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: Fourteen days after hospitalization , creatine kinase level had returned to 230 IU / L and the patient was discharged .
### Output Text:
Fourteen days after hospitalization , <span class="chemical">creatine</span> kinase level had returned to 230 IU / L and the patient was discharged . 