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: An unusual toxic reaction to axillary block by mepivacaine with adrenaline .
### Output Text:
An unusual toxic reaction to axillary block by <span class="chemical">mepivacaine</span> with <span class="chemical">adrenaline</span> . 