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: METHODS : We performed a case control study of heart failure patients treated with spironolactone in our clinical practice .
### Output Text:
METHODS : We performed a case control study of heart failure patients treated with <span class="chemical">spironolactone</span> in our clinical practice . 