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: Torsade de pointes ventricular tachycardia during low dose intermittent dobutamine treatment in a patient with dilated cardiomyopathy and congestive heart failure .
### Output Text:
Torsade de pointes ventricular tachycardia during low dose intermittent <span class="chemical">dobutamine</span> treatment in a patient with dilated cardiomyopathy and congestive heart failure . 