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: These results suggest that PPA / caffeine can lead to cerebral hemorrhage in previously hypertensive animals when administered in greater than the allowed dosage .
### Output Text:
These results suggest that <span class="chemical">PPA</span> / <span class="chemical">caffeine</span> can lead to cerebral hemorrhage in previously hypertensive animals when administered in greater than the allowed dosage . 