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: After determining the bupivacaine AD50 ( the concentration of bupivacaine that caused 50 % of all beating rat heart myocyte cultures to become arrhythmic ) , we determined the effect of 1 - hour progesterone HCl exposure on myocyte contractile rhythm .
### Output Text:
After determining the <span class="chemical">bupivacaine</span> AD50 ( the concentration of <span class="chemical">bupivacaine</span> that caused 50 % of all beating rat heart myocyte cultures to become arrhythmic ) , we determined the effect of 1 - hour <span class="chemical">progesterone</span> <span class="chemical">HCl</span> exposure on myocyte contractile rhythm . 