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: CONCLUSION : Despite theoretical concerns that lidocaine may enhance cocaine toxicity , the use of lidocaine in patients with cocaine - associated MI was not associated with significant cardiovascular or central nervous system toxicity .
### Output Text:
CONCLUSION : Despite theoretical concerns that <span class="chemical">lidocaine</span> may enhance <span class="chemical">cocaine</span> toxicity , the use of <span class="chemical">lidocaine</span> in patients with <span class="chemical">cocaine</span> - associated MI was not associated with significant cardiovascular or central nervous system toxicity . 