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: Nine days later the patient ' s creatine kinase had dropped to 1695 U / L and creatinine was 3 . 3 mg / dL .
### Output Text:
Nine days later the patient ' s <span class="chemical">creatine</span> kinase had dropped to 1695 U / L and <span class="chemical">creatinine</span> was 3 . 3 mg / dL . 