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: Lack of teratogenicity was found in piroxicam and DFU - exposed groups .
### Output Text:
Lack of teratogenicity was found in <span class="chemical">piroxicam</span> and <span class="chemical">DFU</span> - exposed groups . 