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.
The eye and optic nerve is an accessible part of the central nervous system, which is why it is being studied closely in neuroprotection. If phenytoin can be shown to work in protecting these nerves during an optic neuritis attack, then it may turn out to be useful in protecting other nerves during and after relapses.
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
If you take phenytoin, you may experience constipation, mild dizziness or mild drowsiness. These are normally transitory and will pass as you adjust to the medication.
Phenytoin may affect your body's ability to digest and use Vitamin D - a GP may advise you to take 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.
- 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.
- Drug Design, Development and Therapy 2018; 12:3485-3489 Full article The retinoprotective role of phenytoin
- Neurological Science 2017 38(6):1137-1141 Summary Phenytoin: neuroprotection or neurotoxicity?
- Expert Review of Neurotherapeutics 2003;3(5):661-671. Summary Therapy of trigeminal neuralgia secondary to multiple sclerosis.