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: PATIENTS AND METHODS : Clinical and electrophysiological data in 12 female patients with CLE during treatment with thalidomide and up to 47 months after discontinuation of treatment were analysed .
### Output Text:
PATIENTS AND METHODS : Clinical and electrophysiological data in 12 female patients with CLE during treatment with <span class="chemical">thalidomide</span> and up to 47 months after discontinuation of treatment were analysed . 