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: In this study , 62 patients with confirmed initial normal renal function and treated with 2 to 5 mg / kg / day of gentamicin sulfate or tobramycin sulfate for a minimum of seven days were followed up prospectively for the development of aminoglycoside - related renal failure , defined as at least a one - third reduction in renal function .
### Output Text:
In this study , 62 patients with confirmed initial normal renal function and treated with 2 to 5 mg / kg / day of <span class="chemical">gentamicin sulfate</span> or <span class="chemical">tobramycin sulfate</span> for a minimum of seven days were followed up prospectively for the development of <span class="chemical">aminoglycoside</span> - related renal failure , defined as at least a one - third reduction in renal function . 