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: The daily dose ( initial dose : 1 mg ; mean dose at the end of the trial : 4 . 47 mg ) was always administered in one single dose .
### Output Text:
The daily dose ( initial dose : 1 mg ; mean dose at the end of the trial : 4 . 47 mg ) was always administered in one single dose . 