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 therefore investigated the long - term safety of danazol by performing a retrospective chart review of 60 female patients with hereditary angioedema treated with danazol for a continuous period of 6 months or longer .
### Output Text:
We therefore investigated the long - term safety of <span class="chemical">danazol</span> by performing a retrospective chart review of 60 female patients with hereditary angioedema treated with <span class="chemical">danazol</span> for a continuous period of 6 months or longer . 