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 most common adverse events and median CD4 at time of event were rash ( 15 . 2 % ; CD4 , 285 cells / microL ) and peripheral neuropathy ( 9 . 0 % and 348 cells / microL ) .
### Output Text:
The most common adverse events and median CD4 at time of event were rash ( 15 . 2 % ; CD4 , 285 cells / microL ) and peripheral neuropathy ( 9 . 0 % and 348 cells / microL ) . 