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 mechanism responsible for this effect is unclear and paradoxical , considering the current evidence of a pulmonary hypertension protective fluoxetine effect in adult rodents .
### Output Text:
The mechanism responsible for this effect is unclear and paradoxical , considering the current evidence of a pulmonary hypertension protective <span class="chemical">fluoxetine</span> effect in adult rodents . 