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: Prolongation of the QT interval related to cisapride - diltiazem interaction .
### Output Text:
Prolongation of the QT interval related to <span class="chemical">cisapride</span> - <span class="chemical">diltiazem</span> interaction . 