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: Cisapride , a cytochrome P450 3A4 ( CYP3A4 ) substrate , is widely prescribed for the treatment of gastrointestinal motility disorders .
### Output Text:
<span class="chemical">Cisapride</span> , a cytochrome P450 3A4 ( CYP3A4 ) substrate , is widely prescribed for the treatment of gastrointestinal motility disorders . 