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: METHODS : All patients taking Vigabatrin alone or in combination with other antiepileptic drugs for at least 5 years ( range 5 - 12 years ) were entered into a visual surveillance programme .
### Output Text:
METHODS : All patients taking <span class="chemical">Vigabatrin</span> alone or in combination with other antiepileptic drugs for at least 5 years ( range 5 - 12 years ) were entered into a visual surveillance programme . 