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 cumulative doses of levobupivacaine that produced dysrhythmias and asystole were smaller than the corresponding doses of ropivacaine , but they were larger than those of bupivacaine .
### Output Text:
The cumulative doses of <span class="chemical">levobupivacaine</span> that produced dysrhythmias and asystole were smaller than the corresponding doses of <span class="chemical">ropivacaine</span> , but they were larger than those of <span class="chemical">bupivacaine</span> . 