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 aim of this study was to characterize the oropharyngeal dynamics in PD patients with and without levodopa - induced dyskinesia .
### Output Text:
The aim of this study was to characterize the oropharyngeal dynamics in PD patients with and without <span class="chemical">levodopa</span> - induced dyskinesia . 