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: DISCUSSION : Cholestatic hepatitis is a rare complication of the antiplatelet agent ticlopidine ; several cases have been reported but few in the English literature .
### Output Text:
DISCUSSION : Cholestatic hepatitis is a rare complication of the antiplatelet agent <span class="chemical">ticlopidine</span> ; several cases have been reported but few in the English literature . 