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: Twenty - three of the patients had previously taken appetite suppressants , mainly fenfluramines , as compared with only 5 of the controls ( 66 versus 6 % , p < 0 . 0001 ) .
### Output Text:
Twenty - three of the patients had previously taken <span class="chemical">appetite suppressants</span> , mainly <span class="chemical">fenfluramines</span> , as compared with only 5 of the controls ( 66 versus 6 % , p < 0 . 0001 ) . 