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: This patient also developed torsade de pointes when cisapride and erythromycin were given simultaneously .
### Output Text:
This patient also developed torsade de pointes when <span class="chemical">cisapride</span> and <span class="chemical">erythromycin</span> were given simultaneously . 