Ethotoin, phenobarbital, ethosuximide, trimethadione or if you have phenytoin jotta any other allergies. Oxcarbazepine may increase the serum concentration of Phenytoin. Risk X: Avoid combination Rifamycin Derivatives: May increase the metabolism of Phenytoin. If you get an upset stomach and want to take an antacid or medicine for diarrhea, make sure there is an interval of to hours before or after you took your phenytoin. Also tell them if you smoke, drink alcohol, or use illegal drugs. As much as 25 times the therapeutic dose has been taken to result in serum concentration over 100 mcg mL with complete recovery. The great majority of mothers on antiepileptic medication deliver normal infants.