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 addition to this , when high concentrations of Mesna were administered alone significant reductions of the PRI were noted , than with IFO acting at the same concentration on the lymphocytes .
### Output Text:
In addition to this , when high concentrations of <span class="chemical">Mesna</span> were administered alone significant reductions of the PRI were noted , than with <span class="chemical">IFO</span> acting at the same concentration on the lymphocytes . 