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: A 62 - year - old man was found to have bradycardia , hypothermia and respiratory failure 3 weeks after initiation of amiodarone therapy for atrial fibrillation .
### Output Text:
A 62 - year - old man was found to have bradycardia , hypothermia and respiratory failure 3 weeks after initiation of <span class="chemical">amiodarone</span> therapy for atrial fibrillation . 