Hi there,
Dilantin (What I call Phenytoin in the UK!) has quite a few side effects as it is quite an old med but there is a new formulation which has just started circulation in the last few months so some of these may now be in correct. I have found a list of SE's for you:
More common
Bleeding, tender, or enlarged gums (rare with ethotoin); burning, tingling, pain, or itching, especially in the groin—following fosphenytoin injection; clumsiness or unsteadiness; confusion; continuous, uncontrolled back-and-forth and/or rolling eye movements—may be sign of overdose; swollen glands in neck or underarms; fever; muscle pain; skin rash or itching; slurred speech or stuttering—may be sign of overdose; sore throat; trembling—may be sign of overdose; unusual excitement, nervousness, or irritability
Rare
Bone malformations; burning pain at place of injection; chest discomfort; chills and fever; dark urine; dizziness; frequent breaking of bones; headache; joint pain; learning difficulties—in children taking high doses for a long time; light gray-colored stools; loss of appetite; nausea or vomiting; pain of penis on erection; restlessness or agitation; slowed growth; stomach pain (severe); troubled or quick, shallow breathing; uncontrolled jerking or twisting movements of hands, arms, or legs; uncontrolled movements of lips, tongue, or cheeks; unusual bleeding (such as nosebleeds) or bruising; unusual tiredness or weakness; weight loss (unusual); yellow eyes or skin
Rare (with long-term use of phenytoin)
Numbness, tingling, or pain in hands or feet
Symptoms of overdose
Blurred or double vision; clumsiness or unsteadiness (severe); confusion (severe); dizziness or drowsiness (severe); seizures; staggering walk; stuttering or slurred speech
Hope this helps
Darren