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: A total of 75 / 829 ( 9 . 4 % ) patients experienced reactions to nimesulide or paracetamol .
### Output Text:
A total of 75 / 829 ( 9 . 4 % ) patients experienced reactions to <span class="chemical">nimesulide</span> or <span class="chemical">paracetamol</span> . 