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: We evaluated cardiovascular event data for valdecoxib , a new COX - 2 - specific inhibitor in approximately 8000 patients with osteoarthritis and rheumatoid arthritis treated with this agent in randomized clinical trials .
### Output Text:
We evaluated cardiovascular event data for <span class="chemical">valdecoxib</span> , a new COX - 2 - specific inhibitor in approximately 8000 patients with osteoarthritis and rheumatoid arthritis treated with this agent in randomized clinical trials . 