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: A repeat work - up revealed further elevations in aminotransferase levels , and liver biopsy revealed evidence of moderate - to - severe drug toxicity .
### Output Text:
A repeat work - up revealed further elevations in aminotransferase levels , and liver biopsy revealed evidence of moderate - to - severe drug toxicity . 