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 45 min , 1 mg / kg bupivacaine was injected over 5 min , again followed by 4 micrograms . kg - 1 . min - 1 epinephrine .
### Output Text:
After 45 min , 1 mg / kg <span class="chemical">bupivacaine</span> was injected over 5 min , again followed by 4 micrograms . kg - 1 . min - 1 <span class="chemical">epinephrine</span> . 