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: Secondary outcomes were a postdose SCr increase > or = 25 % , a postdose estimated glomerular filtration rate decrease of > or = 25 % , and the mean peak change in SCr .
### Output Text:
Secondary outcomes were a postdose SCr increase > or = 25 % , a postdose estimated glomerular filtration rate decrease of > or = 25 % , and the mean peak change in SCr . 