohol syndrome due to overlapping facial and intellectual symptoms.[3]

Phenytoin may accumulate in the cerebral cortex over long periods of time, as well as causing atrophy of the cerebellum when administered at chronically high levels. Despite this, the drug has a long history of safe use, making it one of the more popular anti-convulsants prescribed by doctors, and a common "first line of defense" in seizure cases. Phenytoin also commonly causes gingival hyperplasia due to folate deficiency.

Recently phenytoin is suggested to be a human carcinogen. [4]

Due to patent expiration, phenytoin is available in generic form and several branded forms at relatively low cost, making it one of the more affordable seizure control medications. It is available in extended release capsules and injectable forms, though the injectable formulation is rapidly losing ground to fosphenytoin (an important side note is that fosphenytoin has to be dephosphoralated before it can metabolized for use which can take an extra 15 minutes). Some generic formulations of phenytoin have been felt to be less reliable with respect to time-release than their branded counterparts. In some cases, this can be related to complications which arise between the alternative protein bond release mechanisms used in the generic versions, and those individuals with high metabolic rates.