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: Antagonism between interleukin 3 and erythropoietin in mice with azidothymidine - induced anemia and in bone marrow endothelial cells .
### Output Text:
Antagonism between interleukin 3 and erythropoietin in mice with <span class="chemical">azidothymidine</span> - induced anemia and in bone marrow endothelial cells . 