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: In each patient , the close temporal association between the commencement of sirolimus therapy and proteinuria implicated sirolimus as the most likely etiology of the proteinuria .
### Output Text:
In each patient , the close temporal association between the commencement of <span class="chemical">sirolimus</span> therapy and proteinuria implicated <span class="chemical">sirolimus</span> as the most likely etiology of the proteinuria . 