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: Patients who received the same anesthetic procedure were selected : 2 minutes after intravenous injections of the pretreatment drugs , anesthesia is induced with 0 . 3 mg . kg - 1 etomidate injected intravenously over a period of 20 - 30 seconds .
### Output Text:
Patients who received the same anesthetic procedure were selected : 2 minutes after intravenous injections of the pretreatment drugs , anesthesia is induced with 0 . 3 mg . kg - 1 <span class="chemical">etomidate</span> injected intravenously over a period of 20 - 30 seconds . 