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: Previous anecdotal reports have linked creatine to the development of arrhythmia .
### Output Text:
Previous anecdotal reports have linked <span class="chemical">creatine</span> to the development of arrhythmia . 