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: Further analysis of these data suggests that the duration of therapy , plasma aminoglycoside levels , liver disease , advanced age , high initial estimated creatinine clearance and , possibly , female gender all increase the risk for nephrotoxicity .
### Output Text:
Further analysis of these data suggests that the duration of therapy , plasma <span class="chemical">aminoglycoside</span> levels , liver disease , advanced age , high initial estimated <span class="chemical">creatinine</span> clearance and , possibly , female gender all increase the risk for nephrotoxicity . 