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: When coadministered with AZT from the onset of drug administration , BAU reduced AZT - induced marrow toxicity .
### Output Text:
When coadministered with <span class="chemical">AZT</span> from the onset of drug administration , <span class="chemical">BAU</span> reduced <span class="chemical">AZT</span> - induced marrow toxicity . 