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: Before admission , he had been taking nicergoline and bendazac lysine due to retinal vein occlusion at ophthalmologic department .
### Output Text:
Before admission , he had been taking <span class="chemical">nicergoline</span> and <span class="chemical">bendazac lysine</span> due to retinal vein occlusion at ophthalmologic department . 