The folic acid in Multivitamin [water & fat soluble] + 5% Dextrose may increase the metabolism of phenytoin, an antiepileptic medicine. That means the body may break phenytoin down faster when the two are taken together.
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.