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: Sixty - nine percent of patients continued treatment with amiodarone and had no recurrence of symptomatic VT or ventricular fibrillation ( VF ) over a follow - up of 6 to 52 months ( mean + / - standard deviation 14 . 2 + / - 8 . 2 ) .
### Output Text:
Sixty - nine percent of patients continued treatment with <span class="chemical">amiodarone</span> and had no recurrence of symptomatic VT or ventricular fibrillation ( VF ) over a follow - up of 6 to 52 months ( mean + / - standard deviation 14 . 2 + / - 8 . 2 ) . 