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Phenytoin is an anticonvulsant and cardiac depressant used in the treatment of all forms of epilepsy except petit mal and as an antiarrhythmic, where it is particularly useful against arrhythmias caused by cardiac glycosides.
The mode of action of phenytoin is to block repetitive firing of neurons by action on voltage sensitive Na channels.
It is has little effect on myoclonus.
The summary of product characteristics should be consulted before prescribing this drug.