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: Dothiepin thus was found to be an effective antidepressant drug associated with fewer side effects than amitriptyline in the treatment of depressed outpatients .
### Output Text:
<span class="chemical">Dothiepin</span> thus was found to be an effective <span class="chemical">antidepressant</span> drug associated with fewer side effects than <span class="chemical">amitriptyline</span> in the treatment of depressed outpatients . 