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: Patients with dyskinesia had lower onset age ( p < 0 . 001 ) , longer duration of levodopa therapy ( p < 0 . 001 ) , longer disease duration ( p < 0 . 001 ) , higher total daily levodopa dose ( p < 0 . 001 ) , and higher total UPDRS scores ( p = 0 . 005 ) than patients without dyskinesia .
### Output Text:
Patients with dyskinesia had lower onset age ( p < 0 . 001 ) , longer duration of <span class="chemical">levodopa</span> therapy ( p < 0 . 001 ) , longer disease duration ( p < 0 . 001 ) , higher total daily <span class="chemical">levodopa</span> dose ( p < 0 . 001 ) , and higher total UPDRS scores ( p = 0 . 005 ) than patients without dyskinesia . 