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: In this study we postulated that during acute renal failure induced by gentamicin the transient or dynamic response of blood vessels could be affected , and that antioxidants can prevent the changes in dynamic responses of blood vessels .
### Output Text:
In this study we postulated that during acute renal failure induced by <span class="chemical">gentamicin</span> the transient or dynamic response of blood vessels could be affected , and that antioxidants can prevent the changes in dynamic responses of blood vessels . 