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: These cases call attention to possible paranoid exacerbations with serotonin reuptake blockers in select patients and raise neurobiological considerations regarding paranoia .
### Output Text:
These cases call attention to possible paranoid exacerbations with <span class="chemical">serotonin</span> reuptake blockers in select patients and raise neurobiological considerations regarding paranoia . 