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: After discontinuing the oral alendronate , the patient underwent six cycles of hemodialysis and four cycles of LDL apheresis .
### Output Text:
After discontinuing the oral <span class="chemical">alendronate</span> , the patient underwent six cycles of hemodialysis and four cycles of LDL apheresis . 