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: Two cases of propylthiouracil - associated acute hepatitis , one case of fatal methimazole - associated hepatocellular necrosis and one case of propylthiouracil - associated lupus - like syndrome are described .
### Output Text:
Two cases of <span class="chemical">propylthiouracil</span> - associated acute hepatitis , one case of fatal <span class="chemical">methimazole</span> - associated hepatocellular necrosis and one case of <span class="chemical">propylthiouracil</span> - associated lupus - like syndrome are described . 