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: Six percent of the patients had a nonfatal recurrence of VT and were successfully managed by continuing amiodarone at a higher dose or by the addition of a conventional antiarrhythmic drug .
### Output Text:
Six percent of the patients had a nonfatal recurrence of VT and were successfully managed by continuing <span class="chemical">amiodarone</span> at a higher dose or by the addition of a conventional antiarrhythmic drug . 