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: A 54 - year - old hypothyroid male taking thyroxine and simvastatin presented with bilateral leg compartment syndrome and myonecrosis .
### Output Text:
A 54 - year - old hypothyroid male taking <span class="chemical">thyroxine</span> and <span class="chemical">simvastatin</span> presented with bilateral leg compartment syndrome and myonecrosis . 