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 possible utility of chronic CBZ in preventing the development of toxic side effects in human cocaine users is suggested by these data , but remains to be directly evaluated .
### Output Text:
The possible utility of chronic <span class="chemical">CBZ</span> in preventing the development of toxic side effects in human <span class="chemical">cocaine</span> users is suggested by these data , but remains to be directly evaluated . 