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: Proteinuria correlated most strongly with sirolimus therapy when compared to other demographic and clinical variables .
### Output Text:
Proteinuria correlated most strongly with <span class="chemical">sirolimus</span> therapy when compared to other demographic and clinical variables . 