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: The patient was maintained on levothyroxine 175 ( g POorally daily .
### Output Text:
The patient was maintained on <span class="chemical">levothyroxine</span> 175 ( g POorally daily . 