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 pain score for buffered lidocaine was significantly lower than the mean score for standard lidocaine ( 2 . 7 + / - 1 . 9 vs . 3 . 8 + / - 2 . 2 , P = 0 . 03 ) .
### Output Text:
The mean pain score for buffered <span class="chemical">lidocaine</span> was significantly lower than the mean score for standard <span class="chemical">lidocaine</span> ( 2 . 7 + / - 1 . 9 vs . 3 . 8 + / - 2 . 2 , P = 0 . 03 ) . 