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: An interaction between FZP and pentylenetetrazol ( PTZ ) was shown by pretreating mice with FZP before PTZ challenge .
### Output Text:
An interaction between <span class="chemical">FZP</span> and <span class="chemical">pentylenetetrazol</span> ( <span class="chemical">PTZ</span> ) was shown by pretreating mice with <span class="chemical">FZP</span> before <span class="chemical">PTZ</span> challenge . 