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: Mesna significantly reduces IFO ' s genotoxicity , while when administered in high concentrations it acts in an inhibitory fashion on the cytostatic action of the drug .
### Output Text:
<span class="chemical">Mesna</span> significantly reduces <span class="chemical">IFO</span> ' s genotoxicity , while when administered in high concentrations it acts in an inhibitory fashion on the cytostatic action of the drug . 