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: Over the first 3 weeks after the i . v . administration of free and polymer - bound DOX , all animals showed a transient reduction in body weight .
### Output Text:
Over the first 3 weeks after the i . v . administration of free and polymer - bound <span class="chemical">DOX</span> , all animals showed a transient reduction in body weight . 