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: Our data also suggest that significant etoposide dose escalation is perhaps possible by the use of dexrazoxane .
### Output Text:
Our data also suggest that significant <span class="chemical">etoposide</span> dose escalation is perhaps possible by the use of <span class="chemical">dexrazoxane</span> . 