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: The cardiac depressant actions of phenytoin and hypothermia can be additive .
### Output Text:
The cardiac depressant actions of <span class="chemical">phenytoin</span> and hypothermia can be additive . 