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: Because of the theoretical concern regarding administration of dobutamine in the setting of cocaine use , we conducted a pilot study to assess the safety of DSE in emergency department patients with cocaine - associated chest pain .
### Output Text:
Because of the theoretical concern regarding administration of <span class="chemical">dobutamine</span> in the setting of <span class="chemical">cocaine</span> use , we conducted a pilot study to assess the safety of DSE in emergency department patients with <span class="chemical">cocaine</span> - associated chest pain . 