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: Seven patients suffering from Parkinson ' s disease ( PD ) with severely disabling dyskinesia received low - dose propranolol as an adjunct to the currently used medical treatment .
### Output Text:
Seven patients suffering from Parkinson ' s disease ( PD ) with severely disabling dyskinesia received low - dose <span class="chemical">propranolol</span> as an adjunct to the currently used medical treatment . 