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: This report of torsade de pointes ventricular tachycardia during intermittent dobutamine supports the hypothesis that unpredictable fatal arrhythmias may occur even with low doses and in patients with no history of significant rhythm disturbances .
### Output Text:
This report of torsade de pointes ventricular tachycardia during intermittent <span class="chemical">dobutamine</span> supports the hypothesis that unpredictable fatal arrhythmias may occur even with low doses and in patients with no history of significant rhythm disturbances . 