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: Digoxin was the only other medication associated with an increased risk of pacemaker insertion ( OR : 1 . 78 , 95 % CI : 1 . 37 to 2 . 31 ) .
### Output Text:
<span class="chemical">Digoxin</span> was the only other medication associated with an increased risk of pacemaker insertion ( OR : 1 . 78 , 95 % CI : 1 . 37 to 2 . 31 ) . 