Phenytoin (brand name Dilantin) is a long-standing anti-seizure drug used mainly for tonic-clonic and focal seizures. It works by stabilizing nerve membranes and blocking voltage-gated sodium channels so abnormal electrical activity in the brain is reduced. Doctors often use phenytoin when rapid seizure control is needed or when other options aren't suitable.
Phenytoin comes as pills, chewable tablets, and an IV form for emergency care. Dosing usually starts with a loading dose in the hospital to reach therapeutic levels quickly, then moves to a maintenance dose. Notice that phenytoin has nonlinear (saturable) metabolism: a small dose change can cause a big jump in blood levels. That's why careful dosing and blood level checks matter.
Aim for a therapeutic serum level of about 10-20 mcg/mL for most patients. If levels climb higher, you may see side effects such as dizziness, slurred speech, nystagmus, or ataxia. Long-term use can cause gum overgrowth (gingival hyperplasia), increased hair growth, rashes, and vitamin D deficiency leading to bone issues. Rare but serious reactions like severe skin rash or liver problems need immediate attention.
Phenytoin interacts with many drugs. It induces liver enzymes, which can lower the effectiveness of drugs like warfarin, oral contraceptives, and some newer seizure medications. Also, certain antibiotics, antifungals, and antidepressants can raise phenytoin levels. Always tell every provider and your pharmacist you take phenytoin before starting a new medicine.
Take phenytoin at the same time each day and stick with food instructions from your provider - some forms are best taken with food, others without. Don't stop phenytoin suddenly; abrupt withdrawal can trigger seizures. Keep routine blood work: drug levels, liver tests, and blood counts as recommended. If you are pregnant or planning pregnancy, talk to your neurologist - phenytoin carries a risk of birth defects, but uncontrolled seizures also carry risks.
Brush and floss regularly and see a dentist often to manage gum changes. Avoid alcohol; it can worsen drowsiness and affect drug levels. If you notice a new rash, yellowing skin, unexplained fever, or worsening coordination, call your healthcare team right away.
Expect dose adjustments based on blood levels and side effects, especially in the first weeks. Older adults and people with liver disease may need lower doses. When switching from IV to oral one-to-one dosing may not apply; your clinician will guide the change. Finally, carry a list or card that says you take phenytoin and the dose - it helps in emergencies.
This guide highlights practical, safety-focused points about phenytoin. Ask questions, keep appointments, and work with your care team to balance seizure control and side effects.
Store phenytoin in a cool, dry place out of reach of children. If you change brands or generics, check levels after the switch because absorption can differ. For children and elderly, dosing needs careful follow-up. Keep a seizure diary so your team can judge how the drug works and adjust treatment.
May, 26 2025