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: BACKGROUND : Reports of severe bradyarrhythmia during amiodarone therapy are infrequent and limited to studies assessing the therapy ' s use in the management of patients with ventricular arrhythmias .
### Output Text:
BACKGROUND : Reports of severe bradyarrhythmia during <span class="chemical">amiodarone</span> therapy are infrequent and limited to studies assessing the therapy ' s use in the management of patients with ventricular arrhythmias . 