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: In conclusion , where succinylcholine is used , lidocaine is proven to be the useful pretreatment agent for the reduction of postoperative myalgia .
### Output Text:
In conclusion , where <span class="chemical">succinylcholine</span> is used , <span class="chemical">lidocaine</span> is proven to be the useful pretreatment agent for the reduction of postoperative myalgia . 