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: It reduces the severity of " off " phase symptoms , improves the axial symptoms and reduces levodopa requirements .
### Output Text:
It reduces the severity of " off " phase symptoms , improves the axial symptoms and reduces <span class="chemical">levodopa</span> requirements . 