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: RESULTS : Gentamicin - treated rats presented a transitory increase in plasma creatinine levels .
### Output Text:
RESULTS : <span class="chemical">Gentamicin</span> - treated rats presented a transitory increase in plasma <span class="chemical">creatinine</span> levels . 