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: The overall incidence of side effects and the frequency and severity of blurred vision , dry mouth , and drowsiness were significantly less with dothiepin than with amitriptyline .
### Output Text:
The overall incidence of side effects and the frequency and severity of blurred vision , dry mouth , and drowsiness were significantly less with <span class="chemical">dothiepin</span> than with <span class="chemical">amitriptyline</span> . 