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: The findings indicate that thalidomide may be an option for patients who have failed other forms of therapy , provided close follow - up is maintained for development of peripheral neuropathy .
### Output Text:
The findings indicate that <span class="chemical">thalidomide</span> may be an option for patients who have failed other forms of therapy , provided close follow - up is maintained for development of peripheral neuropathy . 