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: Consistent with other reports this case of TdP occurred in the context of multiple exacerbating factors including hypokalemia and digoxin excess .
### Output Text:
Consistent with other reports this case of TdP occurred in the context of multiple exacerbating factors including hypokalemia and <span class="chemical">digoxin</span> excess . 