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: Both dronedarone and amiodarone significantly reduced the exercise - induced tachycardia and , at the highest dose , decreased the isoproterenol - induced tachycardia .
### Output Text:
Both <span class="chemical">dronedarone</span> and <span class="chemical">amiodarone</span> significantly reduced the exercise - induced tachycardia and , at the highest dose , decreased the <span class="chemical">isoproterenol</span> - induced tachycardia . 