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: These observations suggest that statins may initiate an immune - mediated myopathy that persists after withdrawal of the drug and responds to immunosuppressive therapy .
### Output Text:
These observations suggest that <span class="chemical">statins</span> may initiate an immune - mediated myopathy that persists after withdrawal of the drug and responds to immunosuppressive therapy . 