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 second episode was more severe than the first ; and although both were treated with intensive corticosteroid therapy , renal function remained impaired .
### Output Text:
The second episode was more severe than the first ; and although both were treated with intensive corticosteroid therapy , renal function remained impaired . 