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: What is less well known is a phenomenon whereby statins may induce a myopathy , which persists or may progress after stopping the drug .
### Output Text:
What is less well known is a phenomenon whereby <span class="chemical">statins</span> may induce a myopathy , which persists or may progress after stopping the drug . 