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: In the third patient , the MPO - ANCA titre increased to 204 U / ml and she developed a higher fever , oral ulcers and polyarthralgia , but the symptoms resolved 2 weeks after stopping PTU therapy , and the MPO - ANCA titre decreased to 20 . 7 U / ml by 4 months after discontinuing PTU .
### Output Text:
In the third patient , the MPO - ANCA titre increased to 204 U / ml and she developed a higher fever , oral ulcers and polyarthralgia , but the symptoms resolved 2 weeks after stopping <span class="chemical">PTU</span> therapy , and the MPO - ANCA titre decreased to 20 . 7 U / ml by 4 months after discontinuing <span class="chemical">PTU</span> . 