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: DISCUSSION : Drug - induced symptoms of pheochromocytoma are often associated with the use of substituted benzamide drugs , but the underlying mechanism is unknown .
### Output Text:
DISCUSSION : Drug - induced symptoms of pheochromocytoma are often associated with the use of substituted <span class="chemical">benzamide</span> drugs , but the underlying mechanism is unknown . 