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: Differential effects of systemically administered ketamine and lidocaine on dynamic and static hyperalgesia induced by intradermal capsaicin in humans .
### Output Text:
Differential effects of systemically administered <span class="chemical">ketamine</span> and <span class="chemical">lidocaine</span> on dynamic and static hyperalgesia induced by intradermal <span class="chemical">capsaicin</span> in humans . 