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: Chronic progesterone pretreatment ( 5 mg / kg / day for 21 days ) caused a significant increase in bupivacaine arrhythmogenicity in intact pentobarbital - anesthetized rats .
### Output Text:
Chronic <span class="chemical">progesterone</span> pretreatment ( 5 mg / kg / day for 21 days ) caused a significant increase in <span class="chemical">bupivacaine</span> arrhythmogenicity in intact <span class="chemical">pentobarbital</span> - anesthetized rats . 