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 mean SC - 48334 steady - state trough level ( 4 . 04 + / - 0 . 99 micrograms / ml ) was below the in vitro inhibitory concentration for human immunodeficiency virus ( HIV ) .
### Output Text:
The mean <span class="chemical">SC - 48334</span> steady - state trough level ( 4 . 04 + / - 0 . 99 micrograms / ml ) was below the in vitro inhibitory concentration for human immunodeficiency virus ( HIV ) . 