Phenytoin is used to control certain type of seizures, and to treat and prevent seizures that may begin during or after surgery to the brain or nervous system. Phenytoin is in a class of medications called anticonvulsants. It works by decreasing abnormal electrical activity in the brain.
Variations in the CYP2C9 gene can affect the rate at which Phenytoin is removed from the body. People with reduced ability to metabolize Phenytoin would need to have their dose reduced in order to avoid side effects, while people who metabolize the drug more rapidly, might need to have their dose increased for the drug to be effective.