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: Tobramycin was given to a total daily dose of 300 mg / m2 and carbenicillin was given at a dose of 5 gm every four hours .
### Output Text:
<span class="chemical">Tobramycin</span> was given to a total daily dose of 300 mg / m2 and <span class="chemical">carbenicillin</span> was given at a dose of 5 gm every four hours . 