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: We describe a 47 - year - old woman with an acute myocardial infarction after administration of sumatriptan 6 mg subcutaneously for cluster headache .
### Output Text:
We describe a 47 - year - old woman with an acute myocardial infarction after administration of <span class="chemical">sumatriptan</span> 6 mg subcutaneously for cluster headache . 