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.
Narrow therapeutic index. The label sets a target total serum level of 10 to 20 mcg/mL and warns that levels sustained above that range cause toxicity.
None on the oral Dilantin extended capsule label. Withdrawal seizures, severe skin reactions, and hepatotoxicity are labeled warnings.
No antidote. Early overdose signs are nystagmus, ataxia, and slurred speech, progressing to lethargy, coma, hypotension, bradycardia, and cardiac arrest. Support breathing and circulation; hemodialysis can be considered. Consider other CNS depressants such as alcohol.
Sources: [1]
Doses come from the FDA label. Study tool, not for clinical decisions.
No set dose change, but the unbound fraction rises in renal disease. Base monitoring on unbound (free) phenytoin levels. Avoid the oral loading regimen.
Thought to block voltage-dependent sodium channels, which limits sustained high-frequency neuronal firing. It is highly protein bound and metabolized by CYP2C9 and CYP2C19. Metabolism saturates at higher levels, so a small dose increase can raise levels sharply. It is also a potent inducer of liver drug-metabolizing enzymes. Half-life averages 22 hours.