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: This randomized double - blind crossover outpatient study assessed the preference for 1 rizatriptan 10 mg tablet to 2 ergotamine 1 mg / caffeine 100 mg tablets in 439 patients treating a single migraine attack with each therapy .
### Output Text:
This randomized double - blind crossover outpatient study assessed the preference for 1 <span class="chemical">rizatriptan</span> 10 mg tablet to 2 <span class="chemical">ergotamine</span> 1 mg / <span class="chemical">caffeine</span> 100 mg tablets in 439 patients treating a single migraine attack with each therapy . 