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: During the 1 - hour study period , the incidence of central nervous system side effects was significantly greater in the lidocaine group , hypotension occurred in 11 patients , nine of whom had received lidocaine , and four patients died from asystole , three of whom had had lidocaine .
### Output Text:
During the 1 - hour study period , the incidence of central nervous system side effects was significantly greater in the <span class="chemical">lidocaine</span> group , hypotension occurred in 11 patients , nine of whom had received <span class="chemical">lidocaine</span> , and four patients died from asystole , three of whom had had <span class="chemical">lidocaine</span> . 