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: Pooled analysis of the effects of other inotropic drugs shows an excess mortality and there is a possibility that digoxin may increase mortality after myocardial infarction ( MI ) .
### Output Text:
Pooled analysis of the effects of other inotropic drugs shows an excess mortality and there is a possibility that <span class="chemical">digoxin</span> may increase mortality after myocardial infarction ( MI ) . 