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: In the placebo group , male patients were associated with significantly increased incidence of myoclonus after etomidate administration .
### Output Text:
In the placebo group , male patients were associated with significantly increased incidence of myoclonus after <span class="chemical">etomidate</span> administration . 