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: Complicated depressive disorders ( including atypicality of course and symptomatology , chronicity , psychosis , bipolarity , and secondary onset in the course of a primary psychosis ) may present particular vulnerability to paranoid exacerbations associated with serotonin reuptake inhibitors .
### Output Text:
Complicated depressive disorders ( including atypicality of course and symptomatology , chronicity , psychosis , bipolarity , and secondary onset in the course of a primary psychosis ) may present particular vulnerability to paranoid exacerbations associated with <span class="chemical">serotonin</span> reuptake inhibitors . 