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: Headache relief at 2 h was 75 . 9 % for rizatriptan and 47 . 3 % for ergotamine / caffeine ( p < or = 0 . 001 ) , with rizatriptan being superior to ergotamine / caffeine within 30 min of dosing .
### Output Text:
Headache relief at 2 h was 75 . 9 % for <span class="chemical">rizatriptan</span> and 47 . 3 % for <span class="chemical">ergotamine</span> / <span class="chemical">caffeine</span> ( p < or = 0 . 001 ) , with <span class="chemical">rizatriptan</span> being superior to <span class="chemical">ergotamine</span> / <span class="chemical">caffeine</span> within 30 min of dosing . 