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: To gain insight into the mechanism of this unwanted effect , mice were administered various doses of amiodarone and examined for changes in hepatic histology and gene regulation .
### Output Text:
To gain insight into the mechanism of this unwanted effect , mice were administered various doses of <span class="chemical">amiodarone</span> and examined for changes in hepatic histology and gene regulation . 