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 : Myeloperoxidase antineutrophil cytoplasmic antibody ( MPO - ANCA ) - positive vasculitis has been reported in patients with Graves ' disease who were treated with propylthiouracil ( PTU ) .
### Output Text:
OBJECTIVE : Myeloperoxidase antineutrophil cytoplasmic antibody ( MPO - ANCA ) - positive vasculitis has been reported in patients with Graves ' disease who were treated with <span class="chemical">propylthiouracil</span> ( <span class="chemical">PTU</span> ) . 