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: Although the side - effect profile of erythromycin is established , including gastroenteritis and interactions with other drugs subject to hepatic mixed - function oxidase metabolism , experience with the newer macrolides is still being recorded .
### Output Text:
Although the side - effect profile of <span class="chemical">erythromycin</span> is established , including gastroenteritis and interactions with other drugs subject to hepatic mixed - function oxidase metabolism , experience with the newer <span class="chemical">macrolides</span> is still being recorded . 