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: OBJECTIVE : Nephrotoxicity is the major adverse effect of amphotericin B ( AmB ) , often limiting administration of full dosage .
### Output Text:
OBJECTIVE : Nephrotoxicity is the major adverse effect of <span class="chemical">amphotericin B</span> ( <span class="chemical">AmB</span> ) , often limiting administration of full dosage . 