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 aim of this work is to call attention to the risk of tacrolimus use in patients with SSc .
### Output Text:
The aim of this work is to call attention to the risk of <span class="chemical">tacrolimus</span> use in patients with SSc . 