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: To evaluate amikacin - associated nephrotoxicity in an adult hematology / oncology population , a prospective , randomized , open - label trial was conducted at a university - affiliated medical center .
### Output Text:
To evaluate <span class="chemical">amikacin</span> - associated nephrotoxicity in an adult hematology / oncology population , a prospective , randomized , open - label trial was conducted at a university - affiliated medical center . 