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: This study suggests that administration of low doses of beta - blockers may improve levodopa - induced ballistic and choreic dyskinesia in PD .
### Output Text:
This study suggests that administration of low doses of beta - blockers may improve <span class="chemical">levodopa</span> - induced ballistic and choreic dyskinesia in PD . 