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 convulsant activity of bupivacaine was not significantly modified but calcium channel blockers decreased the time of latency to obtain bupivacaine - induced convulsions ; this effect was less pronounced with bepridil .
### Output Text:
The convulsant activity of <span class="chemical">bupivacaine</span> was not significantly modified but <span class="chemical">calcium</span> channel blockers decreased the time of latency to obtain <span class="chemical">bupivacaine</span> - induced convulsions ; this effect was less pronounced with <span class="chemical">bepridil</span> . 