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: We report the increased amount of motor disability in four patients with idiopathic Parkinson ' s disease after exposure to the antidepressant fluoxetine .
### Output Text:
We report the increased amount of motor disability in four patients with idiopathic Parkinson ' s disease after exposure to the <span class="chemical">antidepressant</span> <span class="chemical">fluoxetine</span> . 