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: Maximal cTnI ( pg / ml ) and cTnT levels were significantly increased in DOX rats compared with controls ( p = 0 . 006 , 0 . 007 ) .
### Output Text:
Maximal cTnI ( pg / ml ) and cTnT levels were significantly increased in <span class="chemical">DOX</span> rats compared with controls ( p = 0 . 006 , 0 . 007 ) . 