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: CONCLUSION : This small study suggests that a once - daily dosing regimen of tobramycin is at least as effective as and is no more and possibly less toxic than the twice - daily regimen .
### Output Text:
CONCLUSION : This small study suggests that a once - daily dosing regimen of <span class="chemical">tobramycin</span> is at least as effective as and is no more and possibly less toxic than the twice - daily regimen . 