Get emergency medical help if you have signs of an allergic reaction to phenytoin (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning in your eyes, skin pain, red or purple skin rash that spreads and causes blistering and peeling).
Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.
Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), more depressed, or have thoughts about suicide or hurting yourself.
Call your doctor at once if you have:
slow or uneven heartbeats, chest pain, fluttering in your chest, and dizziness (like you might pass out);
any skin rash, no matter how mild;
fever, chills, sore throat, swollen glands;
red or swollen gums, mouth sores;
easy bruising, unusual bleeding, purple or red spots under your skin; or
liver problems - loss of appetite, upper stomach pain, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).
Common phenytoin side effects may include:
drowsiness, confusion;
slurred speech;
abnormal eye movement; or
problems with balance, coordination, or muscle movement.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Phenytoin side effects (more detail)
