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### Input Text: Clinical tolerability of both agents has been good , with fewer than 3 % of patients withdrawn from treatment because of clinical adverse experiences .
### Output Text:
Clinical tolerability of both agents has been good , with fewer than 3 % of patients withdrawn from treatment because of clinical adverse experiences . 