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: Ventricular tachyarrhythmias during cesarean section after ritodrine therapy : interaction with anesthetics .
### Output Text:
Ventricular tachyarrhythmias during cesarean section after <span class="chemical">ritodrine</span> therapy : interaction with anesthetics . 