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: A double - blind study of the efficacy and safety of dothiepin hydrochloride in the treatment of major depressive disorder .
### Output Text:
A double - blind study of the efficacy and safety of <span class="chemical">dothiepin hydrochloride</span> in the treatment of major depressive disorder . 