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 differential effects of CBZ depending upon stage of seizure development suggest that distinct mechanisms underlie the development versus maintenance of local anesthetic - kindled seizures .
### Output Text:
The differential effects of <span class="chemical">CBZ</span> depending upon stage of seizure development suggest that distinct mechanisms underlie the development versus maintenance of local anesthetic - kindled seizures . 