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: This case suggests that the psychotic symptoms that occur following phenytoin treatment in some epileptic patients may be the direct result of medication , unrelated to seizures .
### Output Text:
This case suggests that the psychotic symptoms that occur following <span class="chemical">phenytoin</span> treatment in some epileptic patients may be the direct result of medication , unrelated to seizures . 