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: Pain on injection ( 80 vs . 20 % , p < 0 . 01 ) and thrombophlebitis ( 93 . 3 vs . 6 . 6 % , p < 0 . 001 ) occurred more frequently with AM149 than with Disoprivan .
### Output Text:
Pain on injection ( 80 vs . 20 % , p < 0 . 01 ) and thrombophlebitis ( 93 . 3 vs . 6 . 6 % , p < 0 . 001 ) occurred more frequently with AM149 than with <span class="chemical">Disoprivan</span> . 