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: Indinavir - associated nephrotoxicity must be monitored closely , especially in children with risk factors such as persistent sterile leukocyturia , age < 5 . 6 years , an area under the curve of indinavir > 19 mg / L x h , and a C ( max ) > 12 mg / L .
### Output Text:
<span class="chemical">Indinavir</span> - associated nephrotoxicity must be monitored closely , especially in children with risk factors such as persistent sterile leukocyturia , age < 5 . 6 years , an area under the curve of <span class="chemical">indinavir</span> > 19 mg / L x h , and a C ( max ) > 12 mg / L . 