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: Doxorubicin toxicokinetics studies revealed no change in accumulation of doxorubicin and doxorubicinol ( toxic metabolite ) in the normal diet - fed ( ND ) and OB hearts .
### Output Text:
<span class="chemical">Doxorubicin</span> toxicokinetics studies revealed no change in accumulation of <span class="chemical">doxorubicin</span> and <span class="chemical">doxorubicinol</span> ( toxic metabolite ) in the normal diet - fed ( ND ) and OB hearts . 