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: Taken together , these results extend previous studies and demonstrate that cocaine - induced cardiac dysfunction may be due to a mitochondrial defect .
### Output Text:
Taken together , these results extend previous studies and demonstrate that <span class="chemical">cocaine</span> - induced cardiac dysfunction may be due to a mitochondrial defect . 