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: Reports about cases of hepatotoxicity due to clopidogrel are increasing in the last few years , after the increased use of this drug .
### Output Text:
Reports about cases of hepatotoxicity due to <span class="chemical">clopidogrel</span> are increasing in the last few years , after the increased use of this drug . 