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: In the study presented here , we investigated the use of dexamethasone in combination with mesna for the prevention of IFS - induced HC .
### Output Text:
In the study presented here , we investigated the use of <span class="chemical">dexamethasone</span> in combination with <span class="chemical">mesna</span> for the prevention of <span class="chemical">IFS</span> - induced HC . 