Dilantin (phenytoin) is an anti-epileptic drug, commonly called an anticonvulsant, which works works by slowing impulses in the brain that are likely to cause seizures.
Phenytoin may not treat all types of seizures, or may not treat them well, and your doctor will determine if it is the best medicine for you.
Phenytoin was first created way back in 1908. Yes, 1908. Since the chemist who created it could not figure out what to do with his creation, he sold it and in 1938, the company who bought the drug figured out that it could control seizures. No word on what they did with it in the intervening three decades.
In 1953, the FDA approved the use of Phenytoin for seizure control, and in 2008, it was put on the FDA's Potential Signals of Serious Risks List - meaning that over the last hundred years or so, they might have missed something, but they are still looking.
It also seems that just about anything can interfere with Dilantin, including antibiotics, antidepressants, aspirin, blood thinners, other seizure medicines and even antacids.
This description is adapted from information sources found online, and is in no way meant to replace or substitute for professional medical advice. If you are in pain, or considering taking this or any other medicine, contact your medical professional for assistance rather than using the internet as your sole source of information.
My Personal Experience
One thing I never saw or heard listed as an interaction - in something like twenty years of taking Dilantin! - was a decongestant. Seriously. Since I had a problem with sinuses, I would happily munch away on Sudafed (or something similar, in the days before pseudoephedrine became known for meth), and wouldn't you know it, my blood tests would come back with almost no Dilantin? Turns out it was because of the decongestants. You would think someone may have thought of that in all those years.
Regardless, shortly after being prescribed Dilantin, I took as much as 500mg a day for more than twenty years - but since Dilantin (phenytoin) isn't widely regarded, it was determined that it's time to move on before something else manifests itself, and so I was weaned off and onto something new - in this case, Zonegran seems like it will be the winner.
As I was decreasing this dose, I did go through a period where I had a serious headache for a while, but it was nothing that a good amount of Ibuprofen couldn't help with, and once I was switched over to Zonegran - and more importantly, not taking both at the same time - the headaches seemed to stop being an issue on a regular basis.