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: CONCLUSIONS : Nephropathy induced by contrast medium may be less likely to develop in high - risk patients when iodixanol is used rather than a low - osmolar , nonionic contrast medium .
### Output Text:
CONCLUSIONS : Nephropathy induced by contrast medium may be less likely to develop in high - risk patients when <span class="chemical">iodixanol</span> is used rather than a low - osmolar , nonionic contrast medium . 