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: This report describes a case of encephalopathy developed in the course of amitriptyline therapy , during a remission of unipolar depression .
### Output Text:
This report describes a case of encephalopathy developed in the course of <span class="chemical">amitriptyline</span> therapy , during a remission of unipolar depression . 