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: Pharmacokinetic interactions of curcumin with phenobarbitone and carbamazepine were also studied .
### Output Text:
Pharmacokinetic interactions of <span class="chemical">curcumin</span> with <span class="chemical">phenobarbitone</span> and <span class="chemical">carbamazepine</span> were also studied . 