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: Telaprevir was considered the probable causative agent of an interaction with simvastatin according to the Drug Interaction Probability Scale .
### Output Text:
<span class="chemical">Telaprevir</span> was considered the probable causative agent of an interaction with <span class="chemical">simvastatin</span> according to the Drug Interaction Probability Scale . 