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: Acute renal insufficiency after high - dose melphalan in patients with primary systemic amyloidosis during stem cell transplantation .
### Output Text:
Acute renal insufficiency after high - dose <span class="chemical">melphalan</span> in patients with primary systemic amyloidosis during stem cell transplantation . 