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: Anesthesia was induced with 5 mg . kg ( - 1 ) thiopental iv . followed by succinylcholine ( Group PS , LS ) or rocuronium ( Group PR ) for tracheal intubation .
### Output Text:
Anesthesia was induced with 5 mg . kg ( - 1 ) <span class="chemical">thiopental</span> iv . followed by <span class="chemical">succinylcholine</span> ( Group PS , LS ) or <span class="chemical">rocuronium</span> ( Group PR ) for tracheal intubation . 