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 rapid injection via the central venous route and the concomitant tapering of dopamine infusion might have contributed in precipitating the adverse drug reaction .
### Output Text:
The rapid injection via the central venous route and the concomitant tapering of <span class="chemical">dopamine</span> infusion might have contributed in precipitating the adverse drug reaction . 