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: Ten consecutive patients ( mean age , 58 . 4 + / - 6 . 8 years ; 7 men , 3 women ) with similar characteristics at the duration of disease ( mean disease time , 8 . 4 + / - 3 . 5 years ) , disabling motor fluctuations ( Hoehn _ Yahr stage 3 - 5 in off - drug phases ) and levodopa - induced dyskinesias were selected .
### Output Text:
Ten consecutive patients ( mean age , 58 . 4 + / - 6 . 8 years ; 7 men , 3 women ) with similar characteristics at the duration of disease ( mean disease time , 8 . 4 + / - 3 . 5 years ) , disabling motor fluctuations ( Hoehn _ Yahr stage 3 - 5 in off - drug phases ) and <span class="chemical">levodopa</span> - induced dyskinesias were selected . 