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: In the two patients , skin and ELISA tests with paramethasone were negative , as was the prick test with each of its excipients .
### Output Text:
In the two patients , skin and ELISA tests with <span class="chemical">paramethasone</span> were negative , as was the prick test with each of its excipients . 