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: Daptomycin serum and CSF trough concentrations were 11 . 21 ug / mL and 0 . 52 ug / mL , respectively , prior to the third dose .
### Output Text:
<span class="chemical">Daptomycin</span> serum and CSF trough concentrations were 11 . 21 ug / mL and 0 . 52 ug / mL , respectively , prior to the third dose . 