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: Long - term efficacy and toxicity of high - dose amiodarone therapy for ventricular tachycardia or ventricular fibrillation .
### Output Text:
Long - term efficacy and toxicity of high - dose <span class="chemical">amiodarone</span> therapy for ventricular tachycardia or ventricular fibrillation . 