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: Multiple side effects of penicillamine therapy in one patient with rheumatoid arthritis .
### Output Text:
Multiple side effects of <span class="chemical">penicillamine</span> therapy in one patient with rheumatoid arthritis . 