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: Abstract Serum aminotransferase elevations are a commonly known adverse effect of 3 - hydroxy - 3 - methylglutaryl coenzyme A reductase inhibitor ( statin ) therapy .
### Output Text:
Abstract Serum aminotransferase elevations are a commonly known adverse effect of 3 - hydroxy - 3 - methylglutaryl coenzyme A reductase inhibitor ( <span class="chemical">statin</span> ) therapy . 