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: In conclusion , we believe that physicians should carefully consider the risk of drug - induced hepatic injury when clopidogrel is prescribed .
### Output Text:
In conclusion , we believe that physicians should carefully consider the risk of drug - induced hepatic injury when <span class="chemical">clopidogrel</span> is prescribed . 