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: Lifetime treatment of mice with azidothymidine ( AZT ) produces myelodysplasia .
### Output Text:
Lifetime treatment of mice with <span class="chemical">azidothymidine</span> ( <span class="chemical">AZT</span> ) produces myelodysplasia . 