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: A patient who allegedly consumed 100 tablets of an over - the - counter analgesic containing sodium acetylsalicylate , caffeine , and acetaminophen displayed no significant CNS stimulation despite the presence of 175 micrograms of caffeine per mL of serum .
### Output Text:
A patient who allegedly consumed 100 tablets of an over - the - counter analgesic containing <span class="chemical">sodium acetylsalicylate</span> , <span class="chemical">caffeine</span> , and <span class="chemical">acetaminophen</span> displayed no significant CNS stimulation despite the presence of 175 micrograms of <span class="chemical">caffeine</span> per mL of serum . 