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 the occurrence of a generalized tonic - clonic seizure in a pediatric patient following the administration of flumazenil .
### Output Text:
We report the occurrence of a generalized tonic - clonic seizure in a pediatric patient following the administration of <span class="chemical">flumazenil</span> . 