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: The possibility of a clinically relevant dopamine - antagonistic capacity of fluoxetine in Parkinson ' s disease patients must be considered .
### Output Text:
The possibility of a clinically relevant <span class="chemical">dopamine</span> - antagonistic capacity of <span class="chemical">fluoxetine</span> in Parkinson ' s disease patients must be considered . 