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 study ' s aims were to measure variations in sural nerve sensory action potential ( SAP ) amplitude in patients with refractory cutaneous lupus erythematosus ( CLE ) treated with thalidomide and use these findings to identify the neurotoxic potential of thalidomide and the recovery capacity of sensory fibres after discontinuation of treatment .
### Output Text:
The study ' s aims were to measure variations in sural nerve sensory action potential ( SAP ) amplitude in patients with refractory cutaneous lupus erythematosus ( CLE ) treated with <span class="chemical">thalidomide</span> and use these findings to identify the neurotoxic potential of <span class="chemical">thalidomide</span> and the recovery capacity of sensory fibres after discontinuation of treatment . 