Other name: Epanutin
Phenytoin is an anti-convulsant drug that works on the brain and spinal cord. Its main use is in epilepsy. In MS it can be used to treat trigeminal neuralgia or other painful sensations (dysaesthesia) if other approaches have not worked.
Phenytoin has been studied as a potential neuroprotective drug. Results of a phase II study of 82 people with optic neuritis were announced at a conference in April 2015 and published in the Lancet Neurology in January 2016. Researchers found that people who had been treated with phenytoin over three months showed 30% less damage to nerve cells in the retina than people taking a placebo.
How phenytoin is given
Phenytoin is given orally as tablets.
Phenytoin can remain in the body for some time after treatment has stopped so it is important to taper off treatment gradually rather than stopping abruptly.
Side effects and contraindications
Constipation, mild dizziness, mild drowsiness. These are normally transitory and will pass as an individual adjusts to the medication.
Phenytoin may affect an individual's ability to metabolise Vitamin D - a GP may advise supplements. Phenytoin may reduce the effectiveness of some oral contraceptives and can interact with fluoxetine (Prozac), paroxetine (Seroxat) and St John's wort.
People should not take phenytoin if they have liver dysfunction. It should also be avoided during pregnancy or whilst still breastfeeding.
Last updated: January 2016
Last reviewed: April 2015
This page will be reviewed within three years
- Lancet Neurology 2016 Jan 25 [Epub ahead of print]. Summary Phenytoin for neuroprotection in patients with acute optic neuritis: a randomised, placebo-controlled, phase II trial.
- Expert Review of Neurotherapeutics 2003;3(5):661-671. Summary Therapy of trigeminal neuralgia secondary to multiple sclerosis.