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 magnitude of the hypotensive effect of levodopa was concentration dependent and was fit to an Emax model in fluctuating responders .
### Output Text:
The magnitude of the hypotensive effect of <span class="chemical">levodopa</span> was concentration dependent and was fit to an Emax model in fluctuating responders . 