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: However , these animals had shown a significant increase in heart rate beginning at 8 weeks after drug administration ( P less than 0 . 01 ) . ( ABSTRACT TRUNCATED AT 400 WORDS )
### Output Text:
However , these animals had shown a significant increase in heart rate beginning at 8 weeks after drug administration ( P less than 0 . 01 ) . ( ABSTRACT TRUNCATED AT 400 WORDS ) 