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: The most common adverse events ( incidence > or = 5 % in one group ) after rizatriptan and ergotamine / caffeine , respectively , were dizziness ( 6 . 7 and 5 . 3 % ) , nausea ( 4 . 2 and 8 . 5 % ) and somnolence ( 5 . 5 and 2 . 3 % ) .
### Output Text:
The most common adverse events ( incidence > or = 5 % in one group ) after <span class="chemical">rizatriptan</span> and <span class="chemical">ergotamine</span> / <span class="chemical">caffeine</span> , respectively , were dizziness ( 6 . 7 and 5 . 3 % ) , nausea ( 4 . 2 and 8 . 5 % ) and somnolence ( 5 . 5 and 2 . 3 % ) . 