What Causes A Catastrophic Epilepsy?

QUESTION: Would the following result in a seizure catastrophe? A 93 year old senior citizen male has been diagnosed with seizures since the year of 2012. The type of seizure/cause remains unknown but since has been instructed to take (2)100mg phenoytoin capsules in both the morning and evening, equaling 400mg total per day. This regiment has resulted in (0) zero seizures for 5 years. As of Today (3/15/17) the 93 year old s dosage has been changed to a reduction of 300mg on an an every-other-day routine. Resulting in: one day he takes his full 400mg dosage , the next he only takes 300mg. This new regiment however, is only to last for two weeks in order for the Dilantin in his blood level to be checked . QUESTION: Would this make this 93 year patient vulnerable to a Seizure; reducing 1, 100mg cap every other day for two weeks?