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: RESULTS : In diarrhoea - predominant patients significant differences in contraction characteristics were observed between the cisapride and placebo groups .
### Output Text:
RESULTS : In diarrhoea - predominant patients significant differences in contraction characteristics were observed between the <span class="chemical">cisapride</span> and placebo groups . 