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: We observed sinoatrial block due to chronic amiodarone administration in a 5 - year - old boy with primary cardiomyopathy , Wolff - Parkinson - White syndrome and supraventricular tachycardia .
### Output Text:
We observed sinoatrial block due to chronic <span class="chemical">amiodarone</span> administration in a 5 - year - old boy with primary cardiomyopathy , Wolff - Parkinson - White syndrome and supraventricular tachycardia . 