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: The results of this pilot study suggest that fusidic acid may be of benefit in selected chronic active Crohn ' s disease patients in whom conventional treatment is ineffective .
### Output Text:
The results of this pilot study suggest that <span class="chemical">fusidic acid</span> may be of benefit in selected chronic active Crohn ' s disease patients in whom conventional treatment is ineffective . 