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: This case report carries an important clinical application given the frequent usage of amiodarone among CHF patients .
### Output Text:
This case report carries an important clinical application given the frequent usage of <span class="chemical">amiodarone</span> among CHF patients . 