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: Necrotising fasciitis after bortezomib and dexamethasone - containing regimen in an elderly patient of Waldenstrom macroglobulinaemia .
### Output Text:
Necrotising fasciitis after <span class="chemical">bortezomib</span> and <span class="chemical">dexamethasone</span> - containing regimen in an elderly patient of Waldenstrom macroglobulinaemia . 