If you're taking Dilantin (phenytoin) or caring for someone who is, you want straight answers: what side effects are normal, which need urgent care, and how to reduce risks. Phenytoin works well for many types of seizures, but it has some side effects that come up often and a few that are serious. This short guide tells you what to expect and what to do.
Many people notice mild effects that often improve after a few weeks or when the dose is adjusted. Expect possible drowsiness, dizziness, or unsteady walking (ataxia). Nystagmus — rapid eye movements — can show up at higher doses. Routine problems also include nausea, upset stomach, and trouble concentrating.
Two side effects you’ll hear about a lot are gum overgrowth (gingival hyperplasia) and acne or increased hair growth. Good oral hygiene and regular dental check-ups help a lot. Long-term use can sometimes affect bone density, so talk to your doctor about calcium and vitamin D if you’ll be on phenytoin for years.
Some reactions need immediate medical attention. Watch for a new or spreading skin rash, especially if it comes with fever — that could be a severe allergic reaction like Stevens-Johnson syndrome. Also seek help for yellowing of the skin or eyes (jaundice), dark urine, or persistent stomach pain — signs of liver trouble.
If you have unexplained bruising, bleeding, sore throat, or very high fevers, those could mean blood problems (low white cells or platelets) and need quick evaluation. Extreme dizziness, fainting, slurred speech, or confusion may signal toxic levels and should prompt urgent care.
Phenytoin has a narrow therapeutic range. Most labs aim for a total phenytoin level of about 10–20 µg/mL. Your doctor may check blood levels, liver tests, and sometimes blood counts to make sure the dose is safe for you.
Drug interactions are common because phenytoin strongly affects liver enzymes. That can lower the effect of some birth control pills, warfarin, and many other drugs — or make other drugs change phenytoin levels. Tell your prescriber and pharmacist about every medication, supplement, and herb you use.
Practical tips: always take Dilantin at the same time each day and don’t stop it suddenly — that can trigger seizures. Avoid heavy drinking and discuss pregnancy plans with your doctor; phenytoin can have risks in pregnancy but stopping suddenly is also dangerous. Brush and floss regularly to reduce gum issues, and tell your dentist you’re on phenytoin.
If you notice worrying symptoms, call your healthcare provider or get urgent care. Keep a list of your medicines, know when your last blood level was checked, and ask for clear follow-up when your dose changes. With careful monitoring, many people use Dilantin effectively and safely.
May, 26 2025