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: RESULTS : The prolactin levels of castrated and noncastrated groups treated with fluoxetine were statistically significantly higher when compared to their respective control groups .
### Output Text:
RESULTS : The prolactin levels of castrated and noncastrated groups treated with <span class="chemical">fluoxetine</span> were statistically significantly higher when compared to their respective control groups . 