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: After in utero exposure to a low fluoxetine concentration the pulmonary arterial smooth muscle cell proliferation rate was significantly increased in fetal , but not adult , cells ( P < 0 . 01 ) .
### Output Text:
After in utero exposure to a low <span class="chemical">fluoxetine</span> concentration the pulmonary arterial smooth muscle cell proliferation rate was significantly increased in fetal , but not adult , cells ( P < 0 . 01 ) . 