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: An objective causality assessment revealed that the adverse drug event was probably related to the use of ticlopidine .
### Output Text:
An objective causality assessment revealed that the adverse drug event was probably related to the use of <span class="chemical">ticlopidine</span> . 