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: The results of this study indicate that progesterone can potentiate bupivacaine arrhythmogenicity both in vivo and in vitro .
### Output Text:
The results of this study indicate that <span class="chemical">progesterone</span> can potentiate <span class="chemical">bupivacaine</span> arrhythmogenicity both in vivo and in vitro . 