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: Intravenous phenytoin was administered during the later part of the surgery for seizure prophylaxis .
### Output Text:
Intravenous <span class="chemical">phenytoin</span> was administered during the later part of the surgery for seizure prophylaxis . 