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: Studies in DBA / 2J mice showed that : 1 ) pretreatment with acetaminophen ( 100 mg / kg ) increased the interval between the administration of caffeine ( 300 to 450 mg / kg IP ) and the onset of fatal convulsions by a factor of about two ; and 2 ) pretreatment with acetaminophen ( 75 mg / kg ) reduced the incidence of audiogenic seizures produced in the presence of caffeine ( 12 . 5 to 75 mg / kg IP ) .
### Output Text:
Studies in DBA / 2J mice showed that : 1 ) pretreatment with <span class="chemical">acetaminophen</span> ( 100 mg / kg ) increased the interval between the administration of <span class="chemical">caffeine</span> ( 300 to 450 mg / kg IP ) and the onset of fatal convulsions by a factor of about two ; and 2 ) pretreatment with <span class="chemical">acetaminophen</span> ( 75 mg / kg ) reduced the incidence of audiogenic seizures produced in the presence of <span class="chemical">caffeine</span> ( 12 . 5 to 75 mg / kg IP ) . 