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: Depending on the drugs that would be given before the induction of anesthesia with etomidate , the patients were separated into 4 groups : no pretreatment ( Group NP ) , fentanyl 1 ug . kg - 1 ( Group F ) , midazolam 0 . 03 mg . kg - 1 ( Group M ) , and midazolam 0 . 015 mg . kg - 1 + fentanyl 0 . 5 ug . kg - 1 ( Group FM ) .
### Output Text:
Depending on the drugs that would be given before the induction of anesthesia with <span class="chemical">etomidate</span> , the patients were separated into 4 groups : no pretreatment ( Group NP ) , <span class="chemical">fentanyl</span> 1 ug . kg - 1 ( Group F ) , <span class="chemical">midazolam</span> 0 . 03 mg . kg - 1 ( Group M ) , and <span class="chemical">midazolam</span> 0 . 015 mg . kg - 1 + <span class="chemical">fentanyl</span> 0 . 5 ug . kg - 1 ( Group FM ) . 