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: Cardiotoxicity has been demonstrated after both intravenous and oral administration of erythromycin but has never been reported with the newer macrolides .
### Output Text:
Cardiotoxicity has been demonstrated after both intravenous and oral administration of <span class="chemical">erythromycin</span> but has never been reported with the newer <span class="chemical">macrolides</span> . 