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: RESULTS : The creatinine concentration increased significantly less in patients who received iodixanol .
### Output Text:
RESULTS : The <span class="chemical">creatinine</span> concentration increased significantly less in patients who received <span class="chemical">iodixanol</span> . 