Phenytoin, sold under the brand name Dilantin among others, is an anti-seizure medication. It is a compound approved by the FDA in 1953 for the prevention of seizures. It acts by blocking undesired brain activity by reducing the electric conductivity between the neurons, blocking voltage sensitive sodium channels. By blocking the cardiac solium channels, phenytoin acts as an antiarrhythmic agent.
Phenytoin can be used alone or in combination with other anticonvulsive drugs such as phenobarbital. It can also be used to prevent seizures that happen during surgery but it is not used in absence seizures (petit mal).
The clinical management of phenytoin is more complicated than in other anticonvulsant drugs because it has a non lineal pharmacokinetic; it binds in great measure to the plasma proteins and has a high interindividual variability in its bioavailability.
Mechanism of action: anticonvulsant drugs raise the threshold of the seizures and/ or reduce their intensity. Phenytoin acts by limiting the diffusion of the discharges and their spread in contrast to phenobarbital and carbamazepine that raise the threshold of the seizures. For this reason, phenytoin is less effective preventing the seizures produced by drugs or electro-induced seizures. The effects of phenytoin depend on its action on the sodium channels of the neuronal cell membrane. Its anticonvulsive effects have less sedating effects than phenobarbital. In large doses, phenytoin causes excitability and induces seizures. Because of its effects on the sodium channels, phenytoin is slightly antiarrhythmic, acting on the Purkinje fibers.