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: However , the use of CBDCA higher - intensity schedules and the association with other neurotoxic drugs in polychemotherapy may cause some concern about its safety with respect to peripheral nervous system damage .
### Output Text:
However , the use of <span class="chemical">CBDCA</span> higher - intensity schedules and the association with other neurotoxic drugs in polychemotherapy may cause some concern about its safety with respect to peripheral nervous system damage . 