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: Forty - nine percent of patients were pain free 2 h after rizatriptan , compared with 24 . 3 % treated with ergotamine / caffeine ( p < or = 0 . 001 ) , rizatriptan being superior within 1 h of treatment .
### Output Text:
Forty - nine percent of patients were pain free 2 h after <span class="chemical">rizatriptan</span> , compared with 24 . 3 % treated with <span class="chemical">ergotamine</span> / <span class="chemical">caffeine</span> ( p < or = 0 . 001 ) , <span class="chemical">rizatriptan</span> being superior within 1 h of treatment . 