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 single PPA / caffeine administration ( same dose ) lead to acute hypertension in both the normotensive and hypertensive animals .
### Output Text:
A single <span class="chemical">PPA</span> / <span class="chemical">caffeine</span> administration ( same dose ) lead to acute hypertension in both the normotensive and hypertensive animals . 