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: Chronic pulsatile levodopa therapy for Parkinson ' s disease ( PD ) leads to the development of motor fluctuations and dyskinesia .
### Output Text:
Chronic pulsatile <span class="chemical">levodopa</span> therapy for Parkinson ' s disease ( PD ) leads to the development of motor fluctuations and dyskinesia . 