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: Reduction in the dosage of amiodarone resulted in the disappearance of the sinoatrial block and the persistence of asymptomatic sinus bradycardia .
### Output Text:
Reduction in the dosage of <span class="chemical">amiodarone</span> resulted in the disappearance of the sinoatrial block and the persistence of asymptomatic sinus bradycardia . 