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: Safety of celecoxib in patients with adverse skin reactions to acetaminophen ( paracetamol ) and nimesulide associated or not with common non - steroidal anti - inflammatory drugs .
### Output Text:
Safety of <span class="chemical">celecoxib</span> in patients with adverse skin reactions to <span class="chemical">acetaminophen</span> ( <span class="chemical">paracetamol</span> ) and <span class="chemical">nimesulide</span> associated or not with common non - steroidal anti - inflammatory drugs . 