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: Higher doses of AMN082 ( 10 and 20 mg / kg p . o . ) have no effect on the same models of PD .
### Output Text:
Higher doses of <span class="chemical">AMN082</span> ( 10 and 20 mg / kg p . o . ) have no effect on the same models of PD . 