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: Oral procaterol 50 micrograms b . d . , procaterol 100 micrograms b . d . , and terbutaline 5 mg t . i . d . , were compared when given randomly in 1 - week treatment periods .
### Output Text:
Oral <span class="chemical">procaterol</span> 50 micrograms b . d . , <span class="chemical">procaterol</span> 100 micrograms b . d . , and <span class="chemical">terbutaline</span> 5 mg t . i . d . , were compared when given randomly in 1 - week treatment periods . 