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: Because there seems to exist a scientific rationale for the use of fusidic acid at the cytokine level in inflammatory bowel disease , we suggest that the role of this treatment should be further investigated .
### Output Text:
Because there seems to exist a scientific rationale for the use of <span class="chemical">fusidic acid</span> at the cytokine level in inflammatory bowel disease , we suggest that the role of this treatment should be further investigated . 