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: We report syncope and bradycardia in an 11 - year - old girl following administration of intranasal dexmedetomidine for sedation for a voiding cystourethrogram .
### Output Text:
We report syncope and bradycardia in an 11 - year - old girl following administration of intranasal <span class="chemical">dexmedetomidine</span> for sedation for a voiding cystourethrogram . 