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: These data suggest that during concomitant treatment with cinacalcet , dose adjustment may be necessary for drugs that demonstrate a narrow therapeutic index and are metabolized by CYP2D6 .
### Output Text:
These data suggest that during concomitant treatment with <span class="chemical">cinacalcet</span> , dose adjustment may be necessary for drugs that demonstrate a narrow therapeutic index and are metabolized by CYP2D6 . 