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: CONCLUSION : Dexamethasone in combination with mesna was efficient in blocking IFS - induced HC .
### Output Text:
CONCLUSION : <span class="chemical">Dexamethasone</span> in combination with <span class="chemical">mesna</span> was efficient in blocking <span class="chemical">IFS</span> - induced HC . 