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: Clinicians should be aware of potential hepatotoxicity with simvastatin - ezetimibe especially in elderly patients and should carefully monitor serum aminotransferase levels when starting therapy and titrating the dosage .
### Output Text:
Clinicians should be aware of potential hepatotoxicity with <span class="chemical">simvastatin - ezetimibe</span> especially in elderly patients and should carefully monitor serum aminotransferase levels when starting therapy and titrating the dosage . 