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: RESULTS : During treatment , 11 patients showed a reduction in sural nerve SAP amplitude compared to baseline values ( 9 with a reduction > or = 50 % and 2 < 50 % ) .
### Output Text:
RESULTS : During treatment , 11 patients showed a reduction in sural nerve SAP amplitude compared to baseline values ( 9 with a reduction > or = 50 % and 2 < 50 % ) . 