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: Curcumin co - administration did not cause any significant alteration in the serum concentrations of both phenobarbitone as well as carbamazepine .
### Output Text:
<span class="chemical">Curcumin</span> co - administration did not cause any significant alteration in the serum concentrations of both <span class="chemical">phenobarbitone</span> as well as <span class="chemical">carbamazepine</span> . 