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: These data give support to the hypothesis that the pathogenesis of Vigabatrin - associated visual field defects may be an idiosyncratic adverse drug reaction rather than dose - dependent toxicity .
### Output Text:
These data give support to the hypothesis that the pathogenesis of <span class="chemical">Vigabatrin</span> - associated visual field defects may be an idiosyncratic adverse drug reaction rather than dose - dependent toxicity . 