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: After exercise , ejection fraction was reduced at 15 and 30 minutes compared with baseline ( mean ( SEM ) , - 5 . 6 ( 1 . 5 ) % , p < 0 . 05 ; and - 6 . 1 ( 2 . 2 ) % , p < 0 . 01 ) , and at 30 and 45 minutes after dobutamine ( - 10 . 8 ( 1 . 8 ) % and - 5 . 5 ( 1 . 8 ) % , both p < 0 . 01 ) .
### Output Text:
After exercise , ejection fraction was reduced at 15 and 30 minutes compared with baseline ( mean ( SEM ) , - 5 . 6 ( 1 . 5 ) % , p < 0 . 05 ; and - 6 . 1 ( 2 . 2 ) % , p < 0 . 01 ) , and at 30 and 45 minutes after <span class="chemical">dobutamine</span> ( - 10 . 8 ( 1 . 8 ) % and - 5 . 5 ( 1 . 8 ) % , both p < 0 . 01 ) . 