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: Dyskinesia was present in 44 % ( n = 42 ) with median levodopa therapy of 3 years .
### Output Text:
Dyskinesia was present in 44 % ( n = 42 ) with median <span class="chemical">levodopa</span> therapy of 3 years . 