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: We propose that amphotericin , in the setting of reduced effective arterial volume , may activate tubuloglomerular feedback , thereby contributing to acute renal failure .
### Output Text:
We propose that <span class="chemical">amphotericin</span> , in the setting of reduced effective arterial volume , may activate tubuloglomerular feedback , thereby contributing to acute renal failure . 