In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: We conclude that phenytoin overdosage does not necessarily result in cerebellar atrophy and it is unlikely that phenytoin medication was the only cause of cerebellar atrophy in the remaining patients .
### Output Text:
We conclude that <span class="chemical">phenytoin</span> overdosage does not necessarily result in cerebellar atrophy and it is unlikely that <span class="chemical">phenytoin</span> medication was the only cause of cerebellar atrophy in the remaining patients . 