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: Because he was unable to discontinue nonsteroidal anti - inflammatory drug therapy , fludrocortisone was added , correcting the hyperkalemia and allowing indomethacin therapy to be continued safely .
### Output Text:
Because he was unable to discontinue nonsteroidal anti - inflammatory drug therapy , <span class="chemical">fludrocortisone</span> was added , correcting the hyperkalemia and allowing <span class="chemical">indomethacin</span> therapy to be continued safely . 