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 mean plasma lidocaine level of patients on beta - blocking agents was no different from that in patients not on beta blocking agents .
### Output Text:
The mean plasma <span class="chemical">lidocaine</span> level of patients on beta - blocking agents was no different from that in patients not on beta blocking agents . 