Phenytoin safety tips: what to know and what to do
If you take phenytoin (Dilantin) or care for someone who does, simple habits cut risk. This guide gives clear, practical tips you can use today — how to spot problems, what to tell your doctor, and everyday actions that keep treatment working.
Monitoring & warning signs
Ask your provider about regular blood tests. Phenytoin has a usual total blood range of about 10–20 mcg/mL; some people need a free level measured (especially if low albumin or kidney disease). Also get liver tests and a CBC now and then — rare but serious blood or liver problems can occur.
Watch for these signs of too much drug: nystagmus (eyes jumping), poor coordination, slurred speech, confusion, severe sleepiness. If any of these start suddenly, call your clinician or go to the ER. If you develop a rash, fever, swollen glands, or trouble breathing, stop the drug and seek urgent care — some rashes can be life-threatening.
Drug interactions and special situations
Phenytoin changes how many drugs work and many drugs change phenytoin levels. It induces liver enzymes (like CYP3A4), so it can lower effectiveness of birth control pills and some other meds. Drugs that can raise phenytoin levels include certain antifungals and antibiotics, while smoking, chronic alcohol, and some other meds can lower levels.
Valproate and phenytoin interact in complex ways — your provider will check levels when both are used. Warfarin dose may also need adjustment. Always tell every clinician, dentist, and pharmacist that you take phenytoin before they start new meds or vaccines.
Practical daily tips
Take phenytoin the same way every day — with food if it bothers your stomach — and at the same time(s) to keep levels steady. Never skip doses or double up without checking with your provider. If you miss a dose, follow the instructions on your prescription or ask your pharmacist.
Do not stop phenytoin suddenly; that can trigger seizures. If you want to stop, your doctor should taper the dose. Carry a list of your medicines or wear a medical ID that notes you take phenytoin.
Good oral care helps — long-term phenytoin can cause gum overgrowth. Brush, floss, and see a dentist regularly. Women who could get pregnant should talk about folic acid and birth control options; phenytoin can raise risk of birth defects.
If you get IV phenytoin in hospital, it must be given slowly by trained staff because fast IV speed can cause low blood pressure or heart problems. Store pills at room temperature, away from moisture and heat, and refill before you run out.
Keep communication open: bring up side effects, missed doses, or new medicines at each visit. Small checks — a blood test, a conversation about headaches or sleepiness, and clear instructions — make phenytoin much safer and more effective.