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: BACKGROUND : Prolonged administration of indinavir is associated with the occurrence of a variety of renal complications in adults .
### Output Text:
BACKGROUND : Prolonged administration of <span class="chemical">indinavir</span> is associated with the occurrence of a variety of renal complications in adults . 