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: OBJECTIVE : In vitro work has demonstrated that cinacalcet is a strong inhibitor of cytochrome P450 isoenzyme ( CYP ) 2D6 .
### Output Text:
OBJECTIVE : In vitro work has demonstrated that <span class="chemical">cinacalcet</span> is a strong inhibitor of cytochrome P450 isoenzyme ( CYP ) 2D6 . 