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: Six healthy subjects were given a 0 . 5 mg subcutaneous dose of terbutaline on two occasions : 1 hour after oral administration of a placebo and 1 hour after 80 mg oxprenolol orally .
### Output Text:
Six healthy subjects were given a 0 . 5 mg subcutaneous dose of <span class="chemical">terbutaline</span> on two occasions : 1 hour after oral administration of a placebo and 1 hour after 80 mg <span class="chemical">oxprenolol</span> orally . 