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: Our aim was to assess the effects of long - term treatment with a prokinetic agent , cisapride , on postprandial jejunal motility and symptoms in the irritable bowel syndrome ( IBS ) .
### Output Text:
Our aim was to assess the effects of long - term treatment with a prokinetic agent , <span class="chemical">cisapride</span> , on postprandial jejunal motility and symptoms in the irritable bowel syndrome ( IBS ) . 