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: The infusion was discontinued either when there was no muscular response to tetanic stimulation of the ulnar nerve or when Sch 120 mg was exceeded .
### Output Text:
The infusion was discontinued either when there was no muscular response to tetanic stimulation of the ulnar nerve or when <span class="chemical">Sch</span> 120 mg was exceeded . 