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: He received 500 ug of intravenous levothyroxine in the first 18 h of therapy , and 150 ug intravenous daily thereafter .
### Output Text:
He received 500 ug of intravenous <span class="chemical">levothyroxine</span> in the first 18 h of therapy , and 150 ug intravenous daily thereafter . 