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: OBJECTIVE : To review the natural history and ocular and systemic adverse effects of patients taking hydroxychloroquine sulfate who attended an ophthalmic screening program .
### Output Text:
OBJECTIVE : To review the natural history and ocular and systemic adverse effects of patients taking <span class="chemical">hydroxychloroquine sulfate</span> who attended an ophthalmic screening program . 