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 average hearing loss for speech frequencies was about 10 dB after prilocaine and 15 dB after bupivacaine .
### Output Text:
The average hearing loss for speech frequencies was about 10 dB after <span class="chemical">prilocaine</span> and 15 dB after <span class="chemical">bupivacaine</span> . 