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: This calls for attention when ketoconazole is administered to patients with risk factors for acquired long QT syndrome .
### Output Text:
This calls for attention when <span class="chemical">ketoconazole</span> is administered to patients with risk factors for acquired long QT syndrome . 