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: Preliminary results at 400 and 500 mg / m2 suggest that a reduction in nephrotoxicity may have been achieved with only 1 instance of renal toxicity in 10 patients .
### Output Text:
Preliminary results at 400 and 500 mg / m2 suggest that a reduction in nephrotoxicity may have been achieved with only 1 instance of renal toxicity in 10 patients . 