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 coronary spasm may be the cause of cardiotoxicity due to 5 - FU , and that calcium antagonists may probably be used in the prevention or treatment of 5 - FU cardiotoxicity .
### Output Text:
These data suggest that coronary spasm may be the cause of cardiotoxicity due to <span class="chemical">5 - FU</span> , and that <span class="chemical">calcium</span> antagonists may probably be used in the prevention or treatment of <span class="chemical">5 - FU</span> cardiotoxicity . 