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 conclude that , despite a relatively high incidence of adverse reactions , danazol has proven to be remarkably safe over the long - term in this group of patients .
### Output Text:
We conclude that , despite a relatively high incidence of adverse reactions , <span class="chemical">danazol</span> has proven to be remarkably safe over the long - term in this group of patients . 