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: Nitroprusside infusion was associated with a significant ( p less than 0 . 05 ) increase in heart rate and cardiac output ; rebound hypertension was observed in three patients after discontinuation of nitroprusside .
### Output Text:
Nitroprusside infusion was associated with a significant ( p less than 0 . 05 ) increase in heart rate and cardiac output ; rebound hypertension was observed in three patients after discontinuation of <span class="chemical">nitroprusside</span> . 