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: Patients with this response more often had a history of hypertension and had higher resting systolic and diastolic BP before dobutamine infusion .
### Output Text:
Patients with this response more often had a history of hypertension and had higher resting systolic and diastolic BP before <span class="chemical">dobutamine</span> infusion . 