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: One week prior to admission a therapy with standard doses of metoprolol ( 100 mg t . i . d . and then 100 mg b . i . d . ) had been initiated .
### Output Text:
One week prior to admission a therapy with standard doses of <span class="chemical">metoprolol</span> ( 100 mg t . i . d . and then 100 mg b . i . d . ) had been initiated . 