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: Although statins are generally well - tolerated drugs , recent cases of drug - induced liver injury associated with their use have been reported .
### Output Text:
Although <span class="chemical">statins</span> are generally well - tolerated drugs , recent cases of drug - induced liver injury associated with their use have been reported . 