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: CONCLUSION : The MTD was calculated to be at 200 microg carbetocin .
### Output Text:
CONCLUSION : The MTD was calculated to be at 200 microg <span class="chemical">carbetocin</span> . 