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: We conclude that levodopa has a central hypotensive action that parallels the motor effects in fluctuating patients .
### Output Text:
We conclude that <span class="chemical">levodopa</span> has a central hypotensive action that parallels the motor effects in fluctuating patients . 