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: Steady - state pharmacokinetics of indinavir were done at week 4 after the initiation of indinavir .
### Output Text:
Steady - state pharmacokinetics of <span class="chemical">indinavir</span> were done at week 4 after the initiation of <span class="chemical">indinavir</span> . 