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: Further observations on the electrophysiologic effects of oral amiodarone therapy .
### Output Text:
Further observations on the electrophysiologic effects of oral <span class="chemical">amiodarone</span> therapy . 