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: Acute hepatitis associated with clopidogrel : a case report and review of the literature .
### Output Text:
Acute hepatitis associated with <span class="chemical">clopidogrel</span> : a case report and review of the literature . 