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: Formation of coronary aneurysm is a rare complication of stenting with bare metal stents , but based on experimental studies drug - eluting stents may induce toxic effects on the vessel wall with incomplete stent apposition , aneurysm formation and with the potential of stent thrombosis or vessel rupture .
### Output Text:
Formation of coronary aneurysm is a rare complication of stenting with bare metal stents , but based on experimental studies drug - eluting stents may induce toxic effects on the vessel wall with incomplete stent apposition , aneurysm formation and with the potential of stent thrombosis or vessel rupture . 