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: Reports of persistent paralysis after the discontinuance of these drugs have most often involved aminosteroid - based NMBAs such as vecuronium bromide , especially when used in conjunction with corticosteroids .
### Output Text:
Reports of persistent paralysis after the discontinuance of these drugs have most often involved aminosteroid - based NMBAs such as <span class="chemical">vecuronium bromide</span> , especially when used in conjunction with corticosteroids . 