Known brand names include Dilantin and Phenytek.
An antiepileptic (anticonvulsant) taken by mouth as extended-release capsules. It treats tonic-clonic and temporal lobe seizures and prevents or treats seizures during or after neurosurgery. Blood levels guide dosing because small dose changes can cause big level changes.
Phenytoin is thought to block sodium channels on nerve cells, though the exact way it works has not been proven. That cuts down the rapid, repeated firing of nerve cells and calms the abnormal electrical activity in the brain that drives seizures. The liver breaks it down, mainly with an enzyme called CYP2C9, and the inactive products leave the body through bile and urine.
With the capsules, blood levels peak 4 to 12 hours after a dose, and it takes at least 7 to 10 days of regular use to reach a steady level. The liver can only break down so much at once, so near the top of the usual range a small dose increase can push the blood level up sharply and cause toxic effects. Levels vary widely between people on the same dose and run higher with liver disease, certain inherited enzyme differences, or interacting drugs. It also speeds up the liver's breakdown of many other drugs.
Phenytoin is a seizure medicine taken as long-acting capsules. It treats tonic-clonic seizures, which cause stiffening and jerking of the whole body, and seizures that start in the temporal lobe of the brain. It also prevents and treats seizures during or after brain surgery. It is meant to control seizures, and it does not cure the condition behind them.
Both adults and children take it by mouth, and the capsules are swallowed whole. It is taken every day, even when the person feels well, and stopping it suddenly can bring on nonstop seizures. Different phenytoin products are absorbed differently, so one cannot simply be swapped for another.
Jerky eye movements, unsteadiness, slurred speech, dizziness, drowsiness, and gum overgrowth are what people notice most. Nausea, constipation, coarser facial features, and higher blood sugar can also happen. The label treats severe skin reactions as dangerous, usually in the first weeks, along with whole-body allergic reactions, liver injury, blood disorders, a slow heartbeat, bone loss, suicidal thoughts, and nonstop seizures after stopping suddenly.
A clinician may order these while someone is taking it.