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 purpose of this study was to evaluate the effect of cinacalcet on CYP2D6 activity , using desipramine as a probe substrate , in healthy subjects .
### Output Text:
The purpose of this study was to evaluate the effect of <span class="chemical">cinacalcet</span> on CYP2D6 activity , using <span class="chemical">desipramine</span> as a probe substrate , in healthy subjects . 