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: Gastrointestinal tolerability of etoricoxib in rheumatoid arthritis patients : results of the etoricoxib vs diclofenac sodium gastrointestinal tolerability and effectiveness trial ( EDGE - II ) .
### Output Text:
Gastrointestinal tolerability of <span class="chemical">etoricoxib</span> in rheumatoid arthritis patients : results of the <span class="chemical">etoricoxib</span> vs <span class="chemical">diclofenac sodium</span> gastrointestinal tolerability and effectiveness trial ( EDGE - II ) . 