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: CASE SUMMARY : A 76 - year - old man presented with persistent hiccups after beginning azithromycin for the treatment of pharyngitis .
### Output Text:
CASE SUMMARY : A 76 - year - old man presented with persistent hiccups after beginning <span class="chemical">azithromycin</span> for the treatment of pharyngitis . 