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: Development of proteinuria after switch to sirolimus - based immunosuppression in long - term cardiac transplant patients .
### Output Text:
Development of proteinuria after switch to <span class="chemical">sirolimus</span> - based immunosuppression in long - term cardiac transplant patients . 