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 last decade has seen the emergence of tacrolimus as a potent immunosuppressive agent with mechanisms of action virtually identical to those of cyclosporine .
### Output Text:
The last decade has seen the emergence of <span class="chemical">tacrolimus</span> as a potent immunosuppressive agent with mechanisms of action virtually identical to those of <span class="chemical">cyclosporine</span> . 