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: METHODS : Following Food and Drug Administration and institutional review board approval and written informed consent , 65 volunteers were studied in two trials : an open - label , dose - escalating trial with intrathecal adenosine doses of 0 . 25 - 2 . 0 mg and a double - blind , placebo - controlled trial of adenosine , 2 mg .
### Output Text:
METHODS : Following Food and Drug Administration and institutional review board approval and written informed consent , 65 volunteers were studied in two trials : an open - label , dose - escalating trial with intrathecal <span class="chemical">adenosine</span> doses of 0 . 25 - 2 . 0 mg and a double - blind , placebo - controlled trial of <span class="chemical">adenosine</span> , 2 mg . 