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: Unreported in the literature is visual hallucinations occurring in association with the new macrolide antibiotic , clarithromycin .
### Output Text:
Unreported in the literature is visual hallucinations occurring in association with the new <span class="chemical">macrolide</span> antibiotic , <span class="chemical">clarithromycin</span> . 