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 differential effects of ketamine and lidocaine on static and dynamic hyperalgesia suggest that the two types of hyperalgesia are mediated by separate mechanisms and have a distinct pharmacology .
### Output Text:
The differential effects of <span class="chemical">ketamine</span> and <span class="chemical">lidocaine</span> on static and dynamic hyperalgesia suggest that the two types of hyperalgesia are mediated by separate mechanisms and have a distinct pharmacology . 