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: Between July 2001 and April 2004 , 24 patients with relapsed / refractory indolent lymphomas received thalidomide 200 mg daily with escalation by 100 mg daily every 1 - 2 weeks as tolerated , up to a maximum of 800 mg daily .
### Output Text:
Between July 2001 and April 2004 , 24 patients with relapsed / refractory indolent lymphomas received <span class="chemical">thalidomide</span> 200 mg daily with escalation by 100 mg daily every 1 - 2 weeks as tolerated , up to a maximum of 800 mg daily . 