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: Data from 60 patients treated with amikacin were analyzed for factors associated with nephrotoxicity .
### Output Text:
Data from 60 patients treated with <span class="chemical">amikacin</span> were analyzed for factors associated with nephrotoxicity . 