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: METHODS : Following induction of anesthesia by fentanyl ( 0 . 15 mg kg ( - 1 ) ) and propofol ( 2 . 0 mg kg ( - 1 ) ) , 13 patients received phenylephrine ( 0 . 1 mg iv ) and 12 patients received ephedrine ( 10 mg iv ) to restore mean arterial pressure ( MAP ) .
### Output Text:
METHODS : Following induction of anesthesia by <span class="chemical">fentanyl</span> ( 0 . 15 mg kg ( - 1 ) ) and <span class="chemical">propofol</span> ( 2 . 0 mg kg ( - 1 ) ) , 13 patients received <span class="chemical">phenylephrine</span> ( 0 . 1 mg iv ) and 12 patients received <span class="chemical">ephedrine</span> ( 10 mg iv ) to restore mean arterial pressure ( MAP ) . 