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: While withdrawal of amiodarone leads to clinical improvement in majority of cases , this is not always possible or advisable .
### Output Text:
While withdrawal of <span class="chemical">amiodarone</span> leads to clinical improvement in majority of cases , this is not always possible or advisable . 