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: Its occurrence in a patient being treated with imipramine is described , representing the first reported case of this syndrome in conjunction with antidepressants .
### Output Text:
Its occurrence in a patient being treated with <span class="chemical">imipramine</span> is described , representing the first reported case of this syndrome in conjunction with <span class="chemical">antidepressants</span> . 