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: METHODS : Thirty - eight patients with IBS ( constipation - predominant , n = 17 ; diarrhoea - predominant , n = 21 ) underwent 24 - h ambulatory jejunal manometry before and after 12 week ' s treatment [ cisapride , 5 mg three times daily ( n = 19 ) or placebo ( n = 19 ) ] .
### Output Text:
METHODS : Thirty - eight patients with IBS ( constipation - predominant , n = 17 ; diarrhoea - predominant , n = 21 ) underwent 24 - h ambulatory jejunal manometry before and after 12 week ' s treatment [ <span class="chemical">cisapride</span> , 5 mg three times daily ( n = 19 ) or placebo ( n = 19 ) ] . 