Phenytoin: effective but insidious therapy for epilepsy in people with intellectual disability.
Phenytoin can quietly poison the brain in people with ID—monitor closely and be ready to switch.
01Research in Context
What this study did
The author looked at past reports on phenytoin in people with intellectual disability.
He wanted to see how well the drug stops seizures and what hidden problems it can cause.
The paper is a narrative review, not a new trial.
What they found
Phenytoin does control epilepsy, but it can quietly hurt the brain.
Some clients became shaky, confused, or lost skills while levels looked "normal."
The damage can reverse if you catch it early and switch drugs.
How this fits with other research
Alvarez et al. (1998) looked at all seizure drugs the same year. They rank phenytoin and phenobarbital as "last choice" because of thinking side-effects.
Willemsen-Swinkels et al. (1998) praise carbamazepine for the same group, saying it keeps minds clearer.
Pierce et al. (1994) found people living at home were more likely to be on older drugs like phenytoin. The 1998 warning says those homes should now review each prescription.
Why it matters
If your client with ID takes phenytoin, watch for small changes in balance, speech, or self-care. Ask the nurse to check drug levels and request a med review if any signs appear. Swapping to carbamazepine or valproate may keep seizures away and save cognition.
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02At a glance
03Original abstract
Phenytoin (5,5-diphenylhydantoin), which has been in use for 60 years, is still an important antiepileptic drug. Its primary mechanism of action is modulation of the sustained repetitive firing of neurones by direct inhibition and blockage of voltage-gated sodium channels in the neuronal cell membrane, and by delay of cellular reactivation. The plasma protein binding of phenytoin is normally between 90% and 95%. The drug is rapidly distributed from the blood to the tissues and is almost completely metabolized in the liver. The plasma phenytoin concentration normally reaches the steady-state level within 1-2 weeks. The half-life of phenytoin is less than 20 h in low doses, but is prolonged in high doses, newborn infants and elderly people. The half-life is shortened when phenytoin is given concomitantly with an enzyme-inducing drug, such as phenobarbital or carbamazepine. Phenytoin is effective for treating generalized tonic-clonic seizures, partial seizures with or without generalization, and convulsive status epilepticus. Over the years, many new, and even serious, adverse effects of phenytoin have been recognized. Phenytoin encephalopathy, manifesting as cognitive impairment and a cerebellar syndrome, is an important adverse neurological effect, the development of which depends on the saturation kinetics of phenytoin, individual differences in phenytoin metabolism, an inhibitory effect of certain drugs on phenytoin metabolism, or the ability of certain drugs to displace phenytoin from plasma proteins, leading to an increase in the plasma level of unbound phenytoin. Because of its potentially adverse effects, phenytoin is not recommended as the first choice for treating epileptic seizures, except as a co-drug for managing convulsive status epilepticus. In patients with epilepsy who also have intellectual disability, and are susceptible to balance disturbances and cognitive dysfunction, it is wise to replace phenytoin with another drug, such as carbamazepine or oxcarbazepine. The long-term use of phenytoin is not recommended for patients with loss of locomotion, marked cognitive impairment, or symptoms and signs of cerebellar disease. The prevention of phenytoin intoxication, with the subsequent development of phenytoin-induced encephalopathy, depends on careful observation of the patients and frequent monitoring of plasma levels of phenytoin and other concomitantly administered antiepileptic drugs.
Journal of intellectual disability research : JIDR, 1998 · doi:n/a