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: Flumazenil ( mean dose , 0 . 76 mg ) or placebo ( mean dose , 8 . 9 ml ) was administered intravenously to 130 and 67 patients , respectively , who had been given diazepam in conjunction with an opioid ( fentanyl , meperidine , or morphine ) for the induction and maintenance of intravenous conscious sedation for diagnostic or therapeutic surgical procedures .
### Output Text:
<span class="chemical">Flumazenil</span> ( mean dose , 0 . 76 mg ) or placebo ( mean dose , 8 . 9 ml ) was administered intravenously to 130 and 67 patients , respectively , who had been given <span class="chemical">diazepam</span> in conjunction with an opioid ( <span class="chemical">fentanyl</span> , <span class="chemical">meperidine</span> , or <span class="chemical">morphine</span> ) for the induction and maintenance of intravenous conscious sedation for diagnostic or therapeutic surgical procedures . 