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: Sulindac was substituted for naproxen and no further adverse renal effects occurred over the next 12 months .
### Output Text:
<span class="chemical">Sulindac</span> was substituted for <span class="chemical">naproxen</span> and no further adverse renal effects occurred over the next 12 months . 