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: Alfentanil 50 micrograms kg - 1 effectively inhibits the incidence and intensity of suxamethonium - induced muscle fasciculations ; moreover , intragastric pressure remains at its control value .
### Output Text:
<span class="chemical">Alfentanil</span> 50 micrograms kg - 1 effectively inhibits the incidence and intensity of <span class="chemical">suxamethonium</span> - induced muscle fasciculations ; moreover , intragastric pressure remains at its control value . 