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phenytoin

Generic name: Phenytoin

Available as: Epanutin: chewable infatabs 50mg, oral suspension 30mg/5ml.
Phenytoin: tablets 100mg.
​Phenytoin Sodium Flynn: hard capsules 25mg, 50mg, 100mg, 300mg.

Adults

Average total daily dose: 200mg – 500mg daily divided into 1 or 2 doses

Doses per day: 1 – 2

Treatment: Effective for focal and tonic clonic seizures. Ineffective against absences. Blood testing is essential to guide the doses.

Most common possible side effects include the following. Report severe reactions, such as a skin rash, to your doctor.
Skin rash. Nausea, vomiting, constipation, drowsiness, insomnia, nervousness, tremor, pins and needles, dizziness, headache, anorexia, gum problems, acne, excess hair growth, and coarsening of facial features.

Children

Average total daily dose: 1 month – 12 years: 7.5mg/kg twice daily or 300mg daily. From 12 years: 150 – 200mg twice daily to max 300mg twice daily.

Doses per day: 2

Treatment: Effective for all seizure types except absence seizures. Blood testing is essential as the relationship between dose and blood level is complex.

Most common possible side effects include the following. Report severe reactions, such as a skin rash, to your doctor.
Skin rash if allergic to phenytoin. Nausea, vomiting, constipation, insomnia (not able to sleep), tremor, pins and needles, dizziness and headache. Can cause coarse facial features, acne, hirsutism (excess hair) and overgrowth of gums if used over a long time.

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Please note:

  • This information is a guide only, and lists the usual daily doses of anti-epileptic drugs (AEDs). The dose taken may be different to those listed above.

  • Treatment of neonatal seizures (from birth to 28 days of age) is not covered.

  • Most doses are listed as ‘mg/kg’: this means milligrams of AED per kg of the child’s weight.

  • Children starting AED treatment at the age of 12 may start on adult doses. Some AEDs are only used for children aged 12 and over (including eslicarbazepine acetate, lacosamide, perampanel, pregabalin, retigabine and tiagabine).

  • Some AED doses are listed as ‘twice daily’ (for example ‘5mg/kg twice daily’). This means that the dose listed is taken each time (and so the total daily dose will be double that listed).

  • Some AED doses are listed as ‘divided into 2 (or 3) doses’ (for example ‘25 - 30mg/kg daily divided into 2 doses’). This means that the total amount listed is divided into two to give the dose taken each time.

  • ‘Effective’ means the seizures it works for. ‘Monotherapy’ means the AED is taken on its own. ‘Add-on therapy’ means the AED is taken alongside other AEDs. ‘Tolerance’ means that a drug becomes less effective the longer you take it.

  • Information for this page comes from sources including the British National Formulary (BNF), the British National Formulary for children (BNFC) and the electronic medicines Compendium (eMC). The side effects listed here are some of the most common possible side effects and may be worded differently in the patient information leaflet for the AED. Doctors may refer to the BNF/BNFC for starting doses and how to increase doses. For more details, and a complete list of side effects, visit medicines.org.uk/emc(opens new window).

  • Every effort is made to ensure that all information is correct at time of publishing but information may change after publication. This information is not a substitute for advice from your doctor. Epilepsy Society is not responsible for any actions taken as a result of using this information.