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 combined administration of CSA and various chemotherapeutic drugs with a nephrotoxic potential , such as gentamicin ( at therapeutic doses ) , amphothericin B and ketoconazole , which are frequently used in immunosuppressed patients , did not aggravate the CSA induced toxicity in the rat model .
### Output Text:
The combined administration of <span class="chemical">CSA</span> and various chemotherapeutic drugs with a nephrotoxic potential , such as <span class="chemical">gentamicin</span> ( at therapeutic doses ) , <span class="chemical">amphothericin B</span> and <span class="chemical">ketoconazole</span> , which are frequently used in immunosuppressed patients , did not aggravate the <span class="chemical">CSA</span> induced toxicity in the rat model . 