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: Torsade de pointes induced by metoclopramide in an elderly woman with preexisting complete left bundle branch block .
### Output Text:
Torsade de pointes induced by <span class="chemical">metoclopramide</span> in an elderly woman with preexisting complete left bundle branch block . 