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 safety and efficacy of combination N - butyl - deoxynojirimycin ( SC - 48334 ) and zidovudine in patients with HIV - 1 infection and 200 - 500 CD4 cells / mm3 .
### Output Text:
The safety and efficacy of combination <span class="chemical">N - butyl - deoxynojirimycin</span> ( <span class="chemical">SC - 48334</span> ) and <span class="chemical">zidovudine</span> in patients with HIV - 1 infection and 200 - 500 CD4 cells / mm3 . 