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: Antineutrophil cytoplasmic antibody ( ANCA ) - - associated vasculitis is a potentially life - threatening adverse effect of antithyroidmedications .
### Output Text:
Antineutrophil cytoplasmic antibody ( ANCA ) - - associated vasculitis is a potentially life - threatening adverse effect of <span class="chemical">antithyroidmedications</span> . 