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: Gastrointestinal side effects from CPDD were universal .
### Output Text:
Gastrointestinal side effects from <span class="chemical">CPDD</span> were universal . 