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 authors describe the case of a 56 - year - old woman with chronic , severe heart failure secondary to dilated cardiomyopathy and absence of significant ventricular arrhythmias who developed QT prolongation and torsade de pointes ventricular tachycardia during one cycle of intermittent low dose ( 2 . 5 mcg / kg per min ) dobutamine .
### Output Text:
The authors describe the case of a 56 - year - old woman with chronic , severe heart failure secondary to dilated cardiomyopathy and absence of significant ventricular arrhythmias who developed QT prolongation and torsade de pointes ventricular tachycardia during one cycle of intermittent low dose ( 2 . 5 mcg / kg per min ) <span class="chemical">dobutamine</span> . 