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: Sprague - Dawley male rats ( 200 ~ 250 g ) were subcutaneously injected with gentamicin ( 100 mg / kg per day ) for 7 days , and the expression of tubular transporters was determined by immunoblotting and immunohistochemistry .
### Output Text:
Sprague - Dawley male rats ( 200 ~ 250 g ) were subcutaneously injected with <span class="chemical">gentamicin</span> ( 100 mg / kg per day ) for 7 days , and the expression of tubular transporters was determined by immunoblotting and immunohistochemistry . 