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: 7 days later , the fever disappeared and the patient ' s serum CPK levels were normalized ( 175 IU / L ) .
### Output Text:
7 days later , the fever disappeared and the patient ' s serum CPK levels were normalized ( 175 IU / L ) . 