Cenobamate and phenytoin are both used for seizures. If you take them together, your doctor may need to lower your phenytoin dose slowly, by up to half (50%). Don't change or stop phenytoin on your own. Any reduction should be planned and supervised by your doctor.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.