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: The pattern of non - specific acute tubular necrosis found in the 2 biopsied patients , indistinguishable from that of ischemic origin , raised the possibility of a vascular - mediated damage .
### Output Text:
The pattern of non - specific acute tubular necrosis found in the 2 biopsied patients , indistinguishable from that of ischemic origin , raised the possibility of a vascular - mediated damage . 