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 beneficial effects of vitamin C administration to gentamicin - treated animals are also confirmed through : lower level of blood urea and creatinine and higher level of potassium .
### Output Text:
The beneficial effects of <span class="chemical">vitamin C</span> administration to <span class="chemical">gentamicin</span> - treated animals are also confirmed through : lower level of blood <span class="chemical">urea</span> and <span class="chemical">creatinine</span> and higher level of <span class="chemical">potassium</span> . 