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 highly - selective alpha - 2 adrenergic agonist dexmedetomidine ( D - MED ) is capable of inducing muscle flaccidity and anesthesia in rats and dogs .
### Output Text:
The highly - selective alpha - 2 adrenergic agonist <span class="chemical">dexmedetomidine</span> ( <span class="chemical">D - MED</span> ) is capable of inducing muscle flaccidity and anesthesia in rats and dogs . 