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: We have described a unique patient who had reversible and dose - related myasthenia gravis after penicillamine and chloroquine therapy for rheumatoid arthritis .
### Output Text:
We have described a unique patient who had reversible and dose - related myasthenia gravis after <span class="chemical">penicillamine</span> and <span class="chemical">chloroquine</span> therapy for rheumatoid arthritis . 