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: OBJECTIVE : To report a case of fatal liver failure possibly associated with concurrent use of bupropion and carbimazole .
### Output Text:
OBJECTIVE : To report a case of fatal liver failure possibly associated with concurrent use of <span class="chemical">bupropion</span> and <span class="chemical">carbimazole</span> . 