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: The nitric oxide ( NO ) inhibitor nitro - L - arginine methyl ester ( L - NAME ) may act as an otoprotectant against high - frequency hearing loss caused by gentamicin , but further studies are needed to confirm this . Aminoglycoside antibiotics are still widely used by virtue of their efficacy and low cost .
### Output Text:
The <span class="chemical">nitric oxide</span> ( <span class="chemical">NO</span> ) inhibitor <span class="chemical">nitro - L - arginine methyl ester</span> ( <span class="chemical">L - NAME</span> ) may act as an otoprotectant against high - frequency hearing loss caused by <span class="chemical">gentamicin</span> , but further studies are needed to confirm this . <span class="chemical">Aminoglycoside</span> antibiotics are still widely used by virtue of their efficacy and low cost . 