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: Of the 12 patients considered for oral ursodeoxycholic acid ( UDCA ) treatment , two had a blocked cystic duct and were not started on UDCA while one was lost to follow up .
### Output Text:
Of the 12 patients considered for oral <span class="chemical">ursodeoxycholic acid</span> ( <span class="chemical">UDCA</span> ) treatment , two had a blocked cystic duct and were not started on <span class="chemical">UDCA</span> while one was lost to follow up . 