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: Administration of the local anaesthetic bupivacaine ( 1 . 5 or 2 mg / kg , i . v . ) to rats elicited a marked decrease of mean arterial blood pressure ( MBP ) and heart rate ( HR ) leading to death ( in 67 % or 90 % of animals respectively ) .
### Output Text:
Administration of the local anaesthetic <span class="chemical">bupivacaine</span> ( 1 . 5 or 2 mg / kg , i . v . ) to rats elicited a marked decrease of mean arterial blood pressure ( MBP ) and heart rate ( HR ) leading to death ( in 67 % or 90 % of animals respectively ) . 