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 direct nephrotoxic effects of a single dose of 15 mg of suprofen were compared in the recirculating isolated rat kidney perfused with cell - free buffer with or without the addition of 5 mg / dL of uric acid .
### Output Text:
The direct nephrotoxic effects of a single dose of 15 mg of <span class="chemical">suprofen</span> were compared in the recirculating isolated rat kidney perfused with cell - free buffer with or without the addition of 5 mg / dL of <span class="chemical">uric acid</span> . 