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: CONCLUSION : Pretreatment with remifentanil 1 microg / kg reduced myoclonus after etomidate induction without side effects such as sedation , apnea , nausea , or pruritus .
### Output Text:
CONCLUSION : Pretreatment with <span class="chemical">remifentanil</span> 1 microg / kg reduced myoclonus after <span class="chemical">etomidate</span> induction without side effects such as sedation , apnea , nausea , or pruritus . 