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: Also , digoxin has undesirable effects such as increasing peripheral resistance and myocardial demands , and causing arrhythmias .
### Output Text:
Also , <span class="chemical">digoxin</span> has undesirable effects such as increasing peripheral resistance and myocardial demands , and causing arrhythmias . 